Everyone knows we have ridiculous pest pressure from whiteflies this fall.
We were hoping that the rain from the recent hurricane would cause extensive adult mortality and provide some relief. While we did get adult mortality, it was not enough to help us much in vegetables. We have extremely high pest pressure in our normal “epicenter” (Tift and Colquitt counties), but the high pressure extends well beyond this area, with a recent complaint from Alabama.
Why do we have such a bad problem? Whiteflies got started earlier this year than normal, with noticeable populations in cotton as early as mid-June. Phillip Roberts usually warns me that we may be facing problems if he sees populations in cotton before the end of July. The earlier start in cotton and the hot, dry conditions of summer give them a couple of extra generations to build populations before entering vegetables. This may (or may not) go all the way back to our mild winter. While we did not experience problems in the spring crops, any whitefly carryover through the winter leads to problems in the fall.
What is working? I suspect (and it looks like it in my tests) that everything is probably working about as well as normal. We simply have overwhelming populations in many areas.
One of the biggest problems we face is that none of our insecticides really target the adult stage. Most everything we use is better on eggs or nymphs than it is on adults. Sivanto, a new insecticide from Bayer, has shown good efficacy against adults (as well as nymphs), but don’t expect great control of adults with anything, and adults will rapidly reinfest even with decent control.
Here is my take on our insecticide options:
I would hope for 2 to 3 weeks of control with these products. Adult counts will not tell you if they are working. You will get some adult mortality, but given the pest pressure in most areas you will be hard pressed to tell. To know if the products are working, you must monitor for establishment of nymphs. Adults will lay eggs, the eggs will hatch, and the nymphs must feed in order to get a lethal dose of insecticide.
While Sivanto is a different sub-group (within Group 4), I would still try and rotate main groups for resistance management. If applying two soil applications, I would use one Group 28 product and one Group 4 product>
Group 28: Coragen, Verimark
Group 4 (A and D): Admire Pro (and generics), Venom, Platinum, Sivanto
While we have more options for foliar insecticides for vegetables, I believe the Group 28 and Group 4 products are still the basis of our control programs. Other products do have fits for both efficacy and resistance management, but they are less likely to provide “stand alone” type activity. They are very good, and recommended, options within a control program.
Group 28: (Coragen, Exirel). Good activity on nymphs. Include a penetrating surfactant with Coragen.
Group 4 (A and D): Assail, Actara, Venom, Sivanto. All have good activity on nymphs and some activity on adults. Sivanto has shown good activity on adults. While Sivanto is a different sub-group, I still suggest treating these as the same for rotation purposes (this may change if resistance becomes an obvious issue). Note that imidacloprid is not suggested for foliar use. While an excellent product for soil use, it does not penetrate the leaf as well as the other products and breaks down in sunlight.
Group 7 (Knack): Knack is a growth regulator with primary activity against eggs (they don’t hatch) and last instar nymphs (they don’t develop into adults).
Group 16 (Courier): Courier is also a growth regulator, but is most efficacious against early instar nymphs.
Group 23 (Movento and Oberon): both of these products also are efficacious primarily against nymphs.
Oils and soaps: both oils and soaps will kill whiteflies if you cover them. Neither gives any residual control. Addition of oils and soaps will stick adult whiteflies to leaves and give some immediate visual satisfaction, but I suspect it is like trying to mass trap insects – it is not how many you catch that matters, it is how many are left behind. Similar to the mortality from the hurricane, the rain undoubtedly killed a tremendous number of adults, but it also left a tremendous number of adults. When using oils and soaps, coverage is essential. You can kill 100% of the insects you cover. This is obviously difficult on most of our crops. I am not saying the oils and soaps are not helping, I just suspect they are not helping as much as some might think.
Q biotype: Some of you may have heard of the Q biotype that has been found in Florida. It actually has been in Florida and Georgia for some time. The NEW occurrence is that it has been found outside of greenhouse environments. It is of concern as it is resistant to some of the insecticides we use against our “normal” whitefly. I do not think we are dealing with anything new, but we did collect adults last week and sent them off for identification.