Silverleaf Whitefly Control Is Critical

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Editor’s Note: During the Florida Ag Expo held at the Gulf Coast Research and Education Center in November, Dr. Dave Schuster provided a presentation on problem vegetable diseases in Florida and their control. The following is a synopsis of his presentation. Special thanks to DuPont Crop Protection for sponsoring this six-part series of extended coverage from the Florida Ag Expo.

The silverleaf whitefly (SLWF), Bemisia argentifolii, remains the key insect pest of tomatoes in south Florida, primarily as a vector of tomato yellow leaf curl virus (TYLCV). Recommendations for managing SLWF, TYLCV, and insecticide resistance include insecticidal and cultural control practices and can be found at http://edis.ifas.ufl.edu/IN695.

A program for monitoring resistance of SLWF to insecticides was continued in 2008 and included four neonicotinoid insecticides (Admire Pro, Bayer CropScience; Platinum, Syngenta Crop Protection; Assail, UPI; and Venom, Valent USA), the pyrethroid bifenthrin, the organochlorine endosulfan, and the insect growth regulator Courier (buprofezin, Nichino America). Field populations were established with nymphal infested foliage and were tested for susceptibility in lab bioassays using the doses that were estimated to cause 50% and 95% mortality of a known susceptible laboratory colony for each respective insecticide. Results indicated that there is apparent tolerance in SLWF adults to all of the neonicotinoids and to the pyrethroid at the lower dose and to the neonicotinoids, imidacloprid (Admire Pro and others), and Platinum at the higher dose. However, all of the neonicotiniods still provide comparable residual control of nymphs in field trials. Results further suggest adult susceptibility at the higher dose with Assail and Venom and at both doses with endosulfan (adults) and Courier (nymphs).

With the increasing SLWF tolerance suggested with some insecticides, it is fortunate that there are new products with whitefly activity. The products are in new or different chemical classes and can be rotated as part of a resistance management program. Coragen (rynaxypyr, DuPont Crop Protection) is a systemic insecticide in a new chemical class that has provided residual reduction in the number of whitefly nymphs when applied by drip application. Movento, (spirotetramat, Bayer CropScience), is in the same class as Bayer’s Oberon, but is systemic and is active at lower rates. Both have provided excellent residual control of nymphs and have resulted in delayed mortality of adults, reduced oviposition, and reduced egg hatch. Requiem (extract of chenopodium ambrosioides near ambrosioides, AgraQuest) has contact activity against nymphs and adults and has resulted in fewer plants with symptoms of TYLCV. Rimon (novaluron, Chemtura Corp.) is an insect growth regulator that has provided good residual control of nymphs.

In conclusion, there are issues of possible tolerance of SLWF adults to the neonicotinoids and the pyrethroids as residues degrade to lower doses. Adult tolerance to a higher dose was indicated with imidacloprid and Platinum. Endosulfan and Courier still appear to be effective against adults and nymphs, respectively, and there are newly registered products to aid in management of these issues.