I believe everyone knows that whitefly populations have been building dramatically the last few weeks. Whiteflies love hot dry weather and reproduce rapidly under our current conditions. While we are probably not as bad as we were in 2017 (maybe a month behind), we are far ahead of the last two years. Populations are higher and more widespread than our “normal” years. Adding to the concerns are reports of virus in some locations. While insecticidal control of whiteflies can impact virus spread when populations are low, high whitefly populations combined with whitefly transmitted viruses easily overloads our management systems.
Options for insecticidal control of whitefly have not changed much the last few years. The Group 4 and Group 28 insecticides are still the strongest insecticides against whitefly. Overall, Verimark/Exirel (Group 28) is probably our most consistent insecticide for whiteflies. Coragen (also Group 28) has performed well for us in the past, but there have been some indications of reduced efficacy in some cases. Keep an eye on performance and if you think it is slipping, rotate immediately (hitting a population with a product that is slipping is a sure fire way of killing that product). As for the Group 4 insecticides, most of them are still performing well. The exception appears to be Admire Pro; it has not performed very well the last three years. Venom, Sivanto Prime, Assail, Actara all appear to be working as expected. Both Group 28 and Group 4 insecticides that can be placed in the soil (root zone of the plant) will provide longer residual activity (probably 2 to 3 weeks); whereas, foliar applications generally last 7 to 10 days. As with most of our insecticides for whiteflies, these products are primarily active on young nymphs. Sivanto Prime does provide decent control of adults and Venom good suppression of adults.
The second tier, but very effective, insecticides for whitefly would include Knack and Courier (and possibly PQZ). Knack impacts egg hatch and interferes with last instar nymphs emergence as adults. Courier impacts nymphs as they molt. Both have almost no direct impact on adults. PQZ is grouped with this second tier because it has shown good control of adults. It also impacts nymphs but I lack adequate experience with this product to comment to extensively on its control of nymphs. It is definitely a product to consider in your rotation because of its control of adults.
Other products to consider in your rotation would include Movento, Oberon, and Sefina. These do have activity against whitefly and provide different modes of action for resistance management.
We are seeing a number of premix products that contain one or more of the active ingredients of products previously mentioned. These products should perform as well as the single products, assuming equivalent amounts of active ingredient is applied, and in some cases may provide some synergistic effects (again this is an area with minimal information and not well established). The newest of these is Senstar, which contains active ingredients from Movento and Knack. With premixes, as with all products, please pay attention to label restrictions. With all premixes, the product can only be used on crops where both active ingredients are labelled. For example, Knack is labelled on cucurbit vegetables, but Movento is not; thus, Senstar is not allowed on cucurbit vegetables.