Going into what will undoubtedly be a very heavy whitefly season, everyone should be aware of the 24C label for Knack in vegetables in Georgia. While this was established for “potential” use against caterpillar pests, it may be of interest for battling whiteflies.
The 24C label allows for the reduced rate of 5 fl oz per acre, with up to 4 applications (still the same limit of 20 fl oz per acre per season) in Brassica Leafy Vegetables (cabbage, broccoli, greens, etc.), Cucurbits (all melons, squash, etc.) and Fruiting Vegetables (tomatoes, peppers, eggplant, okra, etc.).
I do not have any personal experience with the use of the lower rates against whitefly in vegetables, but experience in cotton and basic knowledge of the product suggests that the lower rate applied more frequently (minimum interval of 1 week) should provide as good or better control than the higher rate applied less frequently (2 week or longer interval). The big potential advantage is with multiple applications it is possible to keep the new growth treated without having to apply the higher rate.
As always, please keep resistance management in mind. Knack is heavily used in cotton and whiteflies do have the potential to develop resistance (resistance to knack is one of the characteristics of the Q biotype). We need to use rotations where possible. If you wish to use repeated applications of knack, I would suggest two back-to-back applications and then at least one (or two) application(s) of a different chemistry.