Peanut Insects

July is the month when our most serious insect problems in peanuts show up. We need to watch for threecornered alfalfa hoppers, foliage feeding caterpillars, lesser cornstalk borers, two spotted spider mites, and potato leaf hoppers and just anything else that may hang out in a peanut field.

UGA Extension Extension Entomologist Dr. Mark Abney shared some things that we do know about these pests right now:

1. We tend to spray caterpillar infestations when they are below threshold. This may help us sleep better at night, but it does not provide economic benefit to the grower. There are a lot of factors that go into making insecticide applications in peanut, and not the least of these is when is the next scheduled fungicide application.

Our threshold is 4 – 8 caterpillars per row foot. We use the upper threshold when peanuts are not stressed, and lower threshold if peanuts do not look good.

Two-spotted spider mites with webbing

Two-spotted spider mites with webbing

2. Spider mites have been hanging around on cotton this year, and they can devastate non-irrigated peanuts in hot dry years. We need to be diligent about checking peanuts for the first signs of spider mite infestations. Once mites are identified in a field, we should avoid the use of pyrethroids in that field and watch to see if the mites begin to spread. If mites are moving, and the forecast calls for continued hot dry weather it is time to treat. Coverage will be critical to achieving control. A miticide application in 10 gallons of water per acre is most likely a waste of time and money; increase the water, increase the pressure, kill the mites.

Adult Three Cornered Alfalfa Leaf Hopper

Adult Three-Cornered Alfalfa Leaf Hopper – Photo by Dr. Mark Abney

3. Threecornered alfalfa hoppers (TCAH) are going to be in fields. Our threshold (research) does suggest that this insect can cause yield reduction in peanut, but I have seen some very high yielding peanuts with a lot of TCAH stem girdles. If spider mites and TCAH are in the same field, let the TCAHs eat. Anything we spray on TCAH will almost certainly make the mites worse, and that is not what we want to do. Otherwise, pyrethroids are still the first choice for TCAH in peanut.

4. I have received plenty of calls about lesser cornstalk borers in the last two weeks. The weather will be the biggest factor determining what happens from here. If it is hot and dry we could be in for problems; if we get some timely rain, populations are not likely to explode.

Lesser Cornstalk Borer - Photo by Andy Shirley

Lesser Cornstalk Borer – Photo by Andy Shirley

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