Peanut Entomology Abney
The insects (and mites) that really matter in peanut are greatly affected by rainfall. In this year of pretty consistent rain, lesser cornstalk borer is unlikely to pose a serious threat to the Georgia peanut crop. If the rainfall continues we will also get a reprieve from two spotted spider mite. Unfortunately, we are never far away from drought conditions in Georgia, and spider mite infestations are simmering in some cotton fields right now ready to move to peanut if conditions become favorable (i.e. hot and dry). Should mites need to be controlled, Portal and Comite are the two miticides labeled for use in peanut. On the other side of the coin are rootworms. Rootworms are the larvae of cucumber beetles (spotted cucumber beetle and banded cucumber beetle), and they thrive in the moist soil conditions that have been prevalent in most peanut fields so far in 2021. Growers with high risk fields (those with heavy soil texture and irrigation) are probably scouting or have already made insecticide applications for rootworms. Due to the abundance of rain, we are almost certain to see injury in fields that do not have a history of infestation. The only proven management tactic for rootworm is the application of granular chlorpyrifos. Rootworm injury in untreated plots in UGA research trials in Plains last week exceeded 60%. That is, more than 60% of all the pods on the plants had rootworm feeding injury. An infestation of this level is not something we want to miss or ignore. August is generally the real start of “caterpillar season” in Georgia peanuts. So far, our most common mid to late summer foliage feeders, velvetbean caterpillar and soybean looper, have been relatively scarce, but a few reports have indicated numbers might be starting to pick up. We also need to be watching for fall armyworm. Correctly identifying caterpillars is important for selecting the most efficacious and lowest cost insecticide. Three cornered alfalfa hopper populations always build late in the season, and the insect tends to like wet conditions, so expect to see a lot of them in the coming weeks. The impact of three cornered alfalfa hopper feeding on yield is variable, but no one has ever documented severe yield loss in GA-06G. I think a pyrethroid application can be justified in irrigated fields where the risk of spider mites is minimal. Even with the abundant rain in 2021, I would not treat non-irrigated fields with a pyrethroid. There are no other practical insecticide options for this insect in peanut.