The peanuts look really good this season but there have been many questions about caterpillar control. Based on pheromone trap monitoring data, it appears that soybean and cabbage loopers are in the third generation with a sharp increase in soybean looper activity in recent weeks.
Corn earworms and tobacco budworms are in fourth or fifth generation; corn earworm moths were more abundant than tobacco budworms that are active at a very low level. We had very high beet armyworm activity from the beginning of the season (now in the sixth generation); fall armyworm activity is on the rise in various crops (fourth generation). We also have a very active population of velvetbean caterpillars – producers can find the large brown moths fluttering about in the canopy while scouting.
Above is a picture of peanut plots in Headland AL that looks ‘grazed’ from caterpillar feeding. Caterpillar numbers averaged one to two per foot of row – about half of the threshold levels recommended in the peanut IPM Guide. I find beat sampling to be very effective since I am able to scout for caterpillars in the top of canopy, three-cornered alfahoppers in the middle, and lesser cornstalk borers on the peanuts at each site.
Three-cornered alfalfa hopper numbers exceeded the threshold in our plots and we are evaluating new insecticides for control. Damage to peanut leaf terminals is not as threatening as damage to the pegging branches which may cause yield loss. Don’t let the nymph and adult TCAH move into the peanut canopy and stop them from getting close to the plant base. There are many good insecticides for three-cornered alfalfa hoppers – you may need one or two sprays but not too many to get them under control.
In replicated plots this year we are evaluating caterpillar control with low rates of insecticides – the overall goal is to prevent outbreak with less insecticidal materials. Data suggests very good caterpillar control with diflubenzuron (Dimilin), flubendiamide (Belt), and insecticide premix (Besiege) with residual up to 14 days even at the low rates (see graph).
Interestingly, Bt aizawai (Xentari) works really well for caterpillar control with good residual for 7-10 days; by 14 days we start seeing declining effectiveness. From these preliminary results, it appears that we can prevent caterpillar outbreak with use of a good insecticide rotation plan along with the use of other IPM tactics. Remember also that products like Belt, Radiant, Prevathon, and Besiege are locally systemic in the peanut foliage which is an added advantage.
Spider Mite Control
In an attempt to flare up spider mites in peanut plots, we sprayed bifenthrin and esfenvalerate at high rates about five days apart which flared up mites in some hot-spots but it was not enough for conducting a test (we are working on registering miticides on peanuts but need data from replicated studies to do so).
Based on conversations with producers and crop consultants, there have been some spider mite issues with the use of synthetic pyrethroid insecticides during July and August when it was very hot. Remember to use selective insecticides and reduce your field passes if you have spider mites. Spot treatment with miticides may work better than whole field chemical application. Refer to the Alabama Peanut IPM publications for detailed scouting and pest management instructions.
Economic threshold for caterpillars = Four or more caterpillars per foot of row
Economic threshold for TCAH = One adult per three foot of row 75 days to digging