Cotton aphid numbers have been steadily increasing over the last several weeks. Aphids generally build to moderate/high numbers and eventually crash due to a naturally occurring fungus. This fungal epizootic typically occurs in our area in early/mid-July. Once the aphid fungus is detected in a field we would expect the aphid population to crash within a week or so (notice gray fungus in picture below).
Dr. Philip Roberts stated today that the aphid fungus is beginning to show up in southwest Georgia. Hopefully, it will make it to our side of the state within the next week or so. However, it is a judgment call whether to spray for aphids in cotton. I have observed some bad cases of aphids in cotton fields and they are beginning to effect the new growth through the loss of moisture and nutrients. Another factor that has to be considered is the late planting of some of the cotton crop and it definitely does not need to be delayed – regardless of the reason. This stress factor can be reduced with the use of an aphid insecticide. However, research conducted by Dr. Roberts in Georgia fails to consistently demonstrate a positive yield response to controlling aphids. If you decide to spray for aphids in your cotton, please be cognizant of beneficial insects in your insecticide selection and their importance as we move through the growing season.