By Dr. Ayanava Majumdar, Peanut Entomologist,
Alabama Cooperative Extension System
In 2012, reports on aphids feasting on peanut pegs were confirmed in many areas, including the panhandle of Florida. It is likely that drought contributed to the infestation and lack of adequate control of the minute pest.
Although many species of aphids have been recorded on peanuts, adult aphids found had a black shiny body; nymphs were smaller and light gray in color. Preliminary identification indicated them to be cowpea aphids, A. craccivora, a common pest species on alfalfa, cotton, cowpea, wheat and many other crops. Common weed species for aphids include dandelion, lambsquarter, pepperweed, pigweed and others.
Dense Feeding Clusters
Aphids were found on the pegs in dense colonies consisting of adults and nymphs feeding together. Pull back the peanut foliage and examine pegs closely for one or more black aphids. At the location in Santa Rosa County on sandy soil, aphids were found in masses of 25 to 30 adults and nymphs feeding.
Aphids will start dispersing if touched, and populations are highly clustered in some parts of the field, so scout randomly throughout the field and not just one location. Also look for the white molted skin on plant parts.
Aphids primarily feed by sucking plant sap with their needlelike mouthparts. Cowpea aphids inject a toxin in the plants. There will be darkening and deformation of peanut pegs when aphid numbers are high. Cowpea aphid is also a known vector of the peanut mottle virus and peanut stripe virus.
Pest pressure can be estimated based on the number of damaged pegs and area affected. Populations generally stay in check from the presence of natural enemies, but outbreaks can happen by use of contact insecticides that eliminate natural enemies. Scout for insects and make insecticide treatment decisions based on proper identification, economic thresholds, weather and crop growth conditions.
In general, imidacloprid (insecticide class 4A) is effective against aphids, leafhoppers and whiteflies. Some products that are labeled on peanuts for aphid control include Sherpa, Loveland Products, and Admire, Bayer CropScience.
Admire, with 21 percent imidacloprid, can be used early in the season as an in-furrow spray below the seed. Sherpa, with 17 percent imidacloprid, can be a directed spray to the foliage or base of the plant and seems to be a cost-effective product.
At the field site examined for aphid outbreaks, two applications of Sherpa at 3.5 ounces per acre reduced aphid infestations significantly.
Scout crops two to three days after application to see if you need a second spray. Imidacloprid will not affect caterpillars and mites, so keep scouting for those pests. If you find deformed peanut pegs but no live aphids, then the damage is already done, and rescue treatment may not do much.
Identification Is Critical
Seek assistance from Extension personnel, providing insect samples, for correct identification, which is key for effective integrated pest management. For insect images, subscribe to the Alabama Peanut IPM Project on Facebook. To subscribe to the Alabama IPM newsletter, email email@example.com.