Recommendations for resistance management
In 2005, Schuster and a group of Extension researchers and educators, manufacturers, commodity group leaders and scouts drafted guidelines to help growers manage whiteflies, whitefly-vectored viruses and insecticide resistance.
Among the recommendations were using neonicotinoids only during the first six weeks after transplanting and preferably as a soil application.
If growers needed additional adult whitefly control during that early period, they could return with a different mode of action applied as foliar treatments.
The reason was to reduce nymph exposure to neonicotinoids later in the season, Schuster says.
The recommendations also called for crop destruction within five days after the end of harvest to quickly remove host material.
In addition, they recommended a two-month host-free period, preferably between mid-June and mid-August, when adult whiteflies would not be exposed to insecticides.
Whiteflies take two to six generations to regain sensitivity to the insecticides, and each generation takes two to three weeks.
But some growers are not heeding the recommendations, Schuster says.
“The tomato-free period is very short,” he says. “So the whiteflies are coming out of the spring crop, and they’re going right back into the fall exposed. They have a reduced opportunity to revert back to susceptible.”
The host-free period also would help break the virus disease cycle, since it would reduce the number of reservoir hosts from which whiteflies could acquire the pathogens, Schuster says.
Compounding the problem are three whitefly-vectored cucurbit viruses, including watermelon vine decline, he says.
As a result, growers also are applying neonicotinoids to cucurbits, further exposing the whitefly to the products.
Contact Vicky Boyd at firstname.lastname@example.org or (209) 571-0414.
Management of Whiteflies, Whitefly-Vectored Plant Virus, and Insecticide Resistance for Vegetable Production in Southern Florida