Over the last 3 weeks I have looked at fields in various stages of Silverleaf Whitefly infestation. I have met on-farm with many of you and hope that you have received the message that your cotton fields need to be monitored for whiteflies and that your pest control measures should be well thought out.
It has been difficult to get many growers to see the benefit in treating fields for whiteflies. In the past we have not seen whitefly numbers at this level until cotton is nearly ready for defoliation. This year however, we are encountering horrific numbers on vegetative cotton that has several weeks to go until it has finished producing.
In a previous post I reviewed the steps to take when scouting for silverleaf whitefly. I would like to take a few minutes to review insecticide options and their activity; in doing so I will also touch on some insecticides for stink bugs as well; as you know treating for stink bugs will likely increase issues with adult whiteflies.
This information if from our UGA Pest Control Handbook: https://www.caes.uga.edu/content/dam/caes-website/departments/entomology/documents/ga-pest-management-handbook/2017-commercial/COTTON.pdf
All chemical treatments in this book have been tested by our Extension Research personnel. They are research based and unbiased information. I say all of this to point out that there are many different mixtures being applied to cotton for whiteflies. I get calls where people ask if a chemical they are using for stink bug will kill whiteflies. Looking at the ratings here you can see that most formulations that work well on stink bugs do not do much if anything for whiteflies. The other thing to keep in mind is that when you spray insecticides in a field of cotton you are also affecting beneficial insects and parasites that kill some problem pests. I have also included the rating for each chemical as it affects these insects.
|Insecticide||Southern Green Stink Bug||Brown Stink Bug||Silverleaf Whitefly||Effect on Predators||Effect on Parasites|
Baythroid XL 1
Brigade2, Discipline 2, Fanfare 2
Courier 40 SC
Venom 70 WDG
Asana XL 0.66
Declare 1.25, Prolex 1.25
Warrior II Z 2.08, Silencer 1
Oberon 2 SC
Mustang Max 0.8
|1 – Very Effective on Pest 5- Not Effective on Pest
Effects on Beneficial and Parasites of problem pest – E – Easy; M – Moderate; and H – Hard
Remember that Insect Growth Regulators (IGR) are the backbone for controlling silverleaf whitefly. Catch them early and treat with an IGR. Give products time to work! IGR’s disrupt the insects life cycle. It prevents immature insects from reaching adulthood. If you spray an IGR you will do nothing for the adults, you will continue to see the adults in the field until they cycle out in 10 or so days. Your objective is to keep all the nymphs present on the underside of the leaves from turning into adults that will lay more eggs. The IGR’s job is to break the cycle by stopping the nymphs from becoming adults. Keep in mind the life cycle of the whitefly. If you catch them late and infestation of nymph and adult numbers are high; treat first with a product that affects all life stages and then go out with an IGR.
I know that stink bug populations may warrant treating cotton. But I caution you in saying; treat for stink bugs ONLY when they are at threshold and it is necessary. It is not a perfect world and we do not have perfect answers or situations to deal with sometimes. You have to do, what you have to do. But, all we can do is make the most informed decisions possible and do our best with what we have.