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Greenhouse and field evaluation of fungicides for control of olive leaf spot in New Zealand
ARTICLE IN PRESS Crop Protection 27 (2008) 1335– 1342
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Greenhouse and field evaluation of fungicides for control of olive leaf spot in New Zealand Friday O. Obanor a,, Marlene V. Jaspers a, E. Eirian Jones a, Monika Walter b a b
Bio-Protection and Ecology Division, Lincoln University, P.O. Box 84, Canterbury, New Zealand HortResearch, P.O. Box 51, Lincoln, Canterbury, New Zealand
a r t i c l e in fo
abstract
Article history: Received 10 December 2007 Received in revised form 29 April 2008 Accepted 29 April 2008
Olive leaf spot, a major disease of olive worldwide, is difficult to control in regions with cool and moist weather conditions such as New Zealand. The fungicides, boscalid, captan, carbendazim, copper hydroxide, copper sulphate, difenoconazole, dodine, kresoxim-methyl and a kresoxim-methyl/copper hydroxide mixture, were tested for efficacy in greenhouse and field trials. Greenhouse studies showed that all fungicides significantly reduced disease severity but the level of control was affected by the time interval between fungicide application and pathogen inoculation. For the field study, trees in commercial olive groves in three regions received two fungicide applications in each of three consecutive seasons: winter, spring and autumn. Fungicide type and time of application affected the disease incidence on the leaves. In winter, none of the fungicides, except copper sulphate and copper hydroxide, reduced disease incidence on the leaves compared with unsprayed controls. Most of the fungicides reduced disease incidence after spring and autumn applications, with the autumn applications being the most effective. Of the fungicides tested, copper sulphate and a mixture of kresoxim-methyl and copper hydroxide were the most effective, reducing disease incidence by 85–96% and 63–93%, respectively. Fungicide efficacy was greater in the drier climatic regions of New Zealand than the wetter regions. The results of this research facilitated the development of an improved fungicide spray programme for control of olive leaf spot in New Zealand. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Olives Spilocaea oleagina Peacock spot Cycloconium leaf spot Fungicides
1. Introduction Olive leaf spot (OLS), also known as peacock spot or Cycloconium leaf spot, is caused by the fungus Spilocaea oleagina (Castagne) Hughes. The disease causes severe premature defoliation of olive (Olea europaea L.), and sometimes leads to twig death (Miller, 1949; Azeri, 1993). Infection of fruit can cause unacceptable blemishes on table olives, and when it occurs on oilproducing cultivars, infection may cause a delay in ripening and a decrease in oil yields (Verona and Gambogi, 1964). The disease is common worldwide and serious in cooler olive-growing regions, with yield losses estimated to be as high as 20% (Wilson and Miller, 1949). In New Zealand, S. oleagina infection occurs during autumn through to early spring and the pathogen is dormant during hot, dry summers (Obanor et al., 2005a). S. oleagina survives during summer as mycelium in the lesions on living leaves. In autumn, the margins of these lesions expand into adjacent healthy tissues
Corresponding author. Current address: CSIRO Plant Industry, 306 Carmody Road, St. Lucia, QLD 4067, Australia. Tel.: +617 32142913; fax: +617 32142920. E-mail address: [email protected] (F.O. Obanor).
0261-2194/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2008.04.007
from where conidia are produced and then dispersed by rain splash and run-off (Miller, 1949). Moist weather conditions favour S. oleagina sporulation, conidium germination and infection, and young olive leaves are more susceptible to infection than older ones (Graniti, 1993). Obanor et al. (2008) reported that conidium production was optimal at 15 1C and under high humidity (100%), whereas conidium germination and infection required continuous free moisture for 12–24 h and temperatures ranging from 5 to 25 1C. These conditions are common in New Zealand olive groves, particularly in autumn and early spring when new leaves are formed. Application of copper-based fungicides is the main method of OLS control throughout olive-growing regions of the world (Teviotdale et al., 1989; Graniti, 1993). Timing of the fungicide applications is vital for effective control of OLS (Graniti, 1993). In the Mediterranean region, fungicides are usually applied before the onset of the main infection periods, which often coincide with the main shoot-growth seasons (spring and/or autumn) (Prota, 1995). In Californian olive groves, Teviotdale et al. (1989) reported that one annual application of copper-containing fungicides in late autumn, before the rainy period, effectively controlled OLS under low disease pressure. However, in New Zealand olive groves, multiple applications of copper-containing and/or
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systemic fungicides are commonly used annually, but often fail to provide effective control, resulting in very high disease levels in some regions (MacDonald et al., 2000). Apple scab, caused by Venturia inaequalis, has been successfully controlled by systemic fungicides such as carbendazim, difenoconazole and fenarimol (Dahmen and Staub, 1992). Given that S. oleagina and V. inaequalis are closely related and have similar modes of infection (Graniti 1993), it is likely that fungicides which control V. inaequalis could be effective in controlling OLS. An in vitro evaluation using fungicides known to be effective against V. inaequalis showed that the systemic fungicides, carbendazim and kresoxim-methyl, have the potential to effectively inhibit conidium germination and germ tube growth of S. oleagina (Obanor et al., 2005b). These fungicides are more target-specific than contact fungicides such as captan and copper-containing fungicides, and may also have a curative effect when applied within 10 d of infection (Viruega and Trapero, 2002). In Israel, Shabi et al. (1994) reported that 89–95% of the leaves on olive trees treated in autumn with a mixture of difenoconazole (Score 25 EC) and mineral oil (Texaco Spraytex CT774) were free from OLS when assessed the following spring, whereas only 66–82% of the leaves from trees treated with copper sulphate (Bordeaux Mixture) were free from the disease. This research investigated the rate, number and timing of different fungicides for their effectiveness in controlling OLS under field conditions in New Zealand.
dazim) (MacDonald et al., 2000). To evaluate the protective and/or curative activity of the fungicides, they were applied to the whole plants 0, 1, 3 or 7 d before or 1, 3 or 7 d after S. oleagina inoculation. Fungicides were applied with a hand-held spray bottle until runoff, using a volume of 10–15 ml per plant. For the day-0 treatment, sprayed plants were allowed to dry for 2 h prior to inoculation. On the day of inoculation (day 0), a suspension of 5.0 104 S. oleagina conidia ml1 was made by washing conidia from naturally infected olive leaves (cv. Barnea) as described by Saad and Masri (1978). The suspension was sprayed onto plants using an atomizer to just before run-off. For the next 7 d, the plants were enclosed within a clear polythene tent constructed inside the greenhouse to increase relative humidity and provide sufficient moisture for infection. For the fungicide applications 1 and 3 d post inoculation, the plants were treated and returned to the tent. However, the 7-d post-inoculation treatment was applied 30 min before all plants were transferred to the shadehouse for disease symptoms to develop. The mean daily temperature in the shadehouse ranged from 10 to 15 1C and moisture was supplied by an overhead misting system that operated for 10 min per day. There were four replicate plants for each treatment combination (products and application times), a total of 280 plants, which were arranged in a completely randomized design. After 12 weeks, the mean number of lesions per leaf was assessed for the six leaves marked at the time of inoculation. Lesion number per leaf had previously been shown to be a good estimate of disease severity (Obanor et al., 2005a). The experiment was conducted twice.
2. Materials and methods 2.1. Greenhouse experiments
2.2. Field trials
The experiment was conducted on 1–2-year-old olive plants of the cultivar ‘Barnea’, which is highly susceptible to OLS (Graniti, 1993). The plants were grown individually in 1 l plastic pots containing a mixture of composted bark and pumice (4:1, v/v) with slow release fertilizer (N:P:K ¼ 15:4:7.5) in a greenhouse maintained at 2275 1C and 30–60% RH. The youngest six fully expanded leaves were marked at the beginning of the trial. The fungicides used for the trial (Table 1) were those that had demonstrated high efficacy in controlling OLS in the in vitro assays (kresoxim-methyl, boscalid and captan) (Obanor et al., 2005b) and those commonly used for OLS control in New Zealand (copper sulphate, difenoconazole, copper hydroxide, dodine and carben-
Field trials were conducted in commercial olive groves in three regions: Canterbury (C), Blenheim (B) and Auckland (A). Two groves (I and II) from each region were selected, each of which had a history of OLS and had trees that were 6–8 years old and spaced on a 6 6 m grid. The Canterbury and Blenheim groves contained ‘Barnea’ trees, whereas in Auckland, the groves contained cultivar ‘Picual’. Methods of fertilizer application, irrigation and other cultural practices were similar for all groves and followed the standard procedures described in the New Zealand manual for commercial olive growers’ (Olive New Zealand, 2004). Temperature and rainfall data were collected for each region throughout the duration of the trials.
Table 1 Fungicide treatments used for the greenhouse (G) trial in Canterbury and the field trials (F) in Auckland (A), Blenheim (B) and Canterbury (C) Experiment Region Treatment
Product name and formulation
A.i. conc.a (g kg1)
Product rate (l1 water)
Supplier
G G, F G, F G G, F F F
Water B Boscalid A, B, C Captan Carbendazim C Copper hydroxide C Copper hydroxide C Copper hydroxide
– Endura 50 WG Crop Care Captan WG Bavistins DF ChampTM DP (rate 1) ChampTM DP (rate 2) Kocide 2000 DF
– 700 800 500 375 375 350
– 0.1 g 1.25 g 0.16 g 1.75 g 2.5 g 1.9 g
G, F G, F
A, B, C Copper sulphate A, B, C Difenoconazole
Cuprofixs Disperss Scores 10 WG
200 100
5g 0.25 g
G G, F G, F
Dodine A, B, C Kresoxim-methyl B, C Kresoxim-methyl/copper hydroxide (KK mixture)
Dodine 400 Strobys WG Strobys WG/ Kocide 2000 DF
400 500 500 350
0.18 ml 0.1 g 0.05 g 0.95 g
– BASF NZ Ltd. Nufarm Ltd. BASF NZ Ltd. Nufarm Ltd. Nufarm Ltd. Du Pont and Elliott Chemicals Nufarm Ltd. Syngenta Crop Protection Ltd. Nufarm Ltd. BASF NZ Ltd. BASF NZ Ltd. Du Pont and Elliott Chemicals
a
A.i. ¼ active ingredient concentration.
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Each fungicide treatment was applied to four-tree plots, all plots arranged in a completely randomized block design, replicated in five blocks for all groves. Each plot was separated from the next one in the row by one to five buffer trees (depending on the grove and layout) and from the plots in adjacent rows by one buffer row. Controls comprised plots of unsprayed trees. Each fungicide was applied twice in winter 2004, spring 2004 and autumn 2005 (Table 2), using growers’ spray equipment comprising hydraulic boom sprayer fitted with hollow-cone nozzles. Treatments were applied with water volumes of 1000–1200 l ha1, depending on the size of the trees. No other fungicides were sprayed on the trial trees, but all other normal grower practices were performed throughout the duration of the trials. In all groves, the fungicides, captan, kresoxim-methyl, difenoconazole or copper sulphate, were tested at the rates specified in Table 1. However in Canterbury and Blenheim, copper hydroxide, a kresoxim-methyl and copper hydroxide mixture (KK mixture) and boscalid were also included in the trial (Table 1). The effect of fungicide application in autumn was determined by applying a selected treatment to a subset of trees within the experimental plots. The autumn 2005 applications occurred in the same groves and trial plots used for winter and spring 2004 except that each four-tree trial plot was halved, resulting in a split-plot design, with half of the trees (randomly selected) receiving only two applications in winter and spring and the other half receiving two additional applications in autumn. The efficacy of a KK mixture was tested only in spring 2004 and autumn 2005 in Canterbury (Grove I) and in autumn 2005 in both Table 2 Sites, cultivars, application and assessment dates for field trials in 2004–2005 Region
Grove
Cultivar
Season
Application dates
Canterbury
I
Barnea
Winter
09 Jul. 2004 21 Jul. 2004 04 Nov. 2004 18 Nov. 2004 05 Apr. 2005 19 Apr. 2005 11 Jul. 2004 21 Jul. 2004 07 Nov. 2004 17 Nov. 2004 10 Apr. 2005 20 Apr. 2005
Spring Autumn II
Barnea
Winter Spring Autumn
Blenheim
I
Barnea
Winter Spring Autumn
II
Barnea
Winter Spring Autumn
Auckland
I
Picual
Winter Spring Autumn
II
Picual
Winter Spring Autumn
a
20 Jul. 2004 03 Aug. 2004 02 Nov. 2004 12 Nov. 2004 29 Apr. 2005 13 May. 2005 20 Jul. 2004 03 Aug. 2004 02 Nov. 2004 12 Nov. 2004 29 Apr. 2005 13 May 2005 31 Jul. 2004 13 Aug. 2004 01 Nov. 2004 10 Nov. 2004 03 Apr. 2005 12 Apr. 2005 01 Aug. 2004 14 Aug. 2004 17 Oct. 2004 27 Oct. 2004 30 Apr. 2005 14 May 2005
1337
groves in Blenheim. In Canterbury, KK mixture was applied to four-tree plot replicated in five blocks in spring 2004 but in autumn 2005, the fungicide was applied to two randomly selected trees from each control plot at both sites. Disease was evaluated at the beginning of the trial (June 2004), 2–3 months later in spring and then 4–5 months after the autumn treatments as shown in Table 2. On each occasion, one branch per tree was randomly selected on the south side at eye level. On this branch, 100 fully expanded matured leaves were removed and evaluated for disease incidence, which was expressed as the percentage of infected leaves.
2.3. Statistical analysis All data were subjected to analysis of variance (ANOVA) to evaluate the effect of treatment, time of application and their interaction. For the greenhouse data, there was homogeneity of error variances and so the data for the two experimental repeats were combined. However, due to heterogeneity of error variances in the field trials, data for each region and grove were analysed separately. Disease incidence was transformed to relative disease incidence compared with the untreated control, which was assigned a value of 100. Treatment means were compared using Fisher’s unprotected least significant difference test at the 5% probability level. Histograms, normal probability and scatter plots of the residuals were examined and there was no evidence of violation of the assumptions underlying the models used for ANOVA. All statistical analyses were conducted using Genstat 9.0 (Lawes Agricultural Trust, Rothamsted Experimental Station, Harpenden, UK).
Assessment dates
3. Results 12 Oct. 2004
3.1. Greenhouse experiments 20 Apr. 2005 10 Sept.2005 11 Oct.2004 20 Apr. 2005 10 Sept. 2005
19 Oct. 2004 16 Apr. 2005 02 Sept. 2005 19 Oct. 2004 16 Apr. 2005 –a
10 Oct. 2004 31 Mar. 2005 15 Sept. 2005
The main effects of treatment, time and the treatment time interaction were highly significant (Po0.001), and the means of experimental repeats did not differ significantly (P ¼ 0.326). At 12 weeks after inoculation, all plants that had received fungicides had significantly fewer leaf lesions than untreated control plants, for all application times except for dodine applied 7 d before pathogen inoculation (Table 3). When fungicides were applied before pathogen inoculation, the pre-inoculation interval did not affect numbers of leaf lesions per plant for most fungicides except for carbendazim, difenoconazole and kresoxim-methyl whose efficacy varied across the interval, and was generally greater if applied near the inoculation time. When fungicides were applied after inoculation, there was a reduction in efficacy after 3 d for captan, difenoconazole, copper hydroxide and copper sulphate and after 7 d for all other fungicides. The most effective fungicides were copper sulphate, kresoxim-methyl and KK mixture, all of which reduced disease severity by 74–99% when applied up to 7 d before inoculation and 1 d after inoculation (Table 3). The least effective fungicide was dodine, which reduced disease severity in the range 13–57% over the same period.
3.2. Field trials
10 Oct. 2004 31 Mar. 2005 15 Sept. 2005
Data were not collected from the trees because they had been removed.
Temperature and rainfall data collected for each region during the period of the trial, April 2004 through September 2005, are shown in Fig. 1. The average daily temperature in Auckland, Blenheim and Canterbury ranged from 6 to 23 1C, 3 to 24 1C and 2 to 23 1C, respectively. The total amount of rainfall recorded in
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Table 3 Olive leaf spot severity 12 weeks after inoculation with S. oleagina conidia and treatment at various times relative to the inoculation event Fungicidea
Control Boscalid Captan Carbendazim Copper hydroxided Copper sulphate Difenoconazole Dodine Kresoxim-methyl KK mixture LSDc (Po0.05)
Disease severityb
LSDc
Days before inoculation
Days after inoculation
7
3
1
0
1
3
7
82 32 36 63 19 5 55 71 21 5 14.2
82 19 29 45 22 3 49 65 16 2 12.1
88 25 24 51 25 5 34 61 5 3 10.7
89 18 26 19 20 2 29 57 10 1 9.9
96 14 23 21 27 6 22 41 8 4 11.3
86 23 36 34 56 59 38 44 13 3 13.8
94 50 59 67 62 70 74 71 24 6 16.1
(Po0.05)
20.9 13.3 10.5 15.6 14.9 8.0 12.9 13.7 7.5 3.2
the mean disease incidence being reduced by 64–96%. Overall, the most consistent and effective fungicides were the KK mixture and copper sulphate. By the end of the trials, these two treatments had reduced disease incidence by 85–96% and 63–93%, respectively, in all the groves except in Auckland (Grove II) in which copper sulphate failed to control the disease. The effects of additional fungicide applications in autumn are shown in Fig. 3. For those fungicides that were shown to be effective in spring in all groves, two additional sprays in the following autumn significantly (Po0.001) reduced disease incidence (Fig. 3). In Canterbury Grove I, for example, disease incidence was approximately 25% on trees that received six applications of copper sulphate over three seasons, compared with about 65% incidence for those that received four applications across winter and spring 2004 (Fig. 3). In addition, two applications of kresoxim in autumn only significantly (Po0.001) reduced disease incidence compared with the control in both Canterbury Grove I and Blenheim Grove I.
a
Fungicide application rates are shown in Table 1. Mean number of leaf lesions per plant (six leaves per plant and four plants per treatment) averaged over the two experimental repeats. c Least significant difference. d Fisher’s unprotected least significant difference (LSD). b
Canterbury and Blenheim was 811 and 1320 mm, respectively, whereas in Auckland a total of 1580 mm was recorded. Disease progression on unsprayed trees in Auckland, Canterbury and Blenheim olive groves during 2004 and 2005 is shown in Fig. 2. At all sites, with the exception of Grove II in Auckland, there was a progressive increase in disease incidence in untreated plots throughout the season, with the most rapid increase occurring over the winter months (April and September). In several groves, OLS incidence reached 100% and total defoliation occurred soon after, with 100% fruit infection and zero yields observed in the Canterbury and Auckland regions. The incidence of OLS in the experimental groves sprayed with different fungicides at different times is shown in Table 4. The main effects of treatment, time and the treatment time interaction were highly significant (Po0.001) under field conditions, but differed between groves and regions. The relative performance of individual fungicides also differed according to the timing of application as indicated by the significant treatment and application time interaction. In winter 2004, two applications of each fungicide generally resulted in a small and non-significant reduction in disease incidence when compared with the unsprayed control in all the groves. The exceptions were copper as copper sulphate (Cuprofixs disperss) and copper hydroxide (ChampTM DP: 2.5 g l1) applied in Canterbury, and kresoxim-methyl in Blenheim (Grove II), where there was a small but significant (Po0.05) reduction in disease incidence. There was high disease incidence on all trees, resulting in severe defoliation of the trees in all groves irrespective of the treatment. In addition, leaf tissue damage was observed on trees treated with copper-containing fungicides in all groves, particularly in Canterbury groves, indicating copper phytotoxicity. The efficacy of the various fungicides (Table 4) varied according to the regions, being most effective overall in Blenheim, where the disease pressure was lowest. In spring 2004 and autumn 2005, a tank mix of kresoxim-methyl (Strobys WG) and copper hydroxide (Kocide 2000 DF), which were used in only one Canterbury grove and one Blenheim grove provided the best OLS control, although this treatment was not statistically different from copper sulphate. At all other groves, copper sulphate was the most effective single fungicide. For the autumn 2005 applications, all the fungicides were highly effective in Blenheim Grove I, with
4. Discussion In the greenhouse trial, fungicides representing seven chemical classes reduced OLS severity on olive foliage when applied from 7 d before to 3 d after inoculation. Copper sulphate, kresoximmethyl and KK mixture were the most effective in protecting young olive leaves from OLS infection. In a previous study, Obanor et al. (2005b) reported that kresoxim-methyl and captan were effective in inhibiting conidium germination but the two coppercontaining fungicides, copper hydroxide and copper sulphate, were ineffective, which suggests that copper sulphate may act through means other than by inhibition of germination. Generally, all the fungicides provided protective and curative activity against OLS for up to 3 d after inoculation, possibly because of the slow growth of the pathogen (Obanor et al., 2008). The curative effect of kresoxim-methyl alone or in a copper mixture persisted 7 d after inoculation. This result was consistent with that of Viruega and Trapero (2002) who showed that mixing kresoxim-methyl with cupric or organocupric fungicides significantly reduced OLS severity up to 10 d after inoculation. A similar result was also reported for the closely related pathogen V. inaequalis (Ypema and Gold, 1999), eccept for dodine which showed high curative activity against the apple scab fungus, V. inaequalis when applied 48 or 144 h after inoculation (Gupta and Kumar, 1985; Thakur et al., 1992), but was relatively ineffective against OLS. The curative activity of a fungicide is related to its mode of action, the efficacy of its absorption and distribution within the leaf, and the position and mass of the invading pathogen. The low efficacy of difenoconazole, dodine and carbendazim, which are known to have curative, systemic activity against V. inaequalis (Ypema and Gold, 1999) might have been due to inadequate levels of active ingredients being absorbed by olive leaves. In vivo screening is considered to be a robust and relevant strategy for determining fungicide performance in the field, particularly with systemic fungicides (Knight et al., 1997). In this study, the efficacy of most fungicides was less in the field than in the greenhouse but ranking of fungicide effectiveness was similar. Overall, the copper-containing fungicides (some with kresoximmethyl) were the most effective, which supports the common usage of copper-containing fungicides, including copper sulphate, copper oxychloride, copper hydroxide and copper oxide in olivegrowing regions, such as California, Greece and Italy (Wilson and Miller, 1949; Bourbos and Skoudridakis, 1993; Teviotdale and Sibbett, 1995; Iannotta et al., 2002). Difenoconazole has been shown to have both protective and curative activity against
ARTICLE IN PRESS F.O. Obanor et al. / Crop Protection 27 (2008) 1335–1342
25 Auckland
1339
Rain Temperature
80 70
20
50
15
40 10
Rain (mm)
Temperature (°C)
60
30 20
5 10 0 0 1-May-04 1-Jul-04 1-Sep-04 1-Nov-04 1-Jan-05 1-Mar-05 1-May-05 1-Jul-05 1-Sep-05 25 Blenheim
Rain Temperature
80 70
20
50
15
40 10
Rain (mm)
Temperature (°C)
60
30 20
5 10 0 0 1-May-04 1-Jul-04 1-Sep-04 1-Nov-04 1-Jan-05 1-Mar-05 1-May-05 1-Jul-05 1-Sep-05 25 Canterbury
Rain Temperature
80 70
20
15
50 40
10
Rain (mm)
Temperature (°C)
60
30 20
5 10 0 0 1-May-04 1-Jul-04 1-Sep-04 1-Nov-04 1-Jan-05 1-Mar-05 1-May-05 1-Jul-05 1-Sep-05 Fig. 1. Daily rainfall and average daily temperature in Auckland, Blenheim and Canterbury from 1 May 2004 to 30 September 2005.
V. inaequalis (Dahmen and Staub, 1992), but the efficacy of this fungicide in controlling OLS was not consistent, except in Blenheim groves where there was low disease pressure. In Israel, however, Shabi et al. (1994) reported that difenoconazole was
more effective than copper-containing fungicides, particularly when it was mixed with petroleum oil. They found that when olive trees were treated in autumn with difenoconazole (Score 25 EC) mixed with oil, 89–95% of the leaves were free from OLS when
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Auckland I Auckland II Canterbury I Canterbury II Blenheim I Blenheim II
Disease incidence (%)
100 80 60 40 20 0
Jun. 2004
Oct. 2004 Apr. 2005 Assessment date
Sept. 2005
Fig. 2. Mean olive leaf spot incidence in unsprayed trees in two commercial olive groves (I and II) in Canterbury, Blenheim and Auckland between 2004 and 2005. No data were collected for Blenheim Grove II in spring 2005 because the trees had been removed. Bars represent the standard errors of the means.
assessed 4–5 months later, whereas with copper sulphate, 66–82% of the leaves from treated trees were free of the disease. With another demethylation inhibitor fungicide, tebuconazole, Iannotta et al. (2002) reported that in Italy two applications in spring did not reduce S. oleagina infections compared with the controls. The inconsistencies in the reports may be attributed to differences in the environmental conditions, disease levels and timing of applications as this study indicated that autumn applications had the greatest overall effect on medium-term disease control. In this study, OLS incidence on untreated trees in commercial olive groves increased at a faster rate during the period April–September 2005 when compared with the winter period in the previous year, especially in Auckland and Canterbury. The weather conditions during these two periods were similar and unlikely to account for the differences in OLS incidence. The most probable reason for the rapid increase in disease levels in 2005 was inoculum build-up on trees which received no fungicides over the 15 months period of the trial. Efficacy of the fungicides tested in this study was greater in Canterbury and Blenheim than in Auckland. The poor performance of the fungicides in Auckland olive groves may be attributed to the environmental conditions being more favourable for OLS development (Graniti, 1993). In addition, the higher
Table 4 Olive leaf spot incidence on olive trees in commercial groves, which were sprayed with different fungicides and at different times in 2004 and 2005, relative to the unsprayed control treatment. Actual disease incidence values for the unsprayed controls are shown in parentheses Relative disease incidence2 (%) Canterbury
Blenheim
Auckland
Application time1
Fungicide
I
II
I
II
I
II
Jul. 2004 (Winter)
Control Copper sulphate Captan Difenoconazole Kresoxim-methyl Boscalid Copper hydroxide (Kocide 2000 DF) Copper hydroxide (ChampTM DP rate 1) Copper hydroxide (ChampTM DP rate 2) KK mixture
100a (25) 80b 95ab 88ab 90ab – 87ab 86ab 82b –
100a (39) 81b 90ab 96ab 88ab – – – – –
100a (12) 87a 91a 96a 87a 89a – – – –
100a (19) 84ab 82ab 81ab 78b 83ab – – – –
100a (25) 94a 92a 91a 94a – – – – –
100a (40) 82a 91a 90a 92a – – – – –
Nov. 2004 (Spring)
Control Copper sulphate Captan Difenoconazole Kresoxim-methyl Boscalid Copper hydroxide (Kocide 2000 DF) Copper hydroxide (ChampTM DP rate 1) Copper hydroxide (ChampTM DP rate 2) KK mixture
100a (39) 26ef 83bc 91ab 80bc – 73c 55d 33e 11f
100a (50) 33c 62b 80b 72b – – – – –
100a (18) 41c 74b 65b 56bc 60b – – – –
100a (32) 53c 65bc 70bc 73bc 83ab – – – –
100a (51) 81b 100a 86ab 100a – – – – –
100a (52) 100a 82a 84a 91a – – – – –
Apr. 2005 (Autumn)
Control Copper sulphate Captan Difenoconazole Kresoxim-methyl Boscalid Copper hydroxide (Kocide 2000 DF) Copper hydroxide (ChampTM DP rate 1) Copper hydroxide (ChampTM DP rate 2) KK mixture4
100a (100) 28ef 83bc 89ab 80bc – 49d 42de 23f 15f
100a (100) 25d 84ab 64c 67bc – – – – –
100a (48) 7cd 19c 14c 14c 36b – – – 4d
–3
100a (100) 37c 100a 94ab 76b – – – – –
100a (100) 100a 71b 89ab 69b – – – – –
1
– – – – – – – –
Treatments were applied twice in winter, spring and autumn using the same groves and trees. Application and assessment dates are shown in Table 2. Mean numbers of infected leaves per tree (100 leaves per tree and four trees per treatment plot). Means in a column within the same season followed by different letters are significantly different at P ¼ 0.05. 3 No data were collected for Blenheim Grove II because the trees were removed. 4 Treatment was applied to two randomly selected trees from each control plot. 2
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Disease incidence (%)
100
Oct. 2004 Apr. 2005 Assessment date
Sept. 2005
incidence of up to 100% can be found in New Zealand groves, where the environmental conditions (cool and wet) favour OLS development. Treatment history may also have cumulative effects on OLS severity in any given season. Spraying olives in one season might influence the amount of disease development the following season, either by causing a reduction in the inoculum levels in the trees or through the effect of fungicide residues which remain on the leaves until the next season. In this study, when the most effective fungicide, copper sulphate, was applied to trees in spring 2004 but not in autumn 2005, the fungicide was less effective on OLS when assessed in winter 2005 than the trees that also received the autumn applications. This is consistent with reports of Wilson and Miller (1949) and Teviotdale and Sibbett (1995), which showed that in Californian groves, OLS severity gradually decreased in trees treated annually. In addition, trees treated in 1 year had less OLS than non-treated trees in the subsequent year when all the trees were left untreated (Teviotdale and Sibbett, 1995). This study has shown that OLS in New Zealand groves can be controlled effectively by two applications of either copper sulphate (Cuprofixs Disperss) or a mixture of kresoxim-methyl (Strobys WG) and copper hydroxide (Kocide 2000 DF) in spring, to coincide with new growth, plus two additional sprays in autumn. The feasibility of autumn applications needs to be investigated further. In California, Teviotdale et al. (1989) detected copper residues in olives up to 115 d after a single fungicide application in autumn. Before final control recommendations be made, fungicide decay curves and residue levels in fruit and oil need to be established under New Zealand conditions for the most effective fungicides identified in this study.
Oct. 2004 Apr. 2005 Assessment date
Sept. 2005
Acknowledgements
Canterbury I Control 2 × KK 4 × Cs 6 × Cs
80 60 40 20 0 Jun. 2004
Disease incidence (%)
100 80
1341
Blenheim I Control 2 × KK 4 × Cs 6 × Cs
60 40 20 0 Jun. 2004
Fig. 3. Effects of the KK mixture or varying numbers of applications of copper sulphate (Cs) on olive leaf spot incidence at Canterbury Grove I and Blenheim Grove I. Control ¼ unsprayed; 2 KK ¼ the KK mixture applied to two trees from each control plot twice in autumn 2005; 4 Cs ¼ Cs applied four times across winter and spring of 2004; 6 Cs ¼ Cs applied six times across winter, spring and autumn of 2004/05. Bars represent the standard errors of the means.
rainfall in the Auckland region (Fig. 1) may result in greater washoff of fungicides, particularly contact fungicides, and thus more frequent fungicide applications may be required here than in drier regions. In Mediterranean regions, such as Italy and Spain, three fungicide applications (winter end, summer end and late autumn) are recommended (Graniti, 1993). In Californian olive groves, Wilson and Miller (1949) observed that a single spray of copper sulphate (Bordeaux mixture) gave satisfactory control of OLS when applied prior to protracted rains in autumn or early winter. Teviotdale et al. (1989) also reported that one application of a copper-containing fungicide in autumn before rain began was sufficient to effectively control the disease in Californian olive groves. However, our study demonstrated that under environmental conditions prevalent in New Zealand, winter-only applications were insufficient for effective control. Four applications in spring and autumn gave good control of OLS under New Zealand field conditions, but further research is required to determine how many applications of which fungicides are likely to provide optimum control. Investigations should also be conducted into optimum timing with respect to rainfall events and flushes of new leaves. In Californian olive groves, OLS incidence rarely exceeded 10% (Teviotdale and Sibbett, 1995), whereas disease
Funding for this research was provided by the New Zealand Foundation for Research, Science and Technology and the New Zealand Olive Association. Fungicides tested in the study were provided by: BASF New Zealand Limited, Du Pont New Zealand Limited, Syngenta Crop Protection Limited and Nufarm Limited. We would like to thank Margaret Auger and Candice Barclay, Lincoln University, for assisting with disease assessments. Our thanks also go to Cynthia Christie for her assistance in applying the fungicides in Canterbury Grove I. References Azeri, T., 1993. Research on olive leaf spot, olive knot and Verticillium wilt of olive in Turkey. EPPO Bull. 23, 437–440. Bourbos, V.A., Skoudridakis, M.T., 1993. Efficacite de quelgues fongicides cupriques a` l’e´gard de Spilocaea oleagina. EPPO Bull. 23, 393–397. Dahmen, H., Staub, T., 1992. Protective, curative, and eradicant activity of difenoconazole against Venturia inaequalis, Cercospora arachidicola, and Alternaria solani. Plant Dis. 76, 774–777. Graniti, A., 1993. Olive scab: a review. EPPO Bull. 23, 377–384. Gupta, G.K., Kumar, J., 1985. Studies on the curative (after infection) and eradicant (post-symptom) activity of fungicides against apple leaf infection by Venturia inaequalis. Pesticides 19, 18–20. Iannotta, N., Monardo, D., Perri, L., 2002. Effects of different treatments against Spilocaea oleagina (Cast.) Hugh. Acta Hortic. 586, 741–744. Knight, S.C., Anthony, V.M., Brady, A.M., Greenland, A.J., Heaney, S.P., Murray, D.C., Powell, K.A., Schulz, M.A., Spinks, C.A., Worthington, P.A., Youle, D., 1997. Rationale and perspectives on the development of fungicides. Annu. Rev. Phytopathol. 35, 349–372. MacDonald, A.J., Walter, M., Trought, M., Frampton, C.M., Burnip, G., 2000. Survey of olive leaf spot in New Zealand. NZ Plant Prot. 53, 126–132. Miller, H.N., 1949. Development of the leaf spot fungus in the olive leaf. Phytopathology 39, 403–410. Obanor, F.O., Walter, M., Jones, E.E., Jaspers, M.V., 2005a. Sources of variation in a field evaluation of the incidence and severity of olive leaf spot. NZ Plant Prot. 58, 273–277.
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Obanor, F.O., Walter, M., Jones, E.E., Jaspers, M.V., 2005b. In vitro effects of fungicides on conidium germination of Spilocaea oleagina, the cause of olive leaf spot. NZ Plant Prot. 58, 278–282. Obanor, F.O., Walter, M., Jones, E.E., Jaspers, M.V., 2008. Effect of temperature, relative humidity, leaf wetness and leaf age on Spilocaea oleagina conidium germination on olive leaves. Eur. J. Plant Pathol. 120, 211–222. Olive New Zealand, 2004. Best Practices for Olive Growing in New Zealand (IOP Manual) /http://www.olivesnz.org.nz/Growing_Olives.cfmS. Prota, U., 1995. Le malattie dell’olivo. Inform. Fitopatol. 45, 16–26. Saad, A., Masri, S., 1978. Epidemiological studies on olive leaf spot incited by Spilocaea oleagina (Cast.) Hugh. Phytopathol. Mediterr. 17, 170–173. Shabi, E., Birger, R., Lavee, S., 1994. Leaf spot (Spilocaea oleaginea) on olive in Israel and its control. Acta Hortic. 356, 390–394. Teviotdale, B.L., Sibbett, G.S., 1995. Consistent annual treatment helps future olive leaf spot control. Calif. Agric. 49, 27–32.
Teviotdale, B.L., Sibbett, G.S., Harper, D.H., 1989. Control of olive leaf spot by copper fungicides. Appl. Agric. Res. 4, 185–189. Thakur, V.S., Gupta, G.K., Garg, I.D., 1992. Effect of post-infection application of fungicides on the apple scab pathogen, Venturia inaequalis (Cke.) Wint. J. Phytopathol. 135, 160–166. Verona, O., Gambogi, P., 1964. On the characteristics of oil produced by olives attacked by Cycloconium oleaginum. Agric. Ital. 64, 1135–1139. Viruega, J.R., Trapero, A., 2002. Efficacy of kresoxim-methyl against olive leaf spot caused by Spilocaea oleagina. Acta Hortic. 586, 801–804. Wilson, E.E., Miller, H.N., 1949. Olive leaf spot and its control with fungicides. Hilgardia 19, 1–24. Ypema, H.L., Gold, R.E., 1999. Kresoxim-methyl: modification of a naturally occurring compound to produce a new fungicide. Plant Dis. 83, 4–19.
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Greenhouse and field evaluation of fungicides for control of olive leaf spot in New Zealand Friday O. Obanor a,, Marlene V. Jaspers a, E. Eirian Jones a, Monika Walter b a b
Bio-Protection and Ecology Division, Lincoln University, P.O. Box 84, Canterbury, New Zealand HortResearch, P.O. Box 51, Lincoln, Canterbury, New Zealand
a r t i c l e in fo
abstract
Article history: Received 10 December 2007 Received in revised form 29 April 2008 Accepted 29 April 2008
Olive leaf spot, a major disease of olive worldwide, is difficult to control in regions with cool and moist weather conditions such as New Zealand. The fungicides, boscalid, captan, carbendazim, copper hydroxide, copper sulphate, difenoconazole, dodine, kresoxim-methyl and a kresoxim-methyl/copper hydroxide mixture, were tested for efficacy in greenhouse and field trials. Greenhouse studies showed that all fungicides significantly reduced disease severity but the level of control was affected by the time interval between fungicide application and pathogen inoculation. For the field study, trees in commercial olive groves in three regions received two fungicide applications in each of three consecutive seasons: winter, spring and autumn. Fungicide type and time of application affected the disease incidence on the leaves. In winter, none of the fungicides, except copper sulphate and copper hydroxide, reduced disease incidence on the leaves compared with unsprayed controls. Most of the fungicides reduced disease incidence after spring and autumn applications, with the autumn applications being the most effective. Of the fungicides tested, copper sulphate and a mixture of kresoxim-methyl and copper hydroxide were the most effective, reducing disease incidence by 85–96% and 63–93%, respectively. Fungicide efficacy was greater in the drier climatic regions of New Zealand than the wetter regions. The results of this research facilitated the development of an improved fungicide spray programme for control of olive leaf spot in New Zealand. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Olives Spilocaea oleagina Peacock spot Cycloconium leaf spot Fungicides
1. Introduction Olive leaf spot (OLS), also known as peacock spot or Cycloconium leaf spot, is caused by the fungus Spilocaea oleagina (Castagne) Hughes. The disease causes severe premature defoliation of olive (Olea europaea L.), and sometimes leads to twig death (Miller, 1949; Azeri, 1993). Infection of fruit can cause unacceptable blemishes on table olives, and when it occurs on oilproducing cultivars, infection may cause a delay in ripening and a decrease in oil yields (Verona and Gambogi, 1964). The disease is common worldwide and serious in cooler olive-growing regions, with yield losses estimated to be as high as 20% (Wilson and Miller, 1949). In New Zealand, S. oleagina infection occurs during autumn through to early spring and the pathogen is dormant during hot, dry summers (Obanor et al., 2005a). S. oleagina survives during summer as mycelium in the lesions on living leaves. In autumn, the margins of these lesions expand into adjacent healthy tissues
Corresponding author. Current address: CSIRO Plant Industry, 306 Carmody Road, St. Lucia, QLD 4067, Australia. Tel.: +617 32142913; fax: +617 32142920. E-mail address: [email protected] (F.O. Obanor).
0261-2194/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2008.04.007
from where conidia are produced and then dispersed by rain splash and run-off (Miller, 1949). Moist weather conditions favour S. oleagina sporulation, conidium germination and infection, and young olive leaves are more susceptible to infection than older ones (Graniti, 1993). Obanor et al. (2008) reported that conidium production was optimal at 15 1C and under high humidity (100%), whereas conidium germination and infection required continuous free moisture for 12–24 h and temperatures ranging from 5 to 25 1C. These conditions are common in New Zealand olive groves, particularly in autumn and early spring when new leaves are formed. Application of copper-based fungicides is the main method of OLS control throughout olive-growing regions of the world (Teviotdale et al., 1989; Graniti, 1993). Timing of the fungicide applications is vital for effective control of OLS (Graniti, 1993). In the Mediterranean region, fungicides are usually applied before the onset of the main infection periods, which often coincide with the main shoot-growth seasons (spring and/or autumn) (Prota, 1995). In Californian olive groves, Teviotdale et al. (1989) reported that one annual application of copper-containing fungicides in late autumn, before the rainy period, effectively controlled OLS under low disease pressure. However, in New Zealand olive groves, multiple applications of copper-containing and/or
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systemic fungicides are commonly used annually, but often fail to provide effective control, resulting in very high disease levels in some regions (MacDonald et al., 2000). Apple scab, caused by Venturia inaequalis, has been successfully controlled by systemic fungicides such as carbendazim, difenoconazole and fenarimol (Dahmen and Staub, 1992). Given that S. oleagina and V. inaequalis are closely related and have similar modes of infection (Graniti 1993), it is likely that fungicides which control V. inaequalis could be effective in controlling OLS. An in vitro evaluation using fungicides known to be effective against V. inaequalis showed that the systemic fungicides, carbendazim and kresoxim-methyl, have the potential to effectively inhibit conidium germination and germ tube growth of S. oleagina (Obanor et al., 2005b). These fungicides are more target-specific than contact fungicides such as captan and copper-containing fungicides, and may also have a curative effect when applied within 10 d of infection (Viruega and Trapero, 2002). In Israel, Shabi et al. (1994) reported that 89–95% of the leaves on olive trees treated in autumn with a mixture of difenoconazole (Score 25 EC) and mineral oil (Texaco Spraytex CT774) were free from OLS when assessed the following spring, whereas only 66–82% of the leaves from trees treated with copper sulphate (Bordeaux Mixture) were free from the disease. This research investigated the rate, number and timing of different fungicides for their effectiveness in controlling OLS under field conditions in New Zealand.
dazim) (MacDonald et al., 2000). To evaluate the protective and/or curative activity of the fungicides, they were applied to the whole plants 0, 1, 3 or 7 d before or 1, 3 or 7 d after S. oleagina inoculation. Fungicides were applied with a hand-held spray bottle until runoff, using a volume of 10–15 ml per plant. For the day-0 treatment, sprayed plants were allowed to dry for 2 h prior to inoculation. On the day of inoculation (day 0), a suspension of 5.0 104 S. oleagina conidia ml1 was made by washing conidia from naturally infected olive leaves (cv. Barnea) as described by Saad and Masri (1978). The suspension was sprayed onto plants using an atomizer to just before run-off. For the next 7 d, the plants were enclosed within a clear polythene tent constructed inside the greenhouse to increase relative humidity and provide sufficient moisture for infection. For the fungicide applications 1 and 3 d post inoculation, the plants were treated and returned to the tent. However, the 7-d post-inoculation treatment was applied 30 min before all plants were transferred to the shadehouse for disease symptoms to develop. The mean daily temperature in the shadehouse ranged from 10 to 15 1C and moisture was supplied by an overhead misting system that operated for 10 min per day. There were four replicate plants for each treatment combination (products and application times), a total of 280 plants, which were arranged in a completely randomized design. After 12 weeks, the mean number of lesions per leaf was assessed for the six leaves marked at the time of inoculation. Lesion number per leaf had previously been shown to be a good estimate of disease severity (Obanor et al., 2005a). The experiment was conducted twice.
2. Materials and methods 2.1. Greenhouse experiments
2.2. Field trials
The experiment was conducted on 1–2-year-old olive plants of the cultivar ‘Barnea’, which is highly susceptible to OLS (Graniti, 1993). The plants were grown individually in 1 l plastic pots containing a mixture of composted bark and pumice (4:1, v/v) with slow release fertilizer (N:P:K ¼ 15:4:7.5) in a greenhouse maintained at 2275 1C and 30–60% RH. The youngest six fully expanded leaves were marked at the beginning of the trial. The fungicides used for the trial (Table 1) were those that had demonstrated high efficacy in controlling OLS in the in vitro assays (kresoxim-methyl, boscalid and captan) (Obanor et al., 2005b) and those commonly used for OLS control in New Zealand (copper sulphate, difenoconazole, copper hydroxide, dodine and carben-
Field trials were conducted in commercial olive groves in three regions: Canterbury (C), Blenheim (B) and Auckland (A). Two groves (I and II) from each region were selected, each of which had a history of OLS and had trees that were 6–8 years old and spaced on a 6 6 m grid. The Canterbury and Blenheim groves contained ‘Barnea’ trees, whereas in Auckland, the groves contained cultivar ‘Picual’. Methods of fertilizer application, irrigation and other cultural practices were similar for all groves and followed the standard procedures described in the New Zealand manual for commercial olive growers’ (Olive New Zealand, 2004). Temperature and rainfall data were collected for each region throughout the duration of the trials.
Table 1 Fungicide treatments used for the greenhouse (G) trial in Canterbury and the field trials (F) in Auckland (A), Blenheim (B) and Canterbury (C) Experiment Region Treatment
Product name and formulation
A.i. conc.a (g kg1)
Product rate (l1 water)
Supplier
G G, F G, F G G, F F F
Water B Boscalid A, B, C Captan Carbendazim C Copper hydroxide C Copper hydroxide C Copper hydroxide
– Endura 50 WG Crop Care Captan WG Bavistins DF ChampTM DP (rate 1) ChampTM DP (rate 2) Kocide 2000 DF
– 700 800 500 375 375 350
– 0.1 g 1.25 g 0.16 g 1.75 g 2.5 g 1.9 g
G, F G, F
A, B, C Copper sulphate A, B, C Difenoconazole
Cuprofixs Disperss Scores 10 WG
200 100
5g 0.25 g
G G, F G, F
Dodine A, B, C Kresoxim-methyl B, C Kresoxim-methyl/copper hydroxide (KK mixture)
Dodine 400 Strobys WG Strobys WG/ Kocide 2000 DF
400 500 500 350
0.18 ml 0.1 g 0.05 g 0.95 g
– BASF NZ Ltd. Nufarm Ltd. BASF NZ Ltd. Nufarm Ltd. Nufarm Ltd. Du Pont and Elliott Chemicals Nufarm Ltd. Syngenta Crop Protection Ltd. Nufarm Ltd. BASF NZ Ltd. BASF NZ Ltd. Du Pont and Elliott Chemicals
a
A.i. ¼ active ingredient concentration.
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Each fungicide treatment was applied to four-tree plots, all plots arranged in a completely randomized block design, replicated in five blocks for all groves. Each plot was separated from the next one in the row by one to five buffer trees (depending on the grove and layout) and from the plots in adjacent rows by one buffer row. Controls comprised plots of unsprayed trees. Each fungicide was applied twice in winter 2004, spring 2004 and autumn 2005 (Table 2), using growers’ spray equipment comprising hydraulic boom sprayer fitted with hollow-cone nozzles. Treatments were applied with water volumes of 1000–1200 l ha1, depending on the size of the trees. No other fungicides were sprayed on the trial trees, but all other normal grower practices were performed throughout the duration of the trials. In all groves, the fungicides, captan, kresoxim-methyl, difenoconazole or copper sulphate, were tested at the rates specified in Table 1. However in Canterbury and Blenheim, copper hydroxide, a kresoxim-methyl and copper hydroxide mixture (KK mixture) and boscalid were also included in the trial (Table 1). The effect of fungicide application in autumn was determined by applying a selected treatment to a subset of trees within the experimental plots. The autumn 2005 applications occurred in the same groves and trial plots used for winter and spring 2004 except that each four-tree trial plot was halved, resulting in a split-plot design, with half of the trees (randomly selected) receiving only two applications in winter and spring and the other half receiving two additional applications in autumn. The efficacy of a KK mixture was tested only in spring 2004 and autumn 2005 in Canterbury (Grove I) and in autumn 2005 in both Table 2 Sites, cultivars, application and assessment dates for field trials in 2004–2005 Region
Grove
Cultivar
Season
Application dates
Canterbury
I
Barnea
Winter
09 Jul. 2004 21 Jul. 2004 04 Nov. 2004 18 Nov. 2004 05 Apr. 2005 19 Apr. 2005 11 Jul. 2004 21 Jul. 2004 07 Nov. 2004 17 Nov. 2004 10 Apr. 2005 20 Apr. 2005
Spring Autumn II
Barnea
Winter Spring Autumn
Blenheim
I
Barnea
Winter Spring Autumn
II
Barnea
Winter Spring Autumn
Auckland
I
Picual
Winter Spring Autumn
II
Picual
Winter Spring Autumn
a
20 Jul. 2004 03 Aug. 2004 02 Nov. 2004 12 Nov. 2004 29 Apr. 2005 13 May. 2005 20 Jul. 2004 03 Aug. 2004 02 Nov. 2004 12 Nov. 2004 29 Apr. 2005 13 May 2005 31 Jul. 2004 13 Aug. 2004 01 Nov. 2004 10 Nov. 2004 03 Apr. 2005 12 Apr. 2005 01 Aug. 2004 14 Aug. 2004 17 Oct. 2004 27 Oct. 2004 30 Apr. 2005 14 May 2005
1337
groves in Blenheim. In Canterbury, KK mixture was applied to four-tree plot replicated in five blocks in spring 2004 but in autumn 2005, the fungicide was applied to two randomly selected trees from each control plot at both sites. Disease was evaluated at the beginning of the trial (June 2004), 2–3 months later in spring and then 4–5 months after the autumn treatments as shown in Table 2. On each occasion, one branch per tree was randomly selected on the south side at eye level. On this branch, 100 fully expanded matured leaves were removed and evaluated for disease incidence, which was expressed as the percentage of infected leaves.
2.3. Statistical analysis All data were subjected to analysis of variance (ANOVA) to evaluate the effect of treatment, time of application and their interaction. For the greenhouse data, there was homogeneity of error variances and so the data for the two experimental repeats were combined. However, due to heterogeneity of error variances in the field trials, data for each region and grove were analysed separately. Disease incidence was transformed to relative disease incidence compared with the untreated control, which was assigned a value of 100. Treatment means were compared using Fisher’s unprotected least significant difference test at the 5% probability level. Histograms, normal probability and scatter plots of the residuals were examined and there was no evidence of violation of the assumptions underlying the models used for ANOVA. All statistical analyses were conducted using Genstat 9.0 (Lawes Agricultural Trust, Rothamsted Experimental Station, Harpenden, UK).
Assessment dates
3. Results 12 Oct. 2004
3.1. Greenhouse experiments 20 Apr. 2005 10 Sept.2005 11 Oct.2004 20 Apr. 2005 10 Sept. 2005
19 Oct. 2004 16 Apr. 2005 02 Sept. 2005 19 Oct. 2004 16 Apr. 2005 –a
10 Oct. 2004 31 Mar. 2005 15 Sept. 2005
The main effects of treatment, time and the treatment time interaction were highly significant (Po0.001), and the means of experimental repeats did not differ significantly (P ¼ 0.326). At 12 weeks after inoculation, all plants that had received fungicides had significantly fewer leaf lesions than untreated control plants, for all application times except for dodine applied 7 d before pathogen inoculation (Table 3). When fungicides were applied before pathogen inoculation, the pre-inoculation interval did not affect numbers of leaf lesions per plant for most fungicides except for carbendazim, difenoconazole and kresoxim-methyl whose efficacy varied across the interval, and was generally greater if applied near the inoculation time. When fungicides were applied after inoculation, there was a reduction in efficacy after 3 d for captan, difenoconazole, copper hydroxide and copper sulphate and after 7 d for all other fungicides. The most effective fungicides were copper sulphate, kresoxim-methyl and KK mixture, all of which reduced disease severity by 74–99% when applied up to 7 d before inoculation and 1 d after inoculation (Table 3). The least effective fungicide was dodine, which reduced disease severity in the range 13–57% over the same period.
3.2. Field trials
10 Oct. 2004 31 Mar. 2005 15 Sept. 2005
Data were not collected from the trees because they had been removed.
Temperature and rainfall data collected for each region during the period of the trial, April 2004 through September 2005, are shown in Fig. 1. The average daily temperature in Auckland, Blenheim and Canterbury ranged from 6 to 23 1C, 3 to 24 1C and 2 to 23 1C, respectively. The total amount of rainfall recorded in
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Table 3 Olive leaf spot severity 12 weeks after inoculation with S. oleagina conidia and treatment at various times relative to the inoculation event Fungicidea
Control Boscalid Captan Carbendazim Copper hydroxided Copper sulphate Difenoconazole Dodine Kresoxim-methyl KK mixture LSDc (Po0.05)
Disease severityb
LSDc
Days before inoculation
Days after inoculation
7
3
1
0
1
3
7
82 32 36 63 19 5 55 71 21 5 14.2
82 19 29 45 22 3 49 65 16 2 12.1
88 25 24 51 25 5 34 61 5 3 10.7
89 18 26 19 20 2 29 57 10 1 9.9
96 14 23 21 27 6 22 41 8 4 11.3
86 23 36 34 56 59 38 44 13 3 13.8
94 50 59 67 62 70 74 71 24 6 16.1
(Po0.05)
20.9 13.3 10.5 15.6 14.9 8.0 12.9 13.7 7.5 3.2
the mean disease incidence being reduced by 64–96%. Overall, the most consistent and effective fungicides were the KK mixture and copper sulphate. By the end of the trials, these two treatments had reduced disease incidence by 85–96% and 63–93%, respectively, in all the groves except in Auckland (Grove II) in which copper sulphate failed to control the disease. The effects of additional fungicide applications in autumn are shown in Fig. 3. For those fungicides that were shown to be effective in spring in all groves, two additional sprays in the following autumn significantly (Po0.001) reduced disease incidence (Fig. 3). In Canterbury Grove I, for example, disease incidence was approximately 25% on trees that received six applications of copper sulphate over three seasons, compared with about 65% incidence for those that received four applications across winter and spring 2004 (Fig. 3). In addition, two applications of kresoxim in autumn only significantly (Po0.001) reduced disease incidence compared with the control in both Canterbury Grove I and Blenheim Grove I.
a
Fungicide application rates are shown in Table 1. Mean number of leaf lesions per plant (six leaves per plant and four plants per treatment) averaged over the two experimental repeats. c Least significant difference. d Fisher’s unprotected least significant difference (LSD). b
Canterbury and Blenheim was 811 and 1320 mm, respectively, whereas in Auckland a total of 1580 mm was recorded. Disease progression on unsprayed trees in Auckland, Canterbury and Blenheim olive groves during 2004 and 2005 is shown in Fig. 2. At all sites, with the exception of Grove II in Auckland, there was a progressive increase in disease incidence in untreated plots throughout the season, with the most rapid increase occurring over the winter months (April and September). In several groves, OLS incidence reached 100% and total defoliation occurred soon after, with 100% fruit infection and zero yields observed in the Canterbury and Auckland regions. The incidence of OLS in the experimental groves sprayed with different fungicides at different times is shown in Table 4. The main effects of treatment, time and the treatment time interaction were highly significant (Po0.001) under field conditions, but differed between groves and regions. The relative performance of individual fungicides also differed according to the timing of application as indicated by the significant treatment and application time interaction. In winter 2004, two applications of each fungicide generally resulted in a small and non-significant reduction in disease incidence when compared with the unsprayed control in all the groves. The exceptions were copper as copper sulphate (Cuprofixs disperss) and copper hydroxide (ChampTM DP: 2.5 g l1) applied in Canterbury, and kresoxim-methyl in Blenheim (Grove II), where there was a small but significant (Po0.05) reduction in disease incidence. There was high disease incidence on all trees, resulting in severe defoliation of the trees in all groves irrespective of the treatment. In addition, leaf tissue damage was observed on trees treated with copper-containing fungicides in all groves, particularly in Canterbury groves, indicating copper phytotoxicity. The efficacy of the various fungicides (Table 4) varied according to the regions, being most effective overall in Blenheim, where the disease pressure was lowest. In spring 2004 and autumn 2005, a tank mix of kresoxim-methyl (Strobys WG) and copper hydroxide (Kocide 2000 DF), which were used in only one Canterbury grove and one Blenheim grove provided the best OLS control, although this treatment was not statistically different from copper sulphate. At all other groves, copper sulphate was the most effective single fungicide. For the autumn 2005 applications, all the fungicides were highly effective in Blenheim Grove I, with
4. Discussion In the greenhouse trial, fungicides representing seven chemical classes reduced OLS severity on olive foliage when applied from 7 d before to 3 d after inoculation. Copper sulphate, kresoximmethyl and KK mixture were the most effective in protecting young olive leaves from OLS infection. In a previous study, Obanor et al. (2005b) reported that kresoxim-methyl and captan were effective in inhibiting conidium germination but the two coppercontaining fungicides, copper hydroxide and copper sulphate, were ineffective, which suggests that copper sulphate may act through means other than by inhibition of germination. Generally, all the fungicides provided protective and curative activity against OLS for up to 3 d after inoculation, possibly because of the slow growth of the pathogen (Obanor et al., 2008). The curative effect of kresoxim-methyl alone or in a copper mixture persisted 7 d after inoculation. This result was consistent with that of Viruega and Trapero (2002) who showed that mixing kresoxim-methyl with cupric or organocupric fungicides significantly reduced OLS severity up to 10 d after inoculation. A similar result was also reported for the closely related pathogen V. inaequalis (Ypema and Gold, 1999), eccept for dodine which showed high curative activity against the apple scab fungus, V. inaequalis when applied 48 or 144 h after inoculation (Gupta and Kumar, 1985; Thakur et al., 1992), but was relatively ineffective against OLS. The curative activity of a fungicide is related to its mode of action, the efficacy of its absorption and distribution within the leaf, and the position and mass of the invading pathogen. The low efficacy of difenoconazole, dodine and carbendazim, which are known to have curative, systemic activity against V. inaequalis (Ypema and Gold, 1999) might have been due to inadequate levels of active ingredients being absorbed by olive leaves. In vivo screening is considered to be a robust and relevant strategy for determining fungicide performance in the field, particularly with systemic fungicides (Knight et al., 1997). In this study, the efficacy of most fungicides was less in the field than in the greenhouse but ranking of fungicide effectiveness was similar. Overall, the copper-containing fungicides (some with kresoximmethyl) were the most effective, which supports the common usage of copper-containing fungicides, including copper sulphate, copper oxychloride, copper hydroxide and copper oxide in olivegrowing regions, such as California, Greece and Italy (Wilson and Miller, 1949; Bourbos and Skoudridakis, 1993; Teviotdale and Sibbett, 1995; Iannotta et al., 2002). Difenoconazole has been shown to have both protective and curative activity against
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25 Auckland
1339
Rain Temperature
80 70
20
50
15
40 10
Rain (mm)
Temperature (°C)
60
30 20
5 10 0 0 1-May-04 1-Jul-04 1-Sep-04 1-Nov-04 1-Jan-05 1-Mar-05 1-May-05 1-Jul-05 1-Sep-05 25 Blenheim
Rain Temperature
80 70
20
50
15
40 10
Rain (mm)
Temperature (°C)
60
30 20
5 10 0 0 1-May-04 1-Jul-04 1-Sep-04 1-Nov-04 1-Jan-05 1-Mar-05 1-May-05 1-Jul-05 1-Sep-05 25 Canterbury
Rain Temperature
80 70
20
15
50 40
10
Rain (mm)
Temperature (°C)
60
30 20
5 10 0 0 1-May-04 1-Jul-04 1-Sep-04 1-Nov-04 1-Jan-05 1-Mar-05 1-May-05 1-Jul-05 1-Sep-05 Fig. 1. Daily rainfall and average daily temperature in Auckland, Blenheim and Canterbury from 1 May 2004 to 30 September 2005.
V. inaequalis (Dahmen and Staub, 1992), but the efficacy of this fungicide in controlling OLS was not consistent, except in Blenheim groves where there was low disease pressure. In Israel, however, Shabi et al. (1994) reported that difenoconazole was
more effective than copper-containing fungicides, particularly when it was mixed with petroleum oil. They found that when olive trees were treated in autumn with difenoconazole (Score 25 EC) mixed with oil, 89–95% of the leaves were free from OLS when
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Auckland I Auckland II Canterbury I Canterbury II Blenheim I Blenheim II
Disease incidence (%)
100 80 60 40 20 0
Jun. 2004
Oct. 2004 Apr. 2005 Assessment date
Sept. 2005
Fig. 2. Mean olive leaf spot incidence in unsprayed trees in two commercial olive groves (I and II) in Canterbury, Blenheim and Auckland between 2004 and 2005. No data were collected for Blenheim Grove II in spring 2005 because the trees had been removed. Bars represent the standard errors of the means.
assessed 4–5 months later, whereas with copper sulphate, 66–82% of the leaves from treated trees were free of the disease. With another demethylation inhibitor fungicide, tebuconazole, Iannotta et al. (2002) reported that in Italy two applications in spring did not reduce S. oleagina infections compared with the controls. The inconsistencies in the reports may be attributed to differences in the environmental conditions, disease levels and timing of applications as this study indicated that autumn applications had the greatest overall effect on medium-term disease control. In this study, OLS incidence on untreated trees in commercial olive groves increased at a faster rate during the period April–September 2005 when compared with the winter period in the previous year, especially in Auckland and Canterbury. The weather conditions during these two periods were similar and unlikely to account for the differences in OLS incidence. The most probable reason for the rapid increase in disease levels in 2005 was inoculum build-up on trees which received no fungicides over the 15 months period of the trial. Efficacy of the fungicides tested in this study was greater in Canterbury and Blenheim than in Auckland. The poor performance of the fungicides in Auckland olive groves may be attributed to the environmental conditions being more favourable for OLS development (Graniti, 1993). In addition, the higher
Table 4 Olive leaf spot incidence on olive trees in commercial groves, which were sprayed with different fungicides and at different times in 2004 and 2005, relative to the unsprayed control treatment. Actual disease incidence values for the unsprayed controls are shown in parentheses Relative disease incidence2 (%) Canterbury
Blenheim
Auckland
Application time1
Fungicide
I
II
I
II
I
II
Jul. 2004 (Winter)
Control Copper sulphate Captan Difenoconazole Kresoxim-methyl Boscalid Copper hydroxide (Kocide 2000 DF) Copper hydroxide (ChampTM DP rate 1) Copper hydroxide (ChampTM DP rate 2) KK mixture
100a (25) 80b 95ab 88ab 90ab – 87ab 86ab 82b –
100a (39) 81b 90ab 96ab 88ab – – – – –
100a (12) 87a 91a 96a 87a 89a – – – –
100a (19) 84ab 82ab 81ab 78b 83ab – – – –
100a (25) 94a 92a 91a 94a – – – – –
100a (40) 82a 91a 90a 92a – – – – –
Nov. 2004 (Spring)
Control Copper sulphate Captan Difenoconazole Kresoxim-methyl Boscalid Copper hydroxide (Kocide 2000 DF) Copper hydroxide (ChampTM DP rate 1) Copper hydroxide (ChampTM DP rate 2) KK mixture
100a (39) 26ef 83bc 91ab 80bc – 73c 55d 33e 11f
100a (50) 33c 62b 80b 72b – – – – –
100a (18) 41c 74b 65b 56bc 60b – – – –
100a (32) 53c 65bc 70bc 73bc 83ab – – – –
100a (51) 81b 100a 86ab 100a – – – – –
100a (52) 100a 82a 84a 91a – – – – –
Apr. 2005 (Autumn)
Control Copper sulphate Captan Difenoconazole Kresoxim-methyl Boscalid Copper hydroxide (Kocide 2000 DF) Copper hydroxide (ChampTM DP rate 1) Copper hydroxide (ChampTM DP rate 2) KK mixture4
100a (100) 28ef 83bc 89ab 80bc – 49d 42de 23f 15f
100a (100) 25d 84ab 64c 67bc – – – – –
100a (48) 7cd 19c 14c 14c 36b – – – 4d
–3
100a (100) 37c 100a 94ab 76b – – – – –
100a (100) 100a 71b 89ab 69b – – – – –
1
– – – – – – – –
Treatments were applied twice in winter, spring and autumn using the same groves and trees. Application and assessment dates are shown in Table 2. Mean numbers of infected leaves per tree (100 leaves per tree and four trees per treatment plot). Means in a column within the same season followed by different letters are significantly different at P ¼ 0.05. 3 No data were collected for Blenheim Grove II because the trees were removed. 4 Treatment was applied to two randomly selected trees from each control plot. 2
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Disease incidence (%)
100
Oct. 2004 Apr. 2005 Assessment date
Sept. 2005
incidence of up to 100% can be found in New Zealand groves, where the environmental conditions (cool and wet) favour OLS development. Treatment history may also have cumulative effects on OLS severity in any given season. Spraying olives in one season might influence the amount of disease development the following season, either by causing a reduction in the inoculum levels in the trees or through the effect of fungicide residues which remain on the leaves until the next season. In this study, when the most effective fungicide, copper sulphate, was applied to trees in spring 2004 but not in autumn 2005, the fungicide was less effective on OLS when assessed in winter 2005 than the trees that also received the autumn applications. This is consistent with reports of Wilson and Miller (1949) and Teviotdale and Sibbett (1995), which showed that in Californian groves, OLS severity gradually decreased in trees treated annually. In addition, trees treated in 1 year had less OLS than non-treated trees in the subsequent year when all the trees were left untreated (Teviotdale and Sibbett, 1995). This study has shown that OLS in New Zealand groves can be controlled effectively by two applications of either copper sulphate (Cuprofixs Disperss) or a mixture of kresoxim-methyl (Strobys WG) and copper hydroxide (Kocide 2000 DF) in spring, to coincide with new growth, plus two additional sprays in autumn. The feasibility of autumn applications needs to be investigated further. In California, Teviotdale et al. (1989) detected copper residues in olives up to 115 d after a single fungicide application in autumn. Before final control recommendations be made, fungicide decay curves and residue levels in fruit and oil need to be established under New Zealand conditions for the most effective fungicides identified in this study.
Oct. 2004 Apr. 2005 Assessment date
Sept. 2005
Acknowledgements
Canterbury I Control 2 × KK 4 × Cs 6 × Cs
80 60 40 20 0 Jun. 2004
Disease incidence (%)
100 80
1341
Blenheim I Control 2 × KK 4 × Cs 6 × Cs
60 40 20 0 Jun. 2004
Fig. 3. Effects of the KK mixture or varying numbers of applications of copper sulphate (Cs) on olive leaf spot incidence at Canterbury Grove I and Blenheim Grove I. Control ¼ unsprayed; 2 KK ¼ the KK mixture applied to two trees from each control plot twice in autumn 2005; 4 Cs ¼ Cs applied four times across winter and spring of 2004; 6 Cs ¼ Cs applied six times across winter, spring and autumn of 2004/05. Bars represent the standard errors of the means.
rainfall in the Auckland region (Fig. 1) may result in greater washoff of fungicides, particularly contact fungicides, and thus more frequent fungicide applications may be required here than in drier regions. In Mediterranean regions, such as Italy and Spain, three fungicide applications (winter end, summer end and late autumn) are recommended (Graniti, 1993). In Californian olive groves, Wilson and Miller (1949) observed that a single spray of copper sulphate (Bordeaux mixture) gave satisfactory control of OLS when applied prior to protracted rains in autumn or early winter. Teviotdale et al. (1989) also reported that one application of a copper-containing fungicide in autumn before rain began was sufficient to effectively control the disease in Californian olive groves. However, our study demonstrated that under environmental conditions prevalent in New Zealand, winter-only applications were insufficient for effective control. Four applications in spring and autumn gave good control of OLS under New Zealand field conditions, but further research is required to determine how many applications of which fungicides are likely to provide optimum control. Investigations should also be conducted into optimum timing with respect to rainfall events and flushes of new leaves. In Californian olive groves, OLS incidence rarely exceeded 10% (Teviotdale and Sibbett, 1995), whereas disease
Funding for this research was provided by the New Zealand Foundation for Research, Science and Technology and the New Zealand Olive Association. Fungicides tested in the study were provided by: BASF New Zealand Limited, Du Pont New Zealand Limited, Syngenta Crop Protection Limited and Nufarm Limited. We would like to thank Margaret Auger and Candice Barclay, Lincoln University, for assisting with disease assessments. Our thanks also go to Cynthia Christie for her assistance in applying the fungicides in Canterbury Grove I. References Azeri, T., 1993. Research on olive leaf spot, olive knot and Verticillium wilt of olive in Turkey. EPPO Bull. 23, 437–440. Bourbos, V.A., Skoudridakis, M.T., 1993. Efficacite de quelgues fongicides cupriques a` l’e´gard de Spilocaea oleagina. EPPO Bull. 23, 393–397. Dahmen, H., Staub, T., 1992. Protective, curative, and eradicant activity of difenoconazole against Venturia inaequalis, Cercospora arachidicola, and Alternaria solani. Plant Dis. 76, 774–777. Graniti, A., 1993. Olive scab: a review. EPPO Bull. 23, 377–384. Gupta, G.K., Kumar, J., 1985. Studies on the curative (after infection) and eradicant (post-symptom) activity of fungicides against apple leaf infection by Venturia inaequalis. Pesticides 19, 18–20. Iannotta, N., Monardo, D., Perri, L., 2002. Effects of different treatments against Spilocaea oleagina (Cast.) Hugh. Acta Hortic. 586, 741–744. Knight, S.C., Anthony, V.M., Brady, A.M., Greenland, A.J., Heaney, S.P., Murray, D.C., Powell, K.A., Schulz, M.A., Spinks, C.A., Worthington, P.A., Youle, D., 1997. Rationale and perspectives on the development of fungicides. Annu. Rev. Phytopathol. 35, 349–372. MacDonald, A.J., Walter, M., Trought, M., Frampton, C.M., Burnip, G., 2000. Survey of olive leaf spot in New Zealand. NZ Plant Prot. 53, 126–132. Miller, H.N., 1949. Development of the leaf spot fungus in the olive leaf. Phytopathology 39, 403–410. Obanor, F.O., Walter, M., Jones, E.E., Jaspers, M.V., 2005a. Sources of variation in a field evaluation of the incidence and severity of olive leaf spot. NZ Plant Prot. 58, 273–277.
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Obanor, F.O., Walter, M., Jones, E.E., Jaspers, M.V., 2005b. In vitro effects of fungicides on conidium germination of Spilocaea oleagina, the cause of olive leaf spot. NZ Plant Prot. 58, 278–282. Obanor, F.O., Walter, M., Jones, E.E., Jaspers, M.V., 2008. Effect of temperature, relative humidity, leaf wetness and leaf age on Spilocaea oleagina conidium germination on olive leaves. Eur. J. Plant Pathol. 120, 211–222. Olive New Zealand, 2004. Best Practices for Olive Growing in New Zealand (IOP Manual) /http://www.olivesnz.org.nz/Growing_Olives.cfmS. Prota, U., 1995. Le malattie dell’olivo. Inform. Fitopatol. 45, 16–26. Saad, A., Masri, S., 1978. Epidemiological studies on olive leaf spot incited by Spilocaea oleagina (Cast.) Hugh. Phytopathol. Mediterr. 17, 170–173. Shabi, E., Birger, R., Lavee, S., 1994. Leaf spot (Spilocaea oleaginea) on olive in Israel and its control. Acta Hortic. 356, 390–394. Teviotdale, B.L., Sibbett, G.S., 1995. Consistent annual treatment helps future olive leaf spot control. Calif. Agric. 49, 27–32.
Teviotdale, B.L., Sibbett, G.S., Harper, D.H., 1989. Control of olive leaf spot by copper fungicides. Appl. Agric. Res. 4, 185–189. Thakur, V.S., Gupta, G.K., Garg, I.D., 1992. Effect of post-infection application of fungicides on the apple scab pathogen, Venturia inaequalis (Cke.) Wint. J. Phytopathol. 135, 160–166. Verona, O., Gambogi, P., 1964. On the characteristics of oil produced by olives attacked by Cycloconium oleaginum. Agric. Ital. 64, 1135–1139. Viruega, J.R., Trapero, A., 2002. Efficacy of kresoxim-methyl against olive leaf spot caused by Spilocaea oleagina. Acta Hortic. 586, 801–804. Wilson, E.E., Miller, H.N., 1949. Olive leaf spot and its control with fungicides. Hilgardia 19, 1–24. Ypema, H.L., Gold, R.E., 1999. Kresoxim-methyl: modification of a naturally occurring compound to produce a new fungicide. Plant Dis. 83, 4–19.