[Editor’s Note: Interview was conducted and the article written before Hurricane Irma’s impact]
Spring 2017 could be described as epic for some Florida growers when it comes to describing whitefly infestations and troubles. The same could be said for growers dealing with the pest in Georgia during the summer.
“We have not had a light pressure whitefly year in quite some time, but this past spring was really unusual,” says Hugh Smith, an Assistant Professor of vegetable entomology with UF/IFAS. “It was a very bad spring, particularly for cucurbits and especially melons because there are three viruses transmitted by whitefly.”
Smith says tomato growers took a hit as well with tomato yellow leaf curl virus being bad in a number of areas, and whitefly feeding also caused irregular ripening on fruit in some locations.
Warm and Dry
The lack of any real winter the past several years is believed to be largely to blame for the high populations of whiteflies.
“Freezes don’t necessarily break the whitefly cycle or make them go away, but when you have a series of cold nights in the winter, it does slow them down,” Smith says. “The winter didn’t slow them down, and we also had the drought. I think the dry weather also contributed to the explosion of whitefly numbers.”
Smith says there are a number of natural fungal diseases that will help reduce the population of the pest. Those diseases will be more abundant in typical Florida conditions.
“When we had the very dry conditions over the winter, we didn’t have those diseases kicking in as much and helping to keep the whitefly in check,” he says.
Plan Around Treatment Windows
With another mild winter, there is no reason to believe whitefly infestations won’t be bad heading into spring 2018. Smith says growers should consider managing the pest in five-week treatment windows because that is roughly the lifespan of one generation of whitefly.
“When it comes to chemical control, growers need to take advantage of systemic insecticides, which have been the backbone for management for some time,” he says. “So early on (first five-week window), we want the neonicotinoids materials like Admire Pro (imidacloprid, Bayer) and Platinum (thiamethoxam, Syngenta) and other generics.”
According to Smith, Venom (dinotefuran, Valent) is a good whitefly material in the same group as the neonics. Sivanto Prime (flupyradifurone, Bayer) also has systemic activity and does a good job in whitefly control. Verimark (cyantraniliprole, DuPont) is completely different mode of action (MOA) that can be applied through drip irrigation.
Those materials will help control the whiteflies colonizing the crop and bringing primary virus transmission. The second generation of whitefly and second five-week treatment window will bring the secondary virus infection, and in tomato, nymphs can promote irregular ripening.
“We don’t want to forget about nymphs building up,” Smith says. “Knack (pyriproxyfen, Valent) is a good material preventing nymphs from becoming adults and reduces hatches,” Smith says. “Courier (buprofezin, Nichino America) is another effective insect growth regulator. Movento (spirotetramat, Bayer) is a completely different MOA that is good on nymphs.”
Smith also suggest growers don’t overlook softer materials in the biorational or biopesticide category. “Insecticidal soaps like M-Pede (potassium salts, Gowan) and distillate oils like SuffOil-X (mineral oil, BioWorks) and microbial insecticides based on Beauvaria bassiana all can contribute to whitefly control,” he says. “These products typically have to be applied repeatedly to have an effect. With some of these products, growers need to be careful of phytotoxicity, but they are good resistance management tools when incorporated into a rotation.”
There are a number of other materials that are available to manage whitefly, including botanical oil products like Ecotrol (KeyPlex). Smith encourages growers to map out a planned rotation, focusing on five-week window treatments. More on mapping out a spray program can be found in the Vegetable Production Handbook of Florida.
“The main idea of the window treatment is you don’t want to apply the same MOA in two successive generations (or window) of the same pest,” Smith says. “You don’t want to spray one generation of whitefly with a MOA and then spray the following generation with the same MOA. That is when you run into resistance problems.”