There are plenty of insects in Georgia peanut fields this week, but infestation levels vary significantly from field to field. The most common worm pests I am seeing continue to be soybean loopers (SBL) and velvet bean caterpillars (VBC). The VBCs have been very easy to kill in our UGA trials, and I have heard no complaints from growers, agents, or consultants. There have been problems controlling loopers in some fields. In most of the cases I have dealt with directly, we think coverage is the main culprit. Very rank peanut vines and high speed, low volume sprays can make it difficult to reach caterpillars deep in the foliage. As always it is important to scout peanut fields to assess pest populations before making a management decision.
Last Friday we did a quick lab bioassay on some SBLs that Crisp County Extension Agent Justin Lanier collected from a field that had been treated with a group 28 insecticide the previous week. These were large loopers. It took up to 4 days for the caterpillars to die, but very little feeding occurred during this time on treated leaves compared to the untreated check (see pictures below). The loopers were placed in Petri dishes with one peanut leaf and moist filter paper. Treatments were applied with a tractor mounted plot sprayer delivering 15 gallons of water per acre. The spray was allowed to dry for 2 hours, and leaves were collected from the upper canopy. The caterpillars were checked every 24hrs for mortality. After 96hrs there was 40% mortality in the untreated check and 40% mortality in the pyrethroid treatment (we know pyrethroids do not kill SBL); there was 90 to 100% mortality in all other treatments.
There have been reports of potato leaf hoppers and hopper burn. The decision to treat should be based on the amount of damage and the abundance of the insect. It is especially important to check for the immature stages (nymphs). The adults are mobile and can enter and leave a field quickly. If the nymphs are present, there is a reproducing population in the field, and they will be there for a while.
Three cornered alfalfa hoppers are still with us. We may not be there yet, but fields that are within 25 days of harvest do not need to be treated even if high TCAH populations are observed. Before 25 days pre-harvest, we use our best guess on when or if to treat. There have been reports of folks having trouble controlling TCAH this year. Rank vine growth could certainly play a role in control of this insect. The nymphs tend to be relatively stationary and spend most of their time in the lower canopy. A contact insecticide could do a decent job of killing the adults, but if the nymphs are left alive, a new crop of adults will appear within a few days giving the impression that the application had no effect.
For answers to questions about these or other insect management concerns in peanut, contact your local UGA County Extension Agent.