Cotton aphid numbers were slow to get started this year, but have been increasing rapidly over the last couple of 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.
I asked Dr. Philip Roberts yesterday about the aphid fungus being present in southwest Georgia. He stated, “The fungus has started in southwest Georgia and has been observed as far east as Hazelhurst.” Hopefully, the fungus will make it to Bulloch County next week. 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. This stress factor can be reduced with the use of an aphid insecticide. However, research conducted by Dr. Roberts in Georgia (graph below) 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.
Lets hope the fungus shows up sooner rather than later and eliminates the aphid issue. Please let me know if you have questions.