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Methyl bromide phase out web site. http://www.epa.gov.sp- Lumsden, R. D., J. A. Lewis, and G. C. Papavizas. 1983. Effect of organic dpublc/mbr/. amendments on soilborne plant diseases and pathogen antagonists. p. 51- Watkins, G.M. 1961. Physiology of Sclerotium rolfsii with emphasis on parasit- 70. In W. Loceretz (ed). Environmentally Sound Agriculture. Praeger, ism. Phytopathology 51:110-113. New York. World Meteorological Organization. 1998. Scientific Assessment of Ozone Maynard, D. N. and S. M. Olson. 2001. Vegetable production guide for Flor- Depletion: 1998. Executive Summary. Global Ozone Research and Moni- ida. University of Florida Extension, Citrus & Vegetable Magazine. toring Project – Report No. 44. Proc. Fla. State Hort. Soc. 115:321-329. 2002. COMPARISON OF IMIDACLOPRID AND THIAMETHOXAM FOR CONTROL OF THE SILVERLEAF WHITEFLY, BEMISIA ARGENTIFOLII, AND THE LEAFMINER, LIRIOMYZA TRIFOLII, ON TOMATO DAVID J. SCHUSTER spring of 2002 to compare the efficacy of imidacloprid and thi- University of Florida, IFAS amethoxam. When imidacloprid 2F (16 oz/acre) or thiamethox- Gulf Coast Research and Education Center am 2SC (8 oz/acre) were applied to the soil at or within 3 weeks Bradenton, FL 34203 of transplanting, both provided control of whitefly nymphs for eight to 12 weeks at nine sites on sandy soil but only 3 to 5 weeks at one site on gravelly loam soil. Control with imidaclo- ROBERT F. MORRIS II prid appeared to be slightly greater and to persist slightly long- Bayer CropScience er at three sites, although differences were not significant Lakeland, FL 33811 when the 2002 data were averaged over all experiments. Foliar applications of imidacloprid 1.6F at 3.75 oz/acre and thia- Additional index words. chemical control, Lycopersicon esculen- methoxam 25WG at 4 oz/acre at a threshold of five nymphs/10 leaflets also provided significant control of nymphs, although tum, insecticidal control, imidacloprid, thiamethoxam control was not as good as with soil applications, and control appeared to be greater with thiamethoxam. The incidences of Abstract. The silverleaf whitefly, Bemisia argentifolii Bellows & plants with symptoms of TYLCV were reduced with soil appli- Perring, also known as strain B of the sweetpotato whitefly [B. cations but not foliar applications. Imidacloprid appeared to tabaci (Genn.)], is the dominant pest of tomatoes, Lycopersi- provide greater and more consistent reductions in the occur- con esculentum Mill, in southern Florida. The insect causes rence of TYLCV infected plants at three sites as well as when damage directly by inducing an irregular ripening disorder of the data were averaged over six sites in 2002, although differ- tomato and indirectly by transmitting plant viruses, particular- ences from thiamethoxam were small and not significant. Soil ly tomato yellow leaf curl virus (TYLCV). The leafminer, Liri- applications of either insecticide resulted in significant reduc- omyza trifolii (Burgess), has long been considered a serious tions of L. trifolii leafmines, although control was consistently pest of tomatoes in Florida, causing defoliation through min- better with thiamethoxam. ing of leaves by larvae. Imidacloprid and thiamethoxam are members of a new class of systemic, nicotinoid insecticides that can be applied either as soil drenches or as foliar sprays. The silverleaf whitefly, Bemisia argentifolii Bellows & Per- Two experiments were conducted in the fall seasons of 2000 ring, also know as the B strain of the sweetpotato whitefly [B. and 2001 and 10 experiments were conducted during the tabaci (Gennadius)], is the dominant pest of tomatoes, Lycoper- sicon esculentum Mill, in southern Florida (Schuster et al. 1996a). The insect causes direct damage to tomato manifested This research was supported by Bayer Crop Sciences and by the Florida Agricultural Experiment Station, and approved for publication as Journal Se- as spotting of leaves, wilting and death of plants, and irregular ries No. R-08945. ripening of fruit (Schuster et al., 1996b). The insect is even Proc. Fla. State Hort. Soc. 115: 2002. 321 more damaging as a vector of plant viruses including tomato Materials and Methods mottle virus (ToMoV) and tomato yellow leaf curl virus (TYL- CV). The latter virus is particularly devastating, causing flower Experiments in 2000 and 2001. Two experiments were con- abscission and severe plant stunting (Polston et al., 1999). ducted at the Gulf Coast Research and Education Center The leafminer, Liriomyza trifolii (Burgess), has long been (GCREC), Bradenton. Transplants of the tomato cultivar considered a serious pest of tomatoes in Florida (Schuster et Agriset were set 21 Sept. 2000 and 11 Sept. 2001 18 inches al., 1996a) and recently has become more problematic apart on raised beds of EauGallie fine sand covered with (Schuster, personal observation). The larval feeding within white polyethylene mulch. Plots were three-21 ft long rows on the leaves causes serpentine mines and can result in signifi- 5-ft centers and treatments were replicated four times in ran- cant defoliation of plants, particularly when secondary micro- domized complete block designs. Soil drenches of imidaclo- organisms invade the mines (Musgrave et al., 1975). As is the prid 2F (Admire® 16 oz/acre) and thiamethoxam 2SC case with L. sativae Blanchard, the leafminer is considered a (Platinum®, 8 oz/acre) were applied at transplanting in 4 oz secondary pest; i.e., it generally is kept below economically of water per plant. In 2001 imidacloprid 1.6F (Provado®, 3.75 damaging levels by natural enemies, principally hymenopter- oz/acre) and thiamethoxam 25WG (Actara®, 4 oz/acre) ous parasites, but increases to levels requiring control when were applied foliarly when whitefly densities approached or the densities of natural enemies are reduced, principally by reached the threshold of ≥5 sessile nymphs (2nd or 3rd in- the use of broad spectrum insecticides (Oatman and stars) and/or pupae (4th instars or red eye nymphs) per 10 Kennedy, 1976). terminal leaflets of the seventh or eighth leaf from the top of Nicotinoids are a new class of neurotoxins also referred to one stem from each of the middle 10 plants in the middle row as neonicotinoids, nitroguanidines, nitromethylenes and of the respective plots (Schuster, 1998; 2002). Applications chloronicotinyls. The nicotinoids are structured after natural- were made with a self-propelled sprayer operated at 200 psi ly occurring nicotine compounds and act similarly on the cen- and 3.4 mph. It was fitted with eight Albuz orange nozzles per tral nervous system of insects, irreversibly blocking the row and delivered 60 (four nozzles open) or 120 (eight noz- postsynaptic nicotinergic acetylcholine receptors (Bai et al., zles open) gpa, depending upon plant height. In both exper- 1991). The high water solubility of the nicotinoids give them iments Bacillus thuringiensis Berliner (Mattch at 2 qt/acre, excellent systemic properties and long residual activity, which Javelin at 2 lb/acre, or XenTari at 2 lb/acre) or spinosad makes them particularly effective against sucking insects. Nic- (SpinTor at 6 oz/acre) were applied weekly to control lepi- otinoids generally have low mammalian toxicity relative to dopterous larvae, particularly the southern armyworm other neurotoxins and are relatively non-toxic to non-target [Spodoptera eridania (Cramer)]. The number of plants in each species (Wolweber and Tietjen, 1999), which makes them de- plot with definite symptoms of TYLCV were recorded weekly. sirable for integrating into pest management programs. Nic- The numbers of sessile nymphs and pupae of the silverleaf otinoids can be applied as soil drenches or as foliar sprays. whitefly were counted weekly as above. In 2001, the number Imidacloprid (Bayer Corporation, Kansas City, Mo.) and of Liriomyza leafmines was counted by each of two people, one thiamethoxam (Syngenta Crop Protection, Inc., Greensboro, on each side of the middle row of each plot, during a 2-min N.C.) are two nicotinoids that have registrations on vegetable search of each plot on 6 Dec. and the counts by the two peo- crops including tomato. The former was the first nicotinoid ple were combined for each plot.