Scout developing pegs to find this pest feeding
By Ayanava Majumdar, Extension Entomologist, and
Greg Esco, Certified Crop Advisor
In 2012, cowpea aphids were observed feeding on large areas of peanut acres in a very sandy region of Florida, close to the Alabama border. There have been numerous other instances where cowpea aphids have been seen feeding on peanut pegs, but those infestations were overlooked as serious.
Cowpea aphid can be very damaging to peanuts in some areas and should be added to the existing range of soil pests that include wireworms, white grubs, whitefringed beetles, southern corn rootworms, lesser cornstalk borers and cutworms.
• Can cause darkening and deformation of peanut pegs.
• Feed in colonies and may cause hot-spots throughout fields.
• Is a known vector of peanut mottle virus and peanut stripe virus.
Identification And Host Plants
Many species of aphids have been recorded on peanuts in the past, so this is not a new invasion. An adult cowpea aphid (Aphis craccivora) is about 2 mm long with a black shiny body; nymphs are smaller and light gray in color. Cowpea aphids have white legs with black tips. This pest species is common on alfalfa, cotton, cowpea, wheat and many other crops.
Prolonged drought aggravates crop damage from insects. Many soil pests, like these aphids, may move actively in dry soil to seek optimum moisture conditions. Aphids primarily feed by sucking plant sap with their needle-like mouthparts. Cowpea aphids inject a toxin in the plants that causes tissue damage. Excessive feeding can cause darkening and deformation of peanut pegs.
Cowpea aphid is also a known vector of the peanut mottle virus and peanut stripe virus, but there is no information about the status of these viruses on current peanut varieties.
Pull back peanut foliage and examine pegs closely for black shiny aphids. At the original location of discovery in 2012, cowpea aphids were found in masses of 25 to 30 on each developing peg. An aphid colony could have more nymphs than adults, and the insects will start dispersing when disturbed.
Aphid populations are highly clumped, meaning there could be hot-spots, so scout randomly throughout the field before making a treatment decision. Also, look for the white molted skins on plant parts as an indicator of prior aphid infestation.
Imidacloprid (IRAC class 4A) is effective against aphids, leafhoppers and whiteflies. Some imidacloprid products labeled on peanuts are Sherpa, from Loveland Products, and Admire, from Bayer Crop- Science. Apply Sherpa as a directed spray to the foliage or plant base. The pre-harvest interval for Sherpa is 14 days with a five-day interval between applications.
Scout crops weekly after application to see if you need a second spray. If you find deformed peanut pegs with a lot of little white specks (molted aphid skin), then the damage is already done and rescue treatment with imidacloprid may not do much benefit.
Do not overuse insecticides to protect natural enemies and prevent resistance and regulatory issues. Contact your Extension agent or crop advisor for more information.