Susceptibility of several Japanese plum cultivars to pests and diseases in a newly established organic orchard

Scientia Horticulturae 123 (2009) 210–216

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Susceptibility of several Japanese plum cultivars to pests and diseases in a newly established organic orchard Pedro A. Garcı´a-Galavı´s a, Carmen Santamarı´a a, Juan A. Jime´nez-Bocanegra a, Laura Casanova b, Antonio Daza a,* a b

IFAPA Centro ‘‘Las Torres-Tomejil’’, Apdo. Oficial, 41200 Alcala´ del Rı´o (Sevilla), Spain Departamento de Ciencias Agroforestales, EUITA, Universidad de Sevilla, Sevilla, Spain

A R T I C L E I N F O

A B S T R A C T

Article history: Received 14 April 2009 Received in revised form 25 August 2009 Accepted 26 August 2009

The susceptibility of 14 Japanese plum cultivars to an aphid pest and three fungal diseases was analysed during 2007 and 2008 in two experimental orchards, one in organic and the other in conventional management. There was a significantly higher incidence of green peach aphids [Myzus persicae (Sulzer)] for most of the cultivars in the organically managed treatment. ‘Fortune’, ‘Primetime’, ‘Larry Ann’ and ‘Sapphire’ were the cultivars most affected, and ‘Souvenir’ suffered the lowest attack in both treatments. Shot hole disease (Wilsonomyces carpophilus) affected both orchards at low levels, and only two cultivars, ‘Santa Rosa’ and ‘Larry Ann’, suffered a moderate attack. Powdery mildew (Sphaerotheca pannosa) incidence was significantly higher in the conventionally managed orchard and only the ‘Red Beaut’ cultivar was affected. Rust disease (Tranzschelia spp.) incidence was significantly higher in the organic treatment. The cultivars in which the rust disease appeared earliest and reached the highest levels were ‘Showtime’, ‘Santa Rosa’, ‘Friar’, and ‘Larry Ann’. An intense rust infestation in leaves provoked a premature defoliation in the organic plot, indicating that proper control of this disease is important to maintain tree vigour and yield. ß 2009 Elsevier B.V. All rights reserved.

Keywords: Plum orchard Organic farming Aphids Shot hole Powdery mildew Rust

1. Introduction There are two well differentiated aspects of organic farming with respect to other agronomical systems: (1) fertilization is almost exclusively provided by organic compounds (compost, green manure), and (2) use of chemically synthesized substances to control of pests, diseases and weeds are forbidden (Lampkin, 2002). These premises lead to a specific type of crop management that can greatly influence yield and quality. These principles are also drivers of the key environmental benefits associated with organic agriculture (Feber et al., 1997; Reidsma et al., 2006). Organic farming has been regulated in Europe since 1991 (Council Regulation, EEC, No 2992/91 and Council Regulation, EC, No 834/2007). The region of Andalusia in southern Spain is one of the most important European areas for certified organic agriculture with about one million hectares in cultivation (MARM, 2009). The production of conventional or integrated stone fruit, especially nectarine, peach and plum, is important in the area, but cultivation of these fruits under organic management is nearly nonexistent mainly due to the difficulties related to the control of pests and diseases.

The most important pests affecting stone fruits in Andalusia are the Mediterranean fruit fly [Ceratitis capitata (Wiedemann)] (Garcı´aMarı´, 2003), several species of aphids, San Jose´ scale [Quadraspidiotus perniciosus (Comstock)], plum gall nut (Acalitus phloeocoptes) and the European red spider mite [Panonychus ulmi (Koch)] (Ogawa et al., 2000). In some areas and circumstances, the peach flatheaded rootborer [Capnodis tenebrionis (Linnaeus)] is also a serious threat (Viggiani, 1991). Some important fungal diseases affecting stone fruits in the region are shot hole (Wilsonomyces carpophilus), rust (Tranzschelia spp.), peach leaf curl (Taphrina deformans), powdery mildew (Sphaeroteca pannosa), and the mummified or moniliosis (Monilia spp.) (Montesinos et al., 2000; Haseli, 2004). The vast genetic plasticity and agronomical hardiness of plum make it a good culture for organic fruit production (Glucina et al., 1990). In this work we present preliminary comparative results examining organic and conventional management of a common pest, green peach aphids, and three fungal diseases, shot hole, powdery mildew and rust in this region. 2. Materials and methods 2.1. Plant material and experimental plot design

* Corresponding author. Tel.: +34 955045505; fax: +34 955045625. E-mail address: [email protected] (A. Daza). 0304-4238/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2009.08.017

Japanese plum cultivars used in this work are listed in Table 1. Classic cultivars such as ‘Santa Rosa’ or ‘Golden Japan,’ together

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Table 1 List of cultivars used in the study. Cultivar

Tree vigour/structure

Skin/flesh fruit colour

Ripening (week)

Source or reference

‘Larry Ann’ ‘Fortune’ ‘Souvenir’ ‘Songold’ ‘Sapphire’ ‘Red Beaut’ ‘Laetitia’ ‘Black Amber’ ‘Primetime’ ‘Santa Rosa’ ‘Angeleno’ ‘Golden Japan’ ‘Friar’ ‘Showtime’

Weakness/upright Moderate/semi Vigorous/open Vigorous/semi Moderate/semi Vigorous/open Moderate/semi Moderate/semi Moderate/upright Moderate/upright Vigorous/open Vigorous/open Moderate/upright Weakness/semi

Dark red/yellow Red/amber Dark red/orange-yellow Greenish-yellow/yellow Purple/light yellow Dark red/yellow Red/orange-yellow Dark purple/amber Purple-black/red Violet/yellow-red Black-violet/amber Yellow/yellow Dark purple/amber Reddish-purple/yellow

31–32 29–30 26–27 33–34 25–26 21–22 33–34 26–27 29–30 25–26 36–37 25–26 31–32 25–26

South Africa, 1995 USDA, 1971, Ramming and Tanner (1993) South Africa, 1993, ARC South Africa, 1970, ARC South Africa, 1992, ARC USA, 1985, ARC South Africa, 1985, ARC California, 1980 United States Patent PP09022, 1993 USA, Obtentor L. Burbank, 1907 USA, 1995 Duval (1999) USA, obtentor H. Weinberger, 1968 United States Patent PP08037, 1992

ARC: Agricultural Research Council Infruitec-Nietvoorbi, South Africa. USDA: United States Department of Agriculture.

with other more recent cultivars such as ‘Souvenir’ or ‘Primetime’ were included. Two similar experimental orchards, 5500 m2 each, were planted in the IFAPA Centro ‘‘Las Torres-Tomejil’’, located in the province of Seville (Southwest Spain), a traditional fruit tree culture region. The site has a silt loam soil with 5.06% active carbonate, 1.4% organic matter and a pH of 8.4. One orchard was managed using an organic system and the other following a conventional management system. Planting was performed in January, 2005 using bare-root, 1-year-old-plants grafted on Marianna GF 8-1 rootstock. The orchard design consisted of 18 trees of each variety, distributed in three blocks, 6 trees each. The framework of planting was 5 m  3.75 m with ‘Methley’ and ‘Pissardi’ cultivars, 9 trees each, uniformly distributed in each plot to be used as pollinators. 2.2. Agroclimatic conditions and management practices The study was carried out in 2007 and 2008. Agroclimatic conditions registered in the zone during the time of the study are shown in Fig. 1, using the Grapher V.7 software (Golden Software Inc.). A surface irrigation system was used through two parallel grooves on both sides of each tree row. The timing of irrigation was similar in both plots, with each receiving 7 and 6 irrigations throughout the summer in 2007 and 2008 (350,000 l ha 1 irrigation 1). Fertilization in the organic orchard consisted of animal-originated compost and green manure, and the convention-

ally managed plot received foliar applications of different vegetal compounds and mineral fertilizers. Soil and foliar analysis were conducted as described by Herencia et al. (2007). 2.3. Evaluation of pest and disease incidence and defoliation degree The incidence of pests and diseases was studied from April to October. Nine trees per cultivar (trees 1, 3 and 5 of each block) and treatment were observed and analysed weekly. One pest, green peach aphids, and three fungal diseases, shot hole, powdery mildew, and rust were screened. A 0–5 scale was used to register the incidence on leaves or shoots, according to the following scale: 0: no presence, 1: 1–20%, 2: 21–40%, 3: 41–60%, 4: 61–80% and 5: 81–100% coverage. Data represented in the figures are those of the sampling dates in which the pest or disease attack was more serious: green peach aphids (second week of June in 2007 and fourth week of May in 2008), shot hole (second week of July in 2007 and fourth week of September in 2008), powdery mildew (second week of September in 2008), rust (second week of October in 2007 and 2008). Defoliation degree was evaluated using a 0–5 scale and in some cases by determining the weight of leaves contained in 10 branches, 80 cm long each. Leaf water content was calculated after drying for 40 h at 90 8C. The control of pests and diseases was conducted according to regulations for both organic and conventional agriculture. Products, concentration and timing of treatments against pests and diseases in both orchards are shown in Table 2.

Fig. 1. Agroclimatic conditions registered in the study area during April to October in 2007 and 2008. Relative humidity and temperature are daily mean values.

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Table 2 Compounds, concentration and timing of treatments against pests and diseases in both plots along 2007 and 2008. Date

2007 February 19 April 16 May 18 June 11 June 19 July 10 July 26 September 3 November 27 2008 February 19 April 1 April 16 April 17 May 13 May 20 June 12 July 4 July 29 September 12 December 10

Products used in the two types of management

Pest o disease targeted

Organic

Conventional

Neem extract (0.15) Sulphur (0.4) C. verum extract (0.12) P. s. (1) P. s (1) Sulphur (0.4) E. arvense extract (0.5) E. arvense extract (0.5) Copper (0.3)

Pyriprox. (0.005) Sulphur (0.4) Imidacl. (0.01) – – Sulphur (0.4) Mancozeb (0.2) Mancozeb (0.2) Copper (0.3)

San Jose´ Scale Fungi, mites Aphids Aphids Aphids Fungi, mites Rust Rust Fungi, bacteria

Neem extract (0.15) Sulphur (0.4) Sulphur (0.4) P. s. (1) P. s. + 6% pyr (0.15) P. s. + 6% pyr (0.15) Sulphur (0.4) Sulphur (0.4) Sulphur (0.4) Sulphur (0.4) Copper (0.3)

Pyriprox. (0.005) Sulphur (0.4) Sulphur (0.4) Imidacl. (0.01) – – Sulphur (0.4) Mancozeb (0.2) – Cyproc. (0.001) Copper (0.3)

San Jose´ Scale Fungi, mites Fungi, mites Aphids Aphids Aphids Fungi, mites Rust Rust Rust Fungi, bacteria

The numbers in brackets indicate the concentrations (%) used. C. verum, Cinnamomun verum; Cyproc., Cyproconazole; E. arvense, Equisetum arvense; Imidacl., Imidacloprid; Pyriprox., Pyriproxyfen; P. s., Potassium soap; pyr, pyretrins.

2.4. Statistical analysis

3. Results

Statistical analyses were performed using Statistix software (version 9.0, NH Analytical Software, USA). Analysis of variance (ANOVA) was used to analyse the leaf fresh weight data. All other pairwise comparisons were performed with the Kruskal–Wallis nonparametric test at the P < 0.05 level of significance. Correlation between rust incidence and a premature fall of leaves was calculated using the rank correlation of Spearman.

3.1. Incidence of green peach aphids on the different cultivars In this region the green peach aphids are a common spring pest. The aphids appear in early spring, then progressively decline and disappear by the beginning of July when the temperature rises. In 2007, the green peach aphid attack was lower than in 2008. In both years pest incidence was significantly higher in the organically managed orchard (see Fig. 2A). Fig. 3 shows the averaged 2007–

Fig. 2. Global pest and disease incidence in 2007 and 2008 in the organically (dark bars) and conventionally (clear bars) managed orchards. In each year, different letters indicate that the means are significantly different at P < 0.05. LSD (least significant difference) values were: aphids 2007, 17.99, aphids 2008, 10.43, shot hole 2007, 17.99, shot hole 2008, 10.43, powdery mildew, 10.43, rust 2007, 17.99 and rust 2008, 10.43.

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Fig. 3. Average 2007–2008 green peach aphid incidence on different Japanese plum cultivars in an organically managed orchard. The length of the bars represents the pest level on the 0–5 scale. Numbers indicate the mean values in the Kruskal–Wallis test. Different letters indicate that the means are significantly different at P < 0.05. LSD, least significant difference.

Fig. 5. Average 2008 powdery mildew incidence on different Japanese plum cultivars in an organically managed orchard. The length of the bars represents the pest level on the 0–5 scale. Numbers indicate the mean values in the Kruskal–Wallis test. Different letters indicate that the means are significantly different at P < 0.05. LSD, least significant difference.

2008 susceptibility of the different cultivars in the organically managed orchard, and separate data from each year are presented in Appendix 1. Nearly all the cultivars were affected by the green peach aphids, but the incidence in ‘Fortune’, ‘Primetime’, ‘Larry Ann’ and ‘Sapphire’ was significantly higher than in ‘Golden Japan’ or ‘Souvenir’. Moderate pest control was obtained by the application of potassium soap containing 6% pyrethrins, but not with potassium soap alone (data not shown). In the conventional orchard the pests were controlled by the application of imidacloprid.

3.3. Powdery mildew

3.2. Shot hole disease Shot hole disease was not widespread in 2007, or in 2008, and no significant differences were observed between the levels reached in the organic and conventional orchards (Fig. 2B). In general, levels of shot hole disease were similar from June to September. Only ‘Santa Rosa’, and to a lesser extent ‘Larry Ann’, showed an appreciable sensitivity to the shot hole fungus. The other cultivars were not attacked at a substantial level by the fungus (Fig. 4). The data from 2007 and 2008 are separately presented in Appendix 2. Climatic conditions in late summer and early autumn of 2008 (Fig. 1) were conducive to fungal disease development and a slight increase in shot hole was observed in ‘Red Beaut’, ‘Songold’ and ‘Souvenir’. No specific treatments were carried out against this fungus.

Fig. 4. Average 2007–2008 shot hole incidence on different Japanese plum cultivars in an organically managed orchard. The length of the bars represents the pest level on the 0–5 scale. Numbers indicate the mean values in the Kruskal–Wallis test. Different letters indicate that the means are significantly different at P < 0.05. LSD, least significant difference.

In this area powdery mildew is not a serious disease in plum orchards—just a few cultivars are affected and only if weather conditions favour fungus development. Thus, during 2007 none of the cultivars were affected. In 2008, there was no infection in spring, but powdery mildew appeared in late summer and autumn. In September and October 2008, the relative humidity (65.1%) and rainfall (100.2 mm) were higher than in the same period in 2007 (62.3% and 36.2 mm). The overall infection rate was significantly higher in the conventional treatment (Fig. 2C). The cultivar ‘Red Beaut’ showed a clear susceptibility to this fungus, with a significantly higher infestation level than most other varieties (Fig. 5). Specific treatments against this fungus were cyproconazole in the conventionally managed orchard and wettable sulphur in the organically managed orchard. 3.4. Rust disease Overall, over the 2-year period, significantly higher levels of rust incidence were observed in the organic treatment (Fig. 2D). Statistical analysis of the average 2007 and 2008 values obtained at the moment of the highest level of rust attack in the organic orchard showed that ‘Showtime’ and ‘Friar’ were the cultivars with greatest sensitivity to rust, followed by ‘Larry Ann’ and ‘Santa Rosa’ (Fig. 6). ‘Souvenir’ and ‘Red Beaut’ were the cultivars less affected,

Fig. 6. Average 2007–2008 rust incidence on different Japanese plum cultivars in an organically managed orchard. The length of the bars represents the pest level on the 0–5 scale. Numbers indicate the mean values in the Kruskal–Wallis test. Different letters indicate that the means are significantly different at P < 0.05. LSD, least significant difference.

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Table 3 Soil and foliar composition in the two plots in September 2007. Treatment

Parameter N

P

Physico-chemical soil analysis Conventional 499 20.9 Organic 656 27.08 Cultivar

Foliar analysis ‘Golden Japan’ ‘Sapphire’ ‘Showtime’

Treatment

Conventional Organic Conventional Organic Conventional Organic

K

Ca

Mg

Na

Fe

Mn

Zn

B

E.C.

pH

O.M.

CaCO3

0.74 0.98

9.18 10.45

1.91 2.47

0.93 1.08

<5 <0.5

80 59.6

<2.5 <2.5

<0.5 <0.5

169 186

8.4 8.4

1.66 2.11

4.72 4.55

Parameter N

P

K

Ca

Mg

Na

Fe

Mn

Zn

B

Cu

Mo

S

Chlorides

2.94 2.48 2.58 2.78 2.62 2.09

0.19 0.16 0.15 0.21 0.24 0.26

1.80 1.69 2.08 1.92 2.58 3.21

1.74 2.50 3.03 1.31 2.05 3.01

0.43 0.53 0.59 0.42 0.44 0.63

<250 <250 <250 <250 <250 <250

249 316 334 289 270 370

192 292 309 162 356 214

26 41 51 24 56 35

13 11 <5 13 7 13

6 6 5 9 6 8

0.37 0.20 <0.1 <0.1 <0.1 <0.1

0.19 0.19 0.16 0.14 0.16 0.17

350 399 369 <300 <300 521

Units are given in % (O.M., CaCO3), mg/kg (N, P, Fe, Mn, Zn, B), meq/100 g (K, Ca, Na, Mg), mS/cm (E.C.). Units are given in % (N, P, S, Mg, K), mg/kg (Chlorides, Na, B, Fe, Mn, Cu, Mo), meq/100 g (Ca, Na, Mg), mS/cm (E.C.). Table 4 Rust incidence on leaves of the cultivar ‘Showtime’ in three different tree management. Parameter

Leaf fresh weight (g) Rust incidence (0–5) Defoliation (0–5)

Tree management

LSD

Organic

Conventional

Organic + chemical pesticide

19.77 b 4.17 (15.50 a) 4.00 (15.50 a)

148.57 a 1.50 (6.83 b) 1.33 (6.5 b)

119.83 a 1.50 (6.16 b) 1.50 (6.5 b)

32.97 (7.37) (7.37)

Data were obtained in October 2008. The numbers in brackets refer to the mean values through the Kruskal–Wallis test. Different letters in a same row indicate significant differences at P < 0.05. LSD, least significant difference.

and the rest of the cultivars presented an intermediate level of sensitivity. The data from 2007 and 2008 are separately presented in Appendix 3. In both years, rust attack began at the end of June or the first days of July and increased until the end of the vegetative period. During July and August, the disease progressed slightly only in a few susceptible varieties such as ‘Showtime’, ‘Friar’, ‘Santa Rosa’, ‘Larry Ann’ and ‘Sapphire,’ and then increased strongly through October and November, until the leaves fell. In the organic orchard, the disease progressed despite several attempts at treatment using sputtering Equisetum spp. excerpt and wettable sulphur. In the conventional plot, only the cultivars ‘Friar’, ‘Showtime’ and ‘Larry Ann’ suffered a moderate infection and that was suitably blocked by applications with mancozeb and cyproconazole. 3.5. Correlation between rust incidence and a premature fall of leaves in autumn In autumn 2006, a slightly early leaf fall was detected in the organically managed orchard. In October 2007, sampling was conducted in both plots to record the degree of leaf drop and the presence of rust. The results showed a high Spearman’ rank correlation (r = 0.611, P < 0.0000). A positive and high correlation between both parameters was also obtained in the sampling performed in October 2008 (r = 0.677, P < 0.0000). In fact, the ratio of conventional leaf weight/organic leaf weight was 2–5 and the water content was also higher in the leaves from the conventional treatment (data not shown). To determine if this early defoliation in the organically managed plot could be due to changes in soil content or foliar nutritional status, soil and foliar analysis were performed in both treatments in September 2007. The results are shown in Table 3, and indicate that there are no significant differences between the treatments. Rust disease appeared to be the most important cause of premature defoliation. For further evidence, in September–October 2008 six trees of ‘Showtime’ cultivar were chosen from the organic plot, 2 per block, and each was carefully sprayed once with mancozeb and after 25 days with cyproconazole. The results on rust level and defoliation

degree are shown in Table 4 and indicate that rust is likely the causal agent of premature defoliation in the organically managed plot.

4. Discussion The production of organic stone fruit (peach, nectarine, plum, apricot) is low mainly due to problems caused by pests and diseases (Weibel et al., 2007). So, research in this field could inject a degree of dynamism into this sector, and, in addition, foster values of food security and environmental safety, both strongly linked to the organic systems. We have evaluated the incidence of the green peach aphid pest and shot hole, powdery mildew and rust fungal diseases in two fields of 14 Japanese plum cultivars, comparatively handled in organic farming and conventional production. On our incidence scale (ranging from 0 to 5) values above 1 reflect an incidence higher than 20%, a level that causes physiological damage with important agronomic impact. Since all the cultivars suffered attacks of green peach aphids above 1, aphid action must be quickly blocked to avoid damage in foliage and new shoots that can depress the vigour of trees in a period of active vegetative growth. ‘Fortune’ and ‘Primetime’, two cultivars showing similar characteristics in tree structure and leaf texture, were the most affected. In recent years several authorized products in organic agriculture have been used to combat aphids. Karagounis et al. (2006) tested several products, including kaolin, mineral oil and potassium soap, on a plantation of peach trees. They found that all of the products were effective, particularly kaolin, but also noted a different response in the 2 years tested, 2003 and 2004, which they attributed to the interaction with climatic factors. Other authors have also verified the effectiveness of other products like neem extract (Tang et al., 2002), again kaolin (Marko´ et al., 2008), extract of pepper and natural pyrethrins (Edelson et al., 2002) and as a general conclusion, it seems that there are several products authorized in organic farming that when properly applied maintain aphid pests at levels low enough to permit the normal development of the crop. In our study, we

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obtained better control of aphids with the mixture of potassium soap + 6% natural pyrethrins. Shot hole highly affects some particular plum cultivars (Juan Luis Viveros, personal communication). Such is the case of ‘Santa Rosa’ and ‘Larry Ann’, included in our work, and in ‘Pioneer’ (Daza et al., 2008). No significant differences between the two types of management have been detected and this particular fungal disease does not present a serious problem in organic plum orchards for most of the cultivars. We observed a moderate attack of powdery mildew in summer and autumn of 2008, affecting only ‘Red Beaut’. In fact, this disease could be a serious problem in spring, since it may also affect fruits. A higher incidence has been observed in the conventionally managed plot, probably due to the preventive control exerted by more abundant sulphur applications in the organic one. A proper pruning in summer to ventilate the trees can also prevent the progression of this disease. In general, rust disease affects fruit trees in late summer and autumn in southern Spain. This study shows that ‘Larry Ann’ ‘Showtime’ and ‘Friar’ are the cultivars in which the disease appeared earlier and reached the highest values. It has been proven here that when leaves are severely infected (we found higher infestation levels in the organic plot) a premature defoliation can occur during early autumn that probably reduces tree vigour. Wettable sulphur has been frequently used against rust disease (Duruz and Goldsworthy, 1928; Michailides and Ogawa, 1986) but in our experiments we failed to adequately curb the progress of rust in the organically managed orchard with either of the two products tested, extract of Equisetum spp. and sulphur. So, new strategies of control that include a more precise timing of treatments or the use of new fungicides are necessary. The evaluation of azoxystrobin, a natural fungicide compound produced by Oudemansiella mucida and Strobilurus tenacellus, has been very effective in other regions and could be of interest (Soto-Estrada and Fo¨rster, 2003). From an agronomical point of view, it is essential to assess the performance of the different cultivated cultivars, with the aim of selecting the most resistant or tolerant to harmful agents. It would be also interesting to evaluate the effectiveness of approved control measures in organic farming. The study orchards are still very young and the study of both types of management covers only 3 years. Accordingly, the results presented in this study are still preliminary and will require further assays to assess the behaviour of different cultivars in organic orchards. However, it is beginning to be clear that cultivars such as ‘Showtime’, ‘Friar’, ‘Santa Rosa’ or ‘Larry Ann’ will be more problematic in organic management than the others, due to their high sensitivity to several common pests and diseases in plum orchards. By contrast, cultivars as ‘Souvenir’, ‘Red Beaut’ or ‘Golden Japan’ seem to be more resistant. Acknowledgements ˜ oz and J.L. Viveros for technical We are grateful to R. Mun assistance. The authors are also thankful to Orero Nursery private company for their aid and facilities in performing this study. Funding for this research was provided by the INIA-FEDER (Project RTA 2006-00054) and the IFAPA (Complementary aid FIC07-07). Appendix 1 2007 (upper) and 2008 (lower) green peach aphid incidence on different Japanese plum cultivars in an organically managed orchard. The length of the bars represents the pest level on the 0–5 scale. Numbers indicate the mean values in the Kruskal–Wallis test. Different letters indicate that the means are significantly different at P < 0.05. LSD, least significant difference.

215

Appendix 2 2007 (upper) and 2008 (lower) shot hole incidence on different Japanese plum cultivars in an organically managed orchard. The length of the bars represents the pest level on the 0–5 scale. Numbers indicate the mean values in the Kruskal–Wallis test. Different letters indicate that the means are significantly different at P < 0.05. LSD, least significant difference.

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Appendix 3 2007 (upper) and 2008 (lower) rust incidence on different Japanese plum cultivars in an organically managed orchard. The length of the bars represents the pest level on the 0–5 scale. Numbers indicate the mean values in the Kruskal–Wallis test. Different letters indicate that the means are significantly different at P < 0.05. LSD, least significant difference.

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