To understand the insect's distribution, an ongoing project over the last two years trapped and tracked silverleaf whitefly populations from Dothan, Ala., to east Georgia.
Led by University of Georgia investigators, the trapping program found six species of parasites that kill whiteflies in Georgia and collected and cultured a naturally occurring entomopathogen called Isaria fumosorosea from dead whiteflies on cotton. The wild strain is as effective or more, the study shows, as commercially available Isaria strains and more lethal than other types of entomopathogens against the silverleaf whitefly. The discovery may open new strategies to control the pest. The project has also confirmed peak silverleaf whitefly populations hit in September during cotton defoliation.
Stormy Sparks, University of Georgia vegetable entomologist, discussed, along with his UGA colleagues, discussed the project along and other observations going into the 2020 vegetable season to a packed room of several hundred growers, consultants and industry representatives at the annual Southeast Fruit and Vegetable Growers Conference in Savannah earlier this year.
In 2017, silverleaf whiteflies pretty much ate the lunches of Southeast vegetable and cotton growers, Little-to-no freezing temperatures in winter led to early infestations in vegetables which then migrated to cotton by mid-summer and back again to vegetables in the fall, leading to estimated $100 million to $200 million in damages over 2017 and 2018 to both crops. The whitefly can infect vegetables with yield-limiting viruses, too.
The insect put less pressure on growers the last two growing seasons. But with a mild winter so far in the Deep South, the whitefly remains on the industry's radar this year.
Sparks provided a rundown of newer insecticide tools available to growers this year.
PQZ, sold by Nichino America, is an Insecticide Resistance Action Committee, or IRAC, 9B insecticide with the active ingredient pyrifluquinazon, with a similar mode of action as Fulfill and Sefina insecticides, he said.
It "shows activity" on sucking insects, such as aphids and whiteflies. It stops them from feeding. "There's not a lot of data on this yet, but we're hoping it will show some impact on virus transmission," he said, adding it appears to be good on whitefly adults.
"It's not a top-tier product for whitefly immatures. We're still looking at the neonicotinoids (IRAC) and group 28 products for top-tier efficacy on immatures," he said.
Use an adjuvant with PQZ, which will help to spread it out, to get better contact on insects under leaves, he said. The insecticide comes with a broad label for major brassica vegetables, cucurbits, fruits and other vegetables, such as okra and potatoes.
Growers received in 2019 registration for two peptide-based bioinsecticides, new modes of action for them, he said. The pesticides are marketed under Spear-Lep, labeled for in-field applications and Spear-T, for greenhouse applications only. Both are broadly labelled for most major vegetables to control thrips, spider mites, aphids, whitefly and broad mite.
"It is a bio-insecticide. I haven't had a lot of experience with it, yet, but my impression is it may not be as strong as a lot of the synthetics, but it does have some activity. We're still working with seeing where we can use it best," he said.
At one to two pints per acre, Spear-Lep in combination with a Bt product provides another mode of action to handle the diamondback moth. Spear-T is used alone, but at a much higher rate.
He reminded growers about one label change this year. The uses for Closer 2SC have been transferred to Transform 50WG, which is marketed by Corteva.
The active ingredient remains sulfoxaflor and is mainly used for aphids 0.75 to 1.5 ounces per acre. It does have some activity on whiteflies at two-ounces-plus per acre, but isn't strong, he said.
"One crop this may have good impact for us is on sweet corn. We've had more consistent aphid problems on sweet corn in the last couple of years, and this gives us a very efficacious product to go with Sivanto on sweet corn," he said.