Systemic insecticides are an effective production tool. Over 90 percent of the North Carolina peanut acreage is treated annually with phorate (Thimet) or acephate (Orthene). This eliminates the need for most foliar insecticides, unless worms or mites become a problem in August or September. Systemic insecticides are applied as a granular in-furrow at planting.
When foliar insecticides are used in addition to fungicides, spider mite outbreaks often occur if hot, dry weather, which favors a buildup, persists. The use of systemic insecticides at planting eliminates the need for foliar insecticide treatments for thrips early in the season and for leafhoppers in July and may decrease the likelihood of mite buildup. Systemic insecticides are not effective against worms, and if peanuts are attacked by worms in August and September, foliar sprays may be needed.
‘On-Demand’ Treatments
Integrated Pest Management (IPM) focuses on treating only when necessary. At-plant treatments are contrary to that idea. However, the convenience and effectiveness of these treatments make most other options less attractive. At-planting treatments provide some peace of mind because growers know that they suppress any potential early season pests (thrips and leafhoppers). However, such treatments assume that these insect pests will be present in economically damaging numbers. Foliar treatments do not seem to have as much of an impact in reducing the levels of tomato spotted wilt virus as do at-plant treatments.
On the other hand, “on-demand” foliar insecticides are used when insect populations reach or exceed a predetermined economic threshold. If insect populations are below this level, there is no need to treat; when they exceed the threshold, treatments can be applied to prevent economic damage. This approach requires a commitment to an effective scouting program.
Foliar Insecticides
A number of insecticides are labeled for use on peanuts as foliar sprays. Often, only one insecticide is needed for season-long control of foliar peanut insect pests in North Carolina. Growers should check their fields, know the pest situation and treat only as needed.
Application of Foliar Sprays
Calibrate the sprayer accurately to ensure application of the recommended amounts of insecticides. Check the calibration periodically during the season.
Spray for thrips, leafhoppers, corn earworms, fall armyworms and other foliar-feeding insects on peanuts with hollow cone or solid-cone nozzles at a minimum of 40 pounds per square inch and a total of 10 to 15 gallons per acre. Low-volume sprays are ineffective for spider mite control. Apply a minimum of 25 gallons of spray per acre for this pest, with adequate pressure for the nozzle setup on the sprayers. Many growers combine spider mite treatments with their leaf spot fungicide application. Spray volume commonly used for fungicide application (12 to 14 gallons per acre) may not be sufficient for good mite control. Change nozzles or slow down if past experience has given poor results.
Use flat fan nozzles to apply a minimum of 20 to 40 gallons of spray per acre directed at the base of the plant for lesser cornstalk borer control. Low gallonage applications for lesser cornstalk borer are an absolute waste of time. PG
Information prepared by Rick Brandenburg, Bridget Lassiter and Gail Wilkerson, North Carolina State University, and Ames Herbert, Virginia Polytechnic Institute and State University. For more information, visit www.peanuts.ncsu.edu.