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Effect of banana spray oil on banana yield in the absence of Sigatoka (Mycosphaerella sp.)
Scientia Horticulturae, 56 ( 1993 ) 107-117 Elsevier Science Publishers B.V., Amsterdam
107
Effect of banana spray oil on banana yield in the absence of Sigatoka (Mycosphaerella sp. ) Y. Israeli *'a, E. Shabi b, W.R. Slabaughc aJordan Valley Banana Research Station, Zemach 15132, Israel bDepartment of Plant Pathology, ARO-Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel cISK Biotech Corporation, 11098 W. Highmont Drive, Boise, ID 83709, USA (Accepted 23 April 1993)
Abstract
A possible phytotoxic effect of banana spray oil (BSO) was studied on banana cultivar 'Grand Nain' (Musa spp., AAA subgroup ) in Israel where no yellow or black Sigatoka was present. Texaco Spraytex® CT774, at rates of 2.6, 5.2 and 7.8 1 h a - 1, was applied using simulated aerial application during two consecutive production cycles. Twelve and ten spray cycles were applied during the first and second production cycles, respectively. BSO treatments were compared with the chlorothalonil treatment (BRAVO ® 720, 2 1 ha- t ) and an untreated control. No visual phytotoxicity or very subtle symptoms resulted from BSO application even at the highest rate. However, the highest rate of BSO reduced growth rate, delayed flowering by 4 days, and reduced bunch weight by 5.6% (P< 0.05 ) during the first production cycle when compared with the untreated control. A decrease of 8.4% in bunch weight (P< 0.05 ) was observed in the second production cycle when the highest BSO rate was compared with the untreated control. Bunch weight losses were directly related to BSO application rates. The number of green leaves at harvest and number of hands per bunch were also significantly reduced during the second production cycle. Chlorothalonil application did not significantly affect any of the parameters measured in this test when compared with the untreated control. This study indicates BSO usage causes a reduction in banana yield. Key words: Banana leaf spot; Banana spray oil; Banana yield; Phytotoxicity; Sigatoka
Introduction Mineral spray oils have been in use since the late 1950s in spray programs to control banana leaf spot in most commercial growing areas (Stover, 1972; Stover and Simmonds, 1987). These oils were generally used alone or in combination with fungicides to control yellow Sigatoka caused by Mycosphaerella musicola Leach ( Cercospora musae Zimm). Banana spray oil was combined with fixed coppers or dithiocarbamates in areas with climates more favorable to disease development (Calpouzos, 1968, pp. 367-393; Stover and Simmonds, 1987). *Corresponding author.
© 1993 Elsevier Science Publishers B.V. All rights reserved 0304-4238/93/$06.00
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Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
The emergence of black Sigatoka, caused by Mycosphaerella fijiensis Morelet, led to the use of mineral spray oil to obtain good disease control with most sterol demethylation inhibitors (DMIs), the benzimidazoles, dithiocarbamates and morpholines (Stover and Simmonds, 1987). The introduction of spray oils in the late 1950s resulted in varying levels of phytotoxicity to banana foliage which was generally unacceptable at the commercial grower level. Comprehensive studies on the phytotoxicity of banana spray oil (BSO) conducted during the early 1960s have resulted in reduced danger of phytotoxicity to bananas by defining spray oil characteristics which optimize disease control and minimize phytotoxicity expression (Calpouzos et al., 1960, 1961a,b,c; Delfel et al., 1962; Corke and Jordan, 1963; Reidhart, 1964; Calpouzos and Colberg, 1964). Spray oils were found to be acceptable if they had unsulfonated residues of 90% or more, an aromatic content of 12% or less and a 50% distillation range of 346-354°C at 760 m m Hg (Calpouzos, 1968, pp. 367-393; Stover, 1972). Oils with 50% distillation below 338°C did not control Sigatoka and those above 365 °C were significantly more phytotoxic. Spray oils penetrate foliar surfaces and collect as droplets between mesophyll cells (Brun, 1958; Laville, 1963 ). Physiological evidence of spray oil phytotoxicity is also well documented, showing that the application of spray oil to banana foliage reduced photosynthetic and transpiration rates (Reidhart, 1961; Corke and Jordan, 1963; Calpouzos, 1968, pp. 367-393). The phytotoxic effect of banana spray oil has been a controversial subject for three decades. Yield losses of up to 10% have been reported by some investigators (Pont, 1960; Price, 1960). Others reported no yield reduction resuiting from BSO usage when compared with water-copper sprays (Guyot and Cuille, 1955; Desrosiers, 1958; Tolenaar, 1960; Anonymous, 1961; Calpouzos, 1968, pp. 367-393). Most tests to determine if BSO usage in spray programs causes yield loss have been conducted with low numbers of replicates on relatively large plots (5 ha or more) in order to facilitate aerial application, and in areas where leaf spot was present. The low numbers of replicates and/or variable leaf spot control probably obscured yield differences among treatments in past experiments, even when large numbers of bunches were evaluated within each treatment. Leaf spot control is variable over large plot areas and may introduce yield variability under field conditions. We tested BSO for its effect on banana yield reduction using varied application quantities over a 2 year period. The test was conducted in an area where agronomic inputs such as fertilizer and water are closely controlled and no banana leaf spot was present to obscure yield reductions related to BSO phytotoxicity. These studies were designed to determine the effects of a series of BSO application rates on vegetative growth and yield.
Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
109
Materials and methods Location a n d culturalpractices. - The study was performed in the Jordan River
Valley of Israel, which is free from the most important banana foliage diseases including yellow and black Sigatoka. Banana growth in Israel is seasonal and typical for a subtropical climate (Ticho, 1970; Israeli and Lahav, 1986, pp. 45-73 ). Growth and flowering take place during the summer months, while fruit is harvested during the fall and winter months. Uniformly aged banana cultivar 'Grand Nain' plantlets generated through tissue culture in vitro were rooted in 1 1 pots and transplanted to the field when they reached approximately 30 cm in height on 28 July 1988. The planting design was a double row with 2.5 m between rows in each plot, 2.7 m between mats within rows and 5 m between plots. Each mat contained two plants for a total of 32 plants per replicate (2078 plants h a - l ) . Two border mats were utilized to separate replicates and control interplot spray drift. The experimental design was a completely randomized block with 11 replicates and 16 mats per replicate (eight mats per row; two rows per replicate). Plants were irrigated daily during the summer months using a conventional drip irrigation system with two drip lines per row and 0.8 m between drippers. The amount of water applied was about 3200 m m year- 1which was well above normal consumptive use in Israel (Israeli and Nameri, 1987). Fertilization practices included animal manure application prior to planting, supplemented with one additional animal waste application on an annual basis. Nitrogen, in the form of ammonium nitrate and ammonium sulfate (350 kg N h a - 1 year- ~), was also applied through the drip irrigation system. Phosphorus was applied as superphosphate at the rate of 40 kg P205 h a - ~year- ~. No potassium was applied since potassium availability in Jordan Valley soils and organic amendments is considered optimum for banana cultivation. T r e a t m e n t s a n d application techniques. - Three rates of BSO in water emulsion were compared with chlorothalonil and the untreated control (Table 1 ). The higher rates of BSO and that of chlorothalonil were in the range of commercial applications (Stover, 1972; Fullerton and Stover, 1990). The BSO used, Texaco Spraytex ® CT774 (Texaco, Dallas, TX), was a narrow range, distillated petroleum mineral oil commonly used in Sigatoka spray programs. Treatments were applied with equipment which simulated aerial application, achieved with a Micro-Max ® (Micron Corp., Houston, TX) rotary atomizer operated at 3500 rev min-1 and positioned I m above the canopy on a tractor-mounted boom. Flow rates were controlled with a manostat. A minitractor was used to apply sprays from the 5-m-wide alleys, a practice which minimized soil compaction. The spray machinery was driven through control plots which minimized differences among treatments relating to soil compac-
110
Y. Israeli et al. /Scientia Horticulturae 56 (1993.) 107-I 17
Table 1 Rates of banana spray oil (BSO), emulsifier and chlorothalonil application Treatment '
BRAVO 720 Control
Texaco Spraytex ®
Adsee ® 775
CT774 (1 ha-')
(ml ha -l)
-
-
2.6 5.2 7.8
13 26 39
BRAVO® 720 (lha -t) 2.0
BSO
2.6lha-' 5.21 ha-' 7.8 1ha- ~
'The total volume applied was 251 ha- ~using water as the diluent. 29 Aug 09 Aug 19 Jul
]- FR ]_ FL
J
t
22 05Jun Jul 07 Jun 24 May 10 May 26 Apr £3 17 Apr ¢O (J
<
V
20 Nov
]
1 6 Oct
[_
02 Nov
02 Oct 19 Sep 30 Jul 17 Jul 19 Jun
FR
J
]- FL J
O_ 09 05 Jun
22 May 04 May 03 Apr
1
30 02 Dec Dec 07 Nov 24 Oct 12 Oct
IV r o
lo
20
30
40
so
60
¢o
8'o
90
100
Degrees C or Relative Humidity (%)
Fig. 1. Meteorological data and developmental stages of plants at spray application. Sprays were applied during vegetative growth (V), flowering (FL, between floral initiation and shooting) and fruiting (FR, between shooting and harvest) during 1988, 1989, and 1990.
tion. No spray drift occurred during applications. Spray coverage was good on all exposed banana foliage. Five spray applications every 2-3 weeks were made during the initial growth period following planting in the autumn of 1988 (Fig. 1 ). Spray applications were terminated when new leaf initiation ceased and restarted when new growth occurred. Twelve and ten sprays every 2-3 weeks were applied during the 1989 and 1990 growing seasons, respectively. Plants for the following season's production were approximately 1.5-1.6 m tall when spray applications were terminated during each season except in 1990, when spray application was terminated at the end of August. Termination was earlier than anticipated because of foliar overlap between plots which reduced application effi-
Y. Israeli et al. /Scientia Horticulturae 56 (1993) 107-117
111
ciency to unacceptable levels. Second cycle production plants reached peak shooting in August 1990. C l i m a t i c c o n d i t i o n s . - Temperature and humidity data were obtained from a standard meteorological station (Israel Meteorological Service) located about 1.0 km from the test site. Data for the spray dates are presented in Fig. 1. Spray applications were made during morning hours to minimize spray droplet desiccation and interplot drift.
Vegetative growth was monitored using monthly measurements of plant height, leaf emergence rates and total number of leaves per plant during the first production cycle. In addition, pseudostem circumference at 1.0 m at shooting and total leaf number at harvest were recorded. Effects on the reproductive phase were monitored by recording shooting date every 10 days, harvest date every week, number of hands per bunch and bunch weight. Additional reproductive phase data in the form of finger length and circumference (middle finger from the outer whorl of the third basal hand) were also recorded. Harvest date was determined by fullness of the fingers. All measurements, with the exception of plant height and leaf numbers, were obtained during the second production cycle. Leaves were frequently inspected for flecking and bronzing which are typical symptoms of BSO phytotoxicity on banana foliage. Data were analyzed using the software of the Statistical Analysis Systems Institute (SAS, 1987).
Data collection. -
Results
BSO application did not significantly reduce growth rates in terms of plant height at flowering and pseudostem growth rates. However, leaf initiation rates were significantly reduced at the high rate of BSO application (Table 2 ). Differences were significant among treatments in terms of total leaf numbers at flowering when comparing the highest BSO rate and the untreated control (Table 3 ). However, a significant decrease in the number of green leaves at harvest was observed in the high-rate BSO plots (4.7%) during the second production cycle (Table 3 ). A delay in flowering date was observed during the first production cycle and was related to the rate of BSO applied (Table 4). The highest rate of BSO application delayed the mean flowering date by 4 days and the mean harvesting date by 16 days during the first production cycle with no difference being detected between mean and median dates for these parameters (Table 4). Although no significant differences within these parameters were observed during the second production cycle, trends were similar to those noted above with regard to flowering and harvest date. The most obvious effect of BSO usage was the reduction in bunch weight
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Y. Israeli et al. /Scientia Horticulturae 56 (1993) 107-I 17
Table 2
The effect of banana spray oil (BSO) and chlorothalonil on growth and leaf initiation rate Treatment
Pseudostem
No. of leaves
heightl
produced1
Plant height at flowering2 (cm)
(cm)
Chlorothalonil Control
1989
1990
129" 128 ab
20.1" 20.2"
253" 253"
270 a 270"
127 "b 125 b 122 b
20.2" 20.1" 19.9 b
249 ~ 251 ~ 251"
264" 269 ~ 266"
BSO
2.61 ha -1 5.21 ha -~ 7.8 1 h a - ~
~Data reflect growth measurements from 13 October 1988 through 1 July 1989. 21989, first production cycle; 1990, second production cycle. Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05). Table 3
The effect of banana spray oil (BSO) and chlorothalonil on the number of green leaves per plant at flowering and harvest Treatment
Mean number of green leaves At flowering
Chlorothalonil Control
At harvest
1989
1990
1989
1990
11.2 ~b 11.1 ab
10.6 a 10.6 a
7,6" 7.3 ab
8.7" 8.6 "b
11.6 a 11.3 ab 11.0 b
10.5" 10.5" 10.6"
7.3 "b 7.0 b 7.2 b
8.3 be 8.3 be 8.2 ¢
BSO
2.61 ha -~ 5.21 ha-~ 7.81 ha -1
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle.
(Table 5 ). The highest BSO rate significantly reduced bunch weight during the entire 2 year test period. The bunch weight reduction was 5.6% and 8.4% during the first and second production cycles, respectively. The reduction in bunch weight appeared to be correlated with BSO application rate. Finger length was slightly reduced by BSO application during the second production cycle (Table 6 ). Finger circumference (equivalent to grade) was not affected by BSO application. The number of hands per bunch was significantly lower (3.8%) during the second production cycle in plots treated with the highest rate of BSO (Table 6). Plots receiving chlorothalonil sprays were not significantly different from untreated plots in any of the growth or production parameters measured during this experiment. No visual symptoms of phytotoxicity were evident in any of the treatments, with the exception of
Y. Israeli et aL / Scientia Horticulturae 56 (1993) 107-117
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Table 4 The effect of banana spray oil (BSO) and chlorothalonil on flowering date, harvest date and interval from flowering to harvst Treatment
Chlorothalonil Control
Mean flowering date
Mean harvest date
Mean flowering to harvest interval (days)
1989
1990
1989
1990
1989
1990
1 Aug. b 1 Aug. b
5 Aug." 5 Aug."
30 Nov. b 26 Nov. b
14 Dec." 14 Dec. a
i 19b 117 b
130" 130 a
31 Jul. b 2 Aug. "b 5 Aug."
5 Aug." 7 Aug. a 8 Aug."
26 Nov. b 1 Dec. b 12 Dec."
16 Dec. ~ 22 Dec." 25 Dec."
118 b 121 b 129"
130" 134 a 136"
BSO
2.61 ha -1 5.2 1 h a - l 7.8 1 h a - '
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle. Table 5 The effect of banana spray oil (BSO) and chlorothalonil on banana yield" Mean bunch weight (kg)
Treatment
Chlorothalonil Control
1989
1990
23.8" 23.4 "b
25.4" 25. l"b
22.7 be 22.7 bc 22.1 c
24.2 bc 23.8 Cd 23.0 d
BSO
2.6 1 ha -~ 5.21 h a - ' 7.81 ha - t
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle. Table 6 The effect of banana spray oil (BSO) and chlorothalonil on finger length, finger circumference and number of hands per bunch Treatment
Chlorothalonil Control
Mean finger length (cm)
Mean finger circumference (cm)
Mean no. of hands per bunch
1989
1990
1989
1990
1989
1990
22.0" 22.1"
21.4" 21.3 ab
11.8" i 1.8"
11.4" 11.3"
9.3" 9.1 ab
10.8" 10.6 "b
21.8" 21.9" 21.7"
21. i "~ 20.9 ¢ 21.0 be
11.8" 11.7" 11.7 a
11.3" 11.4" 11.3"
9.0 b 9.0 b 9.1 ~b
10.4 bc 10.4 ~ 10.2 c
BSO
2.61 ha -1 5.21ha -~ 7.81 ha -1
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle.
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Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
some occasional, mild leaf flecking occurring on the foliage treated with the highest rate of BSO. Discussion
Substantial bunch weight losses were observed in BSO-treated plots during both the 1989 and 1990 production cycles. These bunch weight losses were 5.6% and 8.4% in plots treated with the highest BSO rate in the first and second production cycles, respectively. Yield losses of up to 10% were reported from early BSO application experiments on banana cultivars such as 'Gros Michel', 'Lacatan' and Cavendish varieties (Pont, 1960; Price, 1960; Tolenaar, 1960). However, these yield losses were attributed primarily to the use of less refined oils. In contrast, more recent experiments with highly refined BSO applied on Cavendish varieties have not shown yield losses when applied at commercially used rates and have been regarded, in general, as safe when properly utilized in Sigatoka control programs (Fullerton and Stover, 1990). Data from this experiment clearly demonstrated that yield losses occurred when highly refined BSO was applied to the banana cultivar 'Grand Nain', a popular, short-statured Cavendish variety. Possible explanations for differences between recent BSO-yield experiments and this test are complex. Most recent experiments have utilized aircraft equipped with rotary atomizers and have been conducted in areas where Sigatoka was present. In contrast to the simulated aerial application used in this experiment, tests utilizing aircraft required comparatively large areas. Since test areas under most commercial conditions are limited by size and cost, replication number and treatment randomization probably have been suboptimal, which may account for the lack of statistical differences observed among treatments in those tests. Banana bunch weights are inherently highly variable under most commercial growing conditions, a fact which undoubtedly contributes to the inability to detect yield differences among treatments. The uniformly growing plants used in this test, derived from tissue culture in vitro, probably reduced the inherent variability normally associated with banana plant growth and yield. In addition, within commercial banana plantations, levels of black Sigatoka and other foliage diseases are usually variable, even within relatively small areas. This intrinsic variability, confounded by the effects of treatments in controlling such foliage diseases, can undoubtedly preclude statistical separation of treatment regimes. This experiment was conducted in Israel where no black or yellow Sigatoka is present, thus eliminating these diseases as factors in detecting yield losses associated with BSO use.
Plant stress caused by high temperature and inadequate moisture are known to increase BSO phytotoxicity in banana foliage which is expressed as bronz-
Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
115
ing and/or flecking (Stover, 1972). No phytotoxicity symptoms were observed in any BSO treatments in this study, except under the highest BSO regime where some flecking was observed. Ample irrigation water (3200 mm ha- 1year- 1) was applied to all test plots, thus alleviating possible plant stress conditions which can develop under Israeli cultivation and climate. Finger length was slightly reduced, whereas the number of hands per bunch (hand class) was significantly reduced by BSO treatment. Hand class reductions and finger length reduction trends probably accounted for a major portion of the bunch weight reductions observed in this test. Since a major impact on bunch weight loss can be attributed to hand class reduction, plant growth regulators may prove useful in improving hand class on plants subjected to BSO sprays. BSO usage also affected vegetative parameters as expected. Pseudostem growth rates and the number of functional leaves at harvest were significantly reduced by BSO application. A reduction in functional foliar area at harvest was reported from previous experiments (Stover, 1972). Flowering and harvest dates were delayed by 4 days and 16 days, respectively, during the first production cycle. This is the first report on flowering and harvest delay caused by BSO usage. It has been shown that a short delay in flowering of banana plants results in an even longer delay in harvest in the subtropics (Israeli and Lahav, 1986). Generally, the delay in flowering can be ascribed to reduced leaf initiation rate or increased leaf production. Leaf initiation rates were affected by BSO usage, which suggests a prolonged depression of physiological activity in BSO-treated plants. This prolonged depression of physiological activity suggested by the leaf initiation rate results suggests conformity to some of the mechanisms of BSO phytotoxicity proposed to occur in banana foliage by earlier reports (Pont, 1960; Reidhart, 1961 ). The proposed mechanisms included leaf longevity, photosynthesis and cellular necrosis. Most of the yield losses associated with BSO usage and leaf initiation rates in this test can probably be ascribed to leaf longevity and photosynthesis in the form of reduced carbon dioxide assimilation and/or assimilate transport. The effect of cellular necrosis on yield reduction in this experiment was minimal or non-existent since few visual symptoms were observed. Conclusions
The data demonstrate that BSO usage in Sigatoka control programs reduces yield. Yield reduction in this study was not correlated with visual phytotoxicity symptom expression in the field which makes it difficult to assess adverse effects from BSO usage and make appropriate spray treatment adjustments to reduce yield loss. In addition to bunch weight reduction, flowering and harvest dates were delayed during the first production cycle by BSO treatment. This suggests that continuous cumulative increases in yield loss may
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Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
occur under tropical conditions where harvesting is continuous throughout the year. Acknowledgments
The technical support of Asaf Arazi (field observations), Nimrod Nameri (statistical analysis) and Solomon Elisha (treatment application) is sincerely appreciated. References Anonymous, 1961. La premiere reunion internationale sur la production de la banane. Fruits, 16:231-242. Brun, J., 1958. Etude sur Faction des fongicides huileux dans la lutte contra la cercosporiose. Fruits 13: 3-14. Calpouzos, L., 1968. Oils. In: D.C. Torgason (Editor), Fungicides: An Advanced Treatise, Vol. 2. Academic Press, New York, pp. 367-393. Calpouzos, L. and Colberg, C., 1964. Importance of source of spray oils for Sigatoka disease control and ph2ctotoxicity to banana leaves. Phytopathology, 54: 235-236. Calpouzos, L., Brun, W.A., Theis, T. and Colberg, C., 1960. A precision spray technique for evaluating oils for Sigatoka disease control on individual banana leaves in the field. Phytopathology, 50:69-72. Calpouzos, L., Colberg, C., Theis, T. and Delfel, N.E., 1961a. Deposit rate and spray oil composition in relation to phytotoxicity and Sigatoka disease control on banana leaves. Phytopathology, 51: 582-584. Calpouzos, L., Delfel, N.E., Colberg, C. and Theis, T., 196 lb. Relation of petroleum oil composition to phytotoxicity and Sigatoka disease control on banana leaves. Phytopathology, 51: 317-321. Calpouzos, L., Delfel, N.E., Colberg, C. and Theis, T., 196 lc. Viscosity of naphthenic and paraffinic spray oils in relation to phytotoxicity and Sigatoka diseases control on banana leaves. Phytopathology, 51: 528- 531. Corke, A.T.K. and Jordan, V.W.L., 1963. Experiments on the effects ofoil treatment on banana leaves. Annual Report, Agriculture and Horticulture Research Station, University of Bristol, UK, pp. 115-123. Delfel, N.E., Calpouzos, L. and Colberg, C., 1962. Measurement of spray-oil volatility and its relation to Sigatoka fungus disease control and phytotoxicity on banana leaves. Phytopathology, 52: 913-917. Desrosiers, R., 1958. The control of Sigatoka disease on the 'Gros Michel' banana by low volume spraying in Ecuador. Min. Fomento Produccion, Direc. Gen. Agr. Quito, Ecuador Tech. Bull. 1, pp. 1-58. Fullerton, R.A. and Stover, R.H. (Editors), 1990. Sigatoka Leaf Spot Diseases of Banana. Proc. Int. Workshop, San Jose, Costa Rica, 28 March-1 April 1989, INIBAP, Montpellier, France, 374 pp. Guyot, H. and Cuille, L, 1955. Los traitements fongicides des bananeraies. II. Efficaciles des differents modes dc traitements. Role de l'huile. Fruits, 10: 101-107. Israeli, Y. and Lahav, E., 1986. Banana. In: S.P. Monselise (Editor), CRC Handbook of Fruit Set and Development. CRC Press, Boca Raton, FL, pp. 45-73. Israeli, Y. and Nameri, N., 1987. Seasonal changes in banana plant water use. Water Irrig. Rev. Isr., January 1987: 10-14.
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Laville, E., 1963. Contribution a l'etude de la penetration et la localisation des huiles dans la feuille de bananier. Fruits, 18: 339-344. Pont, W., 1960. Epidemiology and control of banana leaf spot ( M y c o s p h a e r e l l a m u s i c o l a Leach) in North Queensland. Qld. J. Agric. Sci., 17:211-272. Price, D., 1960. The effects of several spray regimes on banana fruit weights. Trop. Agric., 37: 325-328. Reidhart, J.M., 1961. Influence of petroleum oil on photosynthesis of banana leaves. Trop. Agric., 38: 23-27. Reidhart, J.M., 1964. Influence of petroleum oil fractions on Sigatoka disease control in bananas. Trop. Agric., 41:155-158. Statistical Analysis Systems Institute, 1987. SAS/STAT Guide for Personal Computers, Version 6 edn. SAS, Cary, NC, 1020 pp. Stover, R.H., 1972. Banana, Plantain, and Abaca Diseases. Commonwealth Mycological Institute, Kew, UK, 316 pp. Stover, R.H. and Simmonds, N.W., 1987. Bananas. John Wiley, New York, 468 pp. Ticho, R.T., 1970. The banana industry in Israel. Trop. Sci., 13: 289-301. Tolenaar, D., 1960. Effects of copper and oil in the control of Sigatoka banana leaf spot. Neth. J. Agric. Sci., 8: 253-260.
107
Effect of banana spray oil on banana yield in the absence of Sigatoka (Mycosphaerella sp. ) Y. Israeli *'a, E. Shabi b, W.R. Slabaughc aJordan Valley Banana Research Station, Zemach 15132, Israel bDepartment of Plant Pathology, ARO-Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel cISK Biotech Corporation, 11098 W. Highmont Drive, Boise, ID 83709, USA (Accepted 23 April 1993)
Abstract
A possible phytotoxic effect of banana spray oil (BSO) was studied on banana cultivar 'Grand Nain' (Musa spp., AAA subgroup ) in Israel where no yellow or black Sigatoka was present. Texaco Spraytex® CT774, at rates of 2.6, 5.2 and 7.8 1 h a - 1, was applied using simulated aerial application during two consecutive production cycles. Twelve and ten spray cycles were applied during the first and second production cycles, respectively. BSO treatments were compared with the chlorothalonil treatment (BRAVO ® 720, 2 1 ha- t ) and an untreated control. No visual phytotoxicity or very subtle symptoms resulted from BSO application even at the highest rate. However, the highest rate of BSO reduced growth rate, delayed flowering by 4 days, and reduced bunch weight by 5.6% (P< 0.05 ) during the first production cycle when compared with the untreated control. A decrease of 8.4% in bunch weight (P< 0.05 ) was observed in the second production cycle when the highest BSO rate was compared with the untreated control. Bunch weight losses were directly related to BSO application rates. The number of green leaves at harvest and number of hands per bunch were also significantly reduced during the second production cycle. Chlorothalonil application did not significantly affect any of the parameters measured in this test when compared with the untreated control. This study indicates BSO usage causes a reduction in banana yield. Key words: Banana leaf spot; Banana spray oil; Banana yield; Phytotoxicity; Sigatoka
Introduction Mineral spray oils have been in use since the late 1950s in spray programs to control banana leaf spot in most commercial growing areas (Stover, 1972; Stover and Simmonds, 1987). These oils were generally used alone or in combination with fungicides to control yellow Sigatoka caused by Mycosphaerella musicola Leach ( Cercospora musae Zimm). Banana spray oil was combined with fixed coppers or dithiocarbamates in areas with climates more favorable to disease development (Calpouzos, 1968, pp. 367-393; Stover and Simmonds, 1987). *Corresponding author.
© 1993 Elsevier Science Publishers B.V. All rights reserved 0304-4238/93/$06.00
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Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
The emergence of black Sigatoka, caused by Mycosphaerella fijiensis Morelet, led to the use of mineral spray oil to obtain good disease control with most sterol demethylation inhibitors (DMIs), the benzimidazoles, dithiocarbamates and morpholines (Stover and Simmonds, 1987). The introduction of spray oils in the late 1950s resulted in varying levels of phytotoxicity to banana foliage which was generally unacceptable at the commercial grower level. Comprehensive studies on the phytotoxicity of banana spray oil (BSO) conducted during the early 1960s have resulted in reduced danger of phytotoxicity to bananas by defining spray oil characteristics which optimize disease control and minimize phytotoxicity expression (Calpouzos et al., 1960, 1961a,b,c; Delfel et al., 1962; Corke and Jordan, 1963; Reidhart, 1964; Calpouzos and Colberg, 1964). Spray oils were found to be acceptable if they had unsulfonated residues of 90% or more, an aromatic content of 12% or less and a 50% distillation range of 346-354°C at 760 m m Hg (Calpouzos, 1968, pp. 367-393; Stover, 1972). Oils with 50% distillation below 338°C did not control Sigatoka and those above 365 °C were significantly more phytotoxic. Spray oils penetrate foliar surfaces and collect as droplets between mesophyll cells (Brun, 1958; Laville, 1963 ). Physiological evidence of spray oil phytotoxicity is also well documented, showing that the application of spray oil to banana foliage reduced photosynthetic and transpiration rates (Reidhart, 1961; Corke and Jordan, 1963; Calpouzos, 1968, pp. 367-393). The phytotoxic effect of banana spray oil has been a controversial subject for three decades. Yield losses of up to 10% have been reported by some investigators (Pont, 1960; Price, 1960). Others reported no yield reduction resuiting from BSO usage when compared with water-copper sprays (Guyot and Cuille, 1955; Desrosiers, 1958; Tolenaar, 1960; Anonymous, 1961; Calpouzos, 1968, pp. 367-393). Most tests to determine if BSO usage in spray programs causes yield loss have been conducted with low numbers of replicates on relatively large plots (5 ha or more) in order to facilitate aerial application, and in areas where leaf spot was present. The low numbers of replicates and/or variable leaf spot control probably obscured yield differences among treatments in past experiments, even when large numbers of bunches were evaluated within each treatment. Leaf spot control is variable over large plot areas and may introduce yield variability under field conditions. We tested BSO for its effect on banana yield reduction using varied application quantities over a 2 year period. The test was conducted in an area where agronomic inputs such as fertilizer and water are closely controlled and no banana leaf spot was present to obscure yield reductions related to BSO phytotoxicity. These studies were designed to determine the effects of a series of BSO application rates on vegetative growth and yield.
Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
109
Materials and methods Location a n d culturalpractices. - The study was performed in the Jordan River
Valley of Israel, which is free from the most important banana foliage diseases including yellow and black Sigatoka. Banana growth in Israel is seasonal and typical for a subtropical climate (Ticho, 1970; Israeli and Lahav, 1986, pp. 45-73 ). Growth and flowering take place during the summer months, while fruit is harvested during the fall and winter months. Uniformly aged banana cultivar 'Grand Nain' plantlets generated through tissue culture in vitro were rooted in 1 1 pots and transplanted to the field when they reached approximately 30 cm in height on 28 July 1988. The planting design was a double row with 2.5 m between rows in each plot, 2.7 m between mats within rows and 5 m between plots. Each mat contained two plants for a total of 32 plants per replicate (2078 plants h a - l ) . Two border mats were utilized to separate replicates and control interplot spray drift. The experimental design was a completely randomized block with 11 replicates and 16 mats per replicate (eight mats per row; two rows per replicate). Plants were irrigated daily during the summer months using a conventional drip irrigation system with two drip lines per row and 0.8 m between drippers. The amount of water applied was about 3200 m m year- 1which was well above normal consumptive use in Israel (Israeli and Nameri, 1987). Fertilization practices included animal manure application prior to planting, supplemented with one additional animal waste application on an annual basis. Nitrogen, in the form of ammonium nitrate and ammonium sulfate (350 kg N h a - 1 year- ~), was also applied through the drip irrigation system. Phosphorus was applied as superphosphate at the rate of 40 kg P205 h a - ~year- ~. No potassium was applied since potassium availability in Jordan Valley soils and organic amendments is considered optimum for banana cultivation. T r e a t m e n t s a n d application techniques. - Three rates of BSO in water emulsion were compared with chlorothalonil and the untreated control (Table 1 ). The higher rates of BSO and that of chlorothalonil were in the range of commercial applications (Stover, 1972; Fullerton and Stover, 1990). The BSO used, Texaco Spraytex ® CT774 (Texaco, Dallas, TX), was a narrow range, distillated petroleum mineral oil commonly used in Sigatoka spray programs. Treatments were applied with equipment which simulated aerial application, achieved with a Micro-Max ® (Micron Corp., Houston, TX) rotary atomizer operated at 3500 rev min-1 and positioned I m above the canopy on a tractor-mounted boom. Flow rates were controlled with a manostat. A minitractor was used to apply sprays from the 5-m-wide alleys, a practice which minimized soil compaction. The spray machinery was driven through control plots which minimized differences among treatments relating to soil compac-
110
Y. Israeli et al. /Scientia Horticulturae 56 (1993.) 107-I 17
Table 1 Rates of banana spray oil (BSO), emulsifier and chlorothalonil application Treatment '
BRAVO 720 Control
Texaco Spraytex ®
Adsee ® 775
CT774 (1 ha-')
(ml ha -l)
-
-
2.6 5.2 7.8
13 26 39
BRAVO® 720 (lha -t) 2.0
BSO
2.6lha-' 5.21 ha-' 7.8 1ha- ~
'The total volume applied was 251 ha- ~using water as the diluent. 29 Aug 09 Aug 19 Jul
]- FR ]_ FL
J
t
22 05Jun Jul 07 Jun 24 May 10 May 26 Apr £3 17 Apr ¢O (J
<
V
20 Nov
]
1 6 Oct
[_
02 Nov
02 Oct 19 Sep 30 Jul 17 Jul 19 Jun
FR
J
]- FL J
O_ 09 05 Jun
22 May 04 May 03 Apr
1
30 02 Dec Dec 07 Nov 24 Oct 12 Oct
IV r o
lo
20
30
40
so
60
¢o
8'o
90
100
Degrees C or Relative Humidity (%)
Fig. 1. Meteorological data and developmental stages of plants at spray application. Sprays were applied during vegetative growth (V), flowering (FL, between floral initiation and shooting) and fruiting (FR, between shooting and harvest) during 1988, 1989, and 1990.
tion. No spray drift occurred during applications. Spray coverage was good on all exposed banana foliage. Five spray applications every 2-3 weeks were made during the initial growth period following planting in the autumn of 1988 (Fig. 1 ). Spray applications were terminated when new leaf initiation ceased and restarted when new growth occurred. Twelve and ten sprays every 2-3 weeks were applied during the 1989 and 1990 growing seasons, respectively. Plants for the following season's production were approximately 1.5-1.6 m tall when spray applications were terminated during each season except in 1990, when spray application was terminated at the end of August. Termination was earlier than anticipated because of foliar overlap between plots which reduced application effi-
Y. Israeli et al. /Scientia Horticulturae 56 (1993) 107-117
111
ciency to unacceptable levels. Second cycle production plants reached peak shooting in August 1990. C l i m a t i c c o n d i t i o n s . - Temperature and humidity data were obtained from a standard meteorological station (Israel Meteorological Service) located about 1.0 km from the test site. Data for the spray dates are presented in Fig. 1. Spray applications were made during morning hours to minimize spray droplet desiccation and interplot drift.
Vegetative growth was monitored using monthly measurements of plant height, leaf emergence rates and total number of leaves per plant during the first production cycle. In addition, pseudostem circumference at 1.0 m at shooting and total leaf number at harvest were recorded. Effects on the reproductive phase were monitored by recording shooting date every 10 days, harvest date every week, number of hands per bunch and bunch weight. Additional reproductive phase data in the form of finger length and circumference (middle finger from the outer whorl of the third basal hand) were also recorded. Harvest date was determined by fullness of the fingers. All measurements, with the exception of plant height and leaf numbers, were obtained during the second production cycle. Leaves were frequently inspected for flecking and bronzing which are typical symptoms of BSO phytotoxicity on banana foliage. Data were analyzed using the software of the Statistical Analysis Systems Institute (SAS, 1987).
Data collection. -
Results
BSO application did not significantly reduce growth rates in terms of plant height at flowering and pseudostem growth rates. However, leaf initiation rates were significantly reduced at the high rate of BSO application (Table 2 ). Differences were significant among treatments in terms of total leaf numbers at flowering when comparing the highest BSO rate and the untreated control (Table 3 ). However, a significant decrease in the number of green leaves at harvest was observed in the high-rate BSO plots (4.7%) during the second production cycle (Table 3 ). A delay in flowering date was observed during the first production cycle and was related to the rate of BSO applied (Table 4). The highest rate of BSO application delayed the mean flowering date by 4 days and the mean harvesting date by 16 days during the first production cycle with no difference being detected between mean and median dates for these parameters (Table 4). Although no significant differences within these parameters were observed during the second production cycle, trends were similar to those noted above with regard to flowering and harvest date. The most obvious effect of BSO usage was the reduction in bunch weight
1 12
Y. Israeli et al. /Scientia Horticulturae 56 (1993) 107-I 17
Table 2
The effect of banana spray oil (BSO) and chlorothalonil on growth and leaf initiation rate Treatment
Pseudostem
No. of leaves
heightl
produced1
Plant height at flowering2 (cm)
(cm)
Chlorothalonil Control
1989
1990
129" 128 ab
20.1" 20.2"
253" 253"
270 a 270"
127 "b 125 b 122 b
20.2" 20.1" 19.9 b
249 ~ 251 ~ 251"
264" 269 ~ 266"
BSO
2.61 ha -1 5.21 ha -~ 7.8 1 h a - ~
~Data reflect growth measurements from 13 October 1988 through 1 July 1989. 21989, first production cycle; 1990, second production cycle. Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05). Table 3
The effect of banana spray oil (BSO) and chlorothalonil on the number of green leaves per plant at flowering and harvest Treatment
Mean number of green leaves At flowering
Chlorothalonil Control
At harvest
1989
1990
1989
1990
11.2 ~b 11.1 ab
10.6 a 10.6 a
7,6" 7.3 ab
8.7" 8.6 "b
11.6 a 11.3 ab 11.0 b
10.5" 10.5" 10.6"
7.3 "b 7.0 b 7.2 b
8.3 be 8.3 be 8.2 ¢
BSO
2.61 ha -~ 5.21 ha-~ 7.81 ha -1
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle.
(Table 5 ). The highest BSO rate significantly reduced bunch weight during the entire 2 year test period. The bunch weight reduction was 5.6% and 8.4% during the first and second production cycles, respectively. The reduction in bunch weight appeared to be correlated with BSO application rate. Finger length was slightly reduced by BSO application during the second production cycle (Table 6 ). Finger circumference (equivalent to grade) was not affected by BSO application. The number of hands per bunch was significantly lower (3.8%) during the second production cycle in plots treated with the highest rate of BSO (Table 6). Plots receiving chlorothalonil sprays were not significantly different from untreated plots in any of the growth or production parameters measured during this experiment. No visual symptoms of phytotoxicity were evident in any of the treatments, with the exception of
Y. Israeli et aL / Scientia Horticulturae 56 (1993) 107-117
I 13
Table 4 The effect of banana spray oil (BSO) and chlorothalonil on flowering date, harvest date and interval from flowering to harvst Treatment
Chlorothalonil Control
Mean flowering date
Mean harvest date
Mean flowering to harvest interval (days)
1989
1990
1989
1990
1989
1990
1 Aug. b 1 Aug. b
5 Aug." 5 Aug."
30 Nov. b 26 Nov. b
14 Dec." 14 Dec. a
i 19b 117 b
130" 130 a
31 Jul. b 2 Aug. "b 5 Aug."
5 Aug." 7 Aug. a 8 Aug."
26 Nov. b 1 Dec. b 12 Dec."
16 Dec. ~ 22 Dec." 25 Dec."
118 b 121 b 129"
130" 134 a 136"
BSO
2.61 ha -1 5.2 1 h a - l 7.8 1 h a - '
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle. Table 5 The effect of banana spray oil (BSO) and chlorothalonil on banana yield" Mean bunch weight (kg)
Treatment
Chlorothalonil Control
1989
1990
23.8" 23.4 "b
25.4" 25. l"b
22.7 be 22.7 bc 22.1 c
24.2 bc 23.8 Cd 23.0 d
BSO
2.6 1 ha -~ 5.21 h a - ' 7.81 ha - t
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle. Table 6 The effect of banana spray oil (BSO) and chlorothalonil on finger length, finger circumference and number of hands per bunch Treatment
Chlorothalonil Control
Mean finger length (cm)
Mean finger circumference (cm)
Mean no. of hands per bunch
1989
1990
1989
1990
1989
1990
22.0" 22.1"
21.4" 21.3 ab
11.8" i 1.8"
11.4" 11.3"
9.3" 9.1 ab
10.8" 10.6 "b
21.8" 21.9" 21.7"
21. i "~ 20.9 ¢ 21.0 be
11.8" 11.7" 11.7 a
11.3" 11.4" 11.3"
9.0 b 9.0 b 9.1 ~b
10.4 bc 10.4 ~ 10.2 c
BSO
2.61 ha -1 5.21ha -~ 7.81 ha -1
Values in each column followed by the same superscript do not differ significantly using Duncan's multiple range test ( P < 0.05 ); 1989, first production cycle; 1990, second production cycle.
1 14
Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
some occasional, mild leaf flecking occurring on the foliage treated with the highest rate of BSO. Discussion
Substantial bunch weight losses were observed in BSO-treated plots during both the 1989 and 1990 production cycles. These bunch weight losses were 5.6% and 8.4% in plots treated with the highest BSO rate in the first and second production cycles, respectively. Yield losses of up to 10% were reported from early BSO application experiments on banana cultivars such as 'Gros Michel', 'Lacatan' and Cavendish varieties (Pont, 1960; Price, 1960; Tolenaar, 1960). However, these yield losses were attributed primarily to the use of less refined oils. In contrast, more recent experiments with highly refined BSO applied on Cavendish varieties have not shown yield losses when applied at commercially used rates and have been regarded, in general, as safe when properly utilized in Sigatoka control programs (Fullerton and Stover, 1990). Data from this experiment clearly demonstrated that yield losses occurred when highly refined BSO was applied to the banana cultivar 'Grand Nain', a popular, short-statured Cavendish variety. Possible explanations for differences between recent BSO-yield experiments and this test are complex. Most recent experiments have utilized aircraft equipped with rotary atomizers and have been conducted in areas where Sigatoka was present. In contrast to the simulated aerial application used in this experiment, tests utilizing aircraft required comparatively large areas. Since test areas under most commercial conditions are limited by size and cost, replication number and treatment randomization probably have been suboptimal, which may account for the lack of statistical differences observed among treatments in those tests. Banana bunch weights are inherently highly variable under most commercial growing conditions, a fact which undoubtedly contributes to the inability to detect yield differences among treatments. The uniformly growing plants used in this test, derived from tissue culture in vitro, probably reduced the inherent variability normally associated with banana plant growth and yield. In addition, within commercial banana plantations, levels of black Sigatoka and other foliage diseases are usually variable, even within relatively small areas. This intrinsic variability, confounded by the effects of treatments in controlling such foliage diseases, can undoubtedly preclude statistical separation of treatment regimes. This experiment was conducted in Israel where no black or yellow Sigatoka is present, thus eliminating these diseases as factors in detecting yield losses associated with BSO use.
Plant stress caused by high temperature and inadequate moisture are known to increase BSO phytotoxicity in banana foliage which is expressed as bronz-
Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
115
ing and/or flecking (Stover, 1972). No phytotoxicity symptoms were observed in any BSO treatments in this study, except under the highest BSO regime where some flecking was observed. Ample irrigation water (3200 mm ha- 1year- 1) was applied to all test plots, thus alleviating possible plant stress conditions which can develop under Israeli cultivation and climate. Finger length was slightly reduced, whereas the number of hands per bunch (hand class) was significantly reduced by BSO treatment. Hand class reductions and finger length reduction trends probably accounted for a major portion of the bunch weight reductions observed in this test. Since a major impact on bunch weight loss can be attributed to hand class reduction, plant growth regulators may prove useful in improving hand class on plants subjected to BSO sprays. BSO usage also affected vegetative parameters as expected. Pseudostem growth rates and the number of functional leaves at harvest were significantly reduced by BSO application. A reduction in functional foliar area at harvest was reported from previous experiments (Stover, 1972). Flowering and harvest dates were delayed by 4 days and 16 days, respectively, during the first production cycle. This is the first report on flowering and harvest delay caused by BSO usage. It has been shown that a short delay in flowering of banana plants results in an even longer delay in harvest in the subtropics (Israeli and Lahav, 1986). Generally, the delay in flowering can be ascribed to reduced leaf initiation rate or increased leaf production. Leaf initiation rates were affected by BSO usage, which suggests a prolonged depression of physiological activity in BSO-treated plants. This prolonged depression of physiological activity suggested by the leaf initiation rate results suggests conformity to some of the mechanisms of BSO phytotoxicity proposed to occur in banana foliage by earlier reports (Pont, 1960; Reidhart, 1961 ). The proposed mechanisms included leaf longevity, photosynthesis and cellular necrosis. Most of the yield losses associated with BSO usage and leaf initiation rates in this test can probably be ascribed to leaf longevity and photosynthesis in the form of reduced carbon dioxide assimilation and/or assimilate transport. The effect of cellular necrosis on yield reduction in this experiment was minimal or non-existent since few visual symptoms were observed. Conclusions
The data demonstrate that BSO usage in Sigatoka control programs reduces yield. Yield reduction in this study was not correlated with visual phytotoxicity symptom expression in the field which makes it difficult to assess adverse effects from BSO usage and make appropriate spray treatment adjustments to reduce yield loss. In addition to bunch weight reduction, flowering and harvest dates were delayed during the first production cycle by BSO treatment. This suggests that continuous cumulative increases in yield loss may
1 16
Y. Israeli et al. / Scientia Horticulturae 56 (1993) 107-117
occur under tropical conditions where harvesting is continuous throughout the year. Acknowledgments
The technical support of Asaf Arazi (field observations), Nimrod Nameri (statistical analysis) and Solomon Elisha (treatment application) is sincerely appreciated. References Anonymous, 1961. La premiere reunion internationale sur la production de la banane. Fruits, 16:231-242. Brun, J., 1958. Etude sur Faction des fongicides huileux dans la lutte contra la cercosporiose. Fruits 13: 3-14. Calpouzos, L., 1968. Oils. In: D.C. Torgason (Editor), Fungicides: An Advanced Treatise, Vol. 2. Academic Press, New York, pp. 367-393. Calpouzos, L. and Colberg, C., 1964. Importance of source of spray oils for Sigatoka disease control and ph2ctotoxicity to banana leaves. Phytopathology, 54: 235-236. Calpouzos, L., Brun, W.A., Theis, T. and Colberg, C., 1960. A precision spray technique for evaluating oils for Sigatoka disease control on individual banana leaves in the field. Phytopathology, 50:69-72. Calpouzos, L., Colberg, C., Theis, T. and Delfel, N.E., 1961a. Deposit rate and spray oil composition in relation to phytotoxicity and Sigatoka disease control on banana leaves. Phytopathology, 51: 582-584. Calpouzos, L., Delfel, N.E., Colberg, C. and Theis, T., 196 lb. Relation of petroleum oil composition to phytotoxicity and Sigatoka disease control on banana leaves. Phytopathology, 51: 317-321. Calpouzos, L., Delfel, N.E., Colberg, C. and Theis, T., 196 lc. Viscosity of naphthenic and paraffinic spray oils in relation to phytotoxicity and Sigatoka diseases control on banana leaves. Phytopathology, 51: 528- 531. Corke, A.T.K. and Jordan, V.W.L., 1963. Experiments on the effects ofoil treatment on banana leaves. Annual Report, Agriculture and Horticulture Research Station, University of Bristol, UK, pp. 115-123. Delfel, N.E., Calpouzos, L. and Colberg, C., 1962. Measurement of spray-oil volatility and its relation to Sigatoka fungus disease control and phytotoxicity on banana leaves. Phytopathology, 52: 913-917. Desrosiers, R., 1958. The control of Sigatoka disease on the 'Gros Michel' banana by low volume spraying in Ecuador. Min. Fomento Produccion, Direc. Gen. Agr. Quito, Ecuador Tech. Bull. 1, pp. 1-58. Fullerton, R.A. and Stover, R.H. (Editors), 1990. Sigatoka Leaf Spot Diseases of Banana. Proc. Int. Workshop, San Jose, Costa Rica, 28 March-1 April 1989, INIBAP, Montpellier, France, 374 pp. Guyot, H. and Cuille, L, 1955. Los traitements fongicides des bananeraies. II. Efficaciles des differents modes dc traitements. Role de l'huile. Fruits, 10: 101-107. Israeli, Y. and Lahav, E., 1986. Banana. In: S.P. Monselise (Editor), CRC Handbook of Fruit Set and Development. CRC Press, Boca Raton, FL, pp. 45-73. Israeli, Y. and Nameri, N., 1987. Seasonal changes in banana plant water use. Water Irrig. Rev. Isr., January 1987: 10-14.
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Laville, E., 1963. Contribution a l'etude de la penetration et la localisation des huiles dans la feuille de bananier. Fruits, 18: 339-344. Pont, W., 1960. Epidemiology and control of banana leaf spot ( M y c o s p h a e r e l l a m u s i c o l a Leach) in North Queensland. Qld. J. Agric. Sci., 17:211-272. Price, D., 1960. The effects of several spray regimes on banana fruit weights. Trop. Agric., 37: 325-328. Reidhart, J.M., 1961. Influence of petroleum oil on photosynthesis of banana leaves. Trop. Agric., 38: 23-27. Reidhart, J.M., 1964. Influence of petroleum oil fractions on Sigatoka disease control in bananas. Trop. Agric., 41:155-158. Statistical Analysis Systems Institute, 1987. SAS/STAT Guide for Personal Computers, Version 6 edn. SAS, Cary, NC, 1020 pp. Stover, R.H., 1972. Banana, Plantain, and Abaca Diseases. Commonwealth Mycological Institute, Kew, UK, 316 pp. Stover, R.H. and Simmonds, N.W., 1987. Bananas. John Wiley, New York, 468 pp. Ticho, R.T., 1970. The banana industry in Israel. Trop. Sci., 13: 289-301. Tolenaar, D., 1960. Effects of copper and oil in the control of Sigatoka banana leaf spot. Neth. J. Agric. Sci., 8: 253-260.