Dryland and irrigated peanuts are looking good throughout the county where we have received as much as 4 inches of rain on the east side over the past week and a half. This morning, we were checking for insects and disease. We started off looking at caterpillars. Our caterpillar threshold is 4 – 8 per row foot. We use the lower numbers for peanuts that may already be stressed. This is an irrigated where field is about 75% lapped and plants are growing well and healthy. We saw soybean loopers, armyworms and corn earworms at 6 – 7 worms per row foot. Since we are at high end of threshold, it is going to be sprayed.
The main insect issue we are watching for is lesser cornstalk borers. With the dryer weather, these caterpillars become a problem. The problem is more likely to be observed in non-irraged fields first. If you see a plant that is wilting serverely, slice into the shoot and try to locate the worm. Mitchell County Ag Agent, Andy Shirley, has a picture of LCB he took this week. You can see his blog post here: Lesser Cornstalk Borers.
Lesser Cornstalk Borer – Photo by Andy Shirley
Here is what UGA Extension Peanut Entomologist, Dr. Mark Abney, has to say:
Lesser cornstalk borer (LCB) is probably the most serious (insect) pest of peanuts in Georgia. LCB thrives in hot, dry conditions and light sandy soils. Fields need to be scouted to determine if LCB is present. When scouting for LCB, several locations should be checked in each field. The caterpillars are most easily found if you pull up the plant. Pull a few plants at each location. You will be looking for larvae, feeding damage, and silken tubes covered with soil. The larvae can be difficult to find as they will often be inside the silk tubes or inside the stems of the plant. You may also see LCB moths flushing from the peanut foliage as you walk through fields.
Granular chlorpyrifos (Lorsban 15G) is currently the only material recommended for LCB control in the UGA Pest Management Handbook. This product CANNOT be applied by airplane to peanut. Liquid formulations of chlorpyrifos are NOT REGISTERED for foliar application in peanut. Granular chlorpyrifos must have rainfall or irrigation to be effective. Chlorpyrifos will kill beneficial insects, so we should be made aware that using this product increases the risk of outbreaks of foliage feeding caterpillars and more importantly spider mites.
Additionally, previous work at UGA found foliar insecticides to be ineffective at controlling this pest. While there are several products available for use in peanut that would probably kill LCB larvae, getting the insecticide to the target will be nearly impossible. We are currently testing a variety of foliar insecticides against LCB and will provide updates if/when any new information is available.
Rainfall and cooler temperatures will slow LCB populations, but once we get into an outbreak situation, we should not expect rainfall to alleviate the problem.