Influence of Endosulfan Sprays and Aluminum Mulch on Sweetpotato Whitefly Disorders of Zucchini Squash and Tomatoes

Abstract

Sweetpotato whitefly (Bemisia tabaci Gennadius) (SPWF) is a major pest throughout the southern USA. It is associated with the economically important disorders tomato irregular ripening (TIR) and squash silver leaf (SSL). Two possible components of SPWF management are the insecticide endosulfan (6,7,8,10,10-hexachloro-1,5,5a,6,9,9a-hexahyde-6,9-methano-2,4,3-benzodioxathiepin 3-oxide) and aluminum reflective mulch. This study was conducted to determine the effect of these control procedures, separately or in combination, on SPWF populations, the TIR and SSL disorders, fruit quality, and fruit yield of tomatoes (Lycopersicon esculentum Mill.) and zucchini squash (Cucurbita pepo L.). These parameters were evaluated in field plots during both the spring and fall of 1990. Tomato fruit yield increased (13 000 to 39 000 lb/acre), culls decreased (45 to 7%), and the percentage of TIR fruit decreased (52 to 22%) in the spring experiment as a result of endosulfan spray applications. Endosulfan sprays had no detectable effect on tomato fruit quality or yield in the fall experiment, and aluminum reflective mulch had no effect during either season. Zucchini squash yields were not affected by aluminum reflective mulch or weekly endosulfan spray applications in either experiment. Endosulfan reduced the percentage of plants with symptoms of squash SSL from 54 to 22% in the spring experiment. No SSL occurred in the fall planting. The increase in SPWF population in the squash and tomato plots was not affected by the aluminum reflective mulch or endosulfan sprays during either season. Our data suggest that environmental or physiological factors in combination with SPWF influence the incidence of SSL on squash and TIR on tomatoes. Research Question Sweetpotato whitefly (Bemisia tabaci Gennadius) can cause damage on squash (Cucurbita pepo L.) and tomatoes (Lycopersicon esculentum Mill.) by both direct feeding and the viruses it transmits. This study compares the influence of endosulfan (6,7,8,10,10-hexachloro-1,5,5a,6,9,9a-hexahyde-6,9-methano-2,4,3-benzodioxathiepin 3-oxide) sprays and reflective aluminum mulch on whitefly populations and the whitefly-induced disorders squash silver leaf and tomato irregular ripening. Literature Summary Several insecticides, including endosulfan, are known to reduce sweetpotato whitefly populations. Various colored mulches, including aluminum, also have been shown to reduce whitefly populations. Study Description Tomatoes and zucchini squash were grown in the field in the spring and fall of 1990 in Ft. Pierce, FL. Each of the plantings was divided into plots, which were treated with a weekly spray application of endosulfan, aluminum reflective mulch, both endosulfan and aluminum mulch, or neither endosulfan nor aluminum mulch. Sweetpotato whitefly populations, the incidence of tomato irregular ripening and squash silver leaf, and tomato and squash yields were monitored throughout the growing season. Applied Question Do endosulfan sprays and/or aluminum reflective mulch influence tomato or squash yields, tomato irregular ripening or squash silver leaf, or sweetpotato whitefly populations? Tomato yields were significantly increased in plots with weekly applications of endosulfan in the spring experiment, but not the fall experiment. The percentage of tomato irregular ripening also was reduced significantly by the endosulfan spray treatments in the spring experiment. Marketable squash yields were not affected by any of the treatments. In the spring experiment, however, weekly endosulfan spray applications reduced squash silver leaf symptoms. There were no significant differences in the mean weekly adult sweetpotato whitefly populations for any of the treatments in either the spring or fall experiments. In addition, aluminum painted mulch had no effect on tomato or squash yields, fruit quality, sweetpotato whitefly induced diseases, or adult sweetpotato whitefly populations. Table 1. Influence of endosulfan sprays and aluminum reflective mulch on tomato and squash yields, tomato irregular ripening and squash silver leaf, and sweetpotato whitefly populations. Tomatoes* Squash* Spring Fall Spring Fall Treatment Yield† TIR SPWF Yield† TIR SPWF Yield† SSL SPWF Yield† SSL SPWF Endosulfan + + - - - - - - - - NA - Reflective mulch - - - - - - - - - - NA - Endosulfan plus + + - - - - - + - - NA - reflective mulch * A plus sign indicates that the yield or incidence was significantly greater (P = 0.05%) than that of the untreated control. A minus sign indicates the yield or incidence was not significantly greater. NA indicates no squash silver leaf was present in the plots. † Yield was measured in both number and weight of marketable fruit per acre.