Black Aphids Invade Georgia Pecans

By Breanna Kendrick

Black aphids are small black insects that feed on the leaves of pecan trees. The area where black aphids are feeding will turn yellow and become necrotic, killing the tissues surrounding the feeding area.

Black aphids are most common later in the pecan season. Black aphids do have some populations early in the season, but are less of a problem then because of the actions of natural enemies.

Angelita Acebes is a tree nut entomologist at the University of Georgia. Her main area of work is pecan pest management, including black aphids.

Black aphids are one of the problems that growers are most concerned about. “I conducted a survey with the growers here in Georgia and asked them what they deemed serious in terms of insect pests,” explains Acebes. “Aphids are in the top three every time, primarily black aphids.”

Black aphids have been a problem for a while. The immediate solution for a lot of people would be to find out the most effective insecticide to use against this particular group of insects. Acebes says, “There are insecticidal trials that are being conducted to compare which of the commercially available materials are still effective against black pecan aphids.”

Insecticidal trials will be a part of the research as well as studying the biology of the black aphid. “I have a graduate student that will be working on the biological control part of black pecan aphids who will be trying to figure out if there are natural enemies, particularly parasitoids that would attack this aphid out in the field,” says Acebes.”Parasitoids are wasps that would lay eggs inside the aphid. As the eggs hatch within the aphid,  the larvae consumes the aphid from the inside, eventually killing the aphid…”

Ted Cottrell at the U.S. Department of Agriculture has also been working on black aphids for the last couple of years. He is investigating the effects of gibberellic acid. When black aphids are feeding on the leaves, they will turn the area of feeding activity yellow. But when Cottrell applies gibberellic acid, the acid prevents damage from the black aphid. The black aphid can still feed on the leaves, but applying the acid will keep the leaves green and inhibit the establishment of the aphids in the orchards. The treatment does not affect the aphids directly.

For black pecan aphid control, Acebes suggests, “the growers should avoid the use of broad-spectrum insecticides earlier in the season. If you do have other insects that can be controlled by these materials, try not to use the broad-spectrum insecticides because what happens is it will exterminate a lot of natural enemies that can keep the aphid populations down. Populations of aphids would grow higher earlier than usual; delaying the use of those strong broad-spectrum chemicals would help them in the long run.”

Acebes also suggests using the app MyIPM , which lists the diseases and insects that are problematic for growers of various commodities. The app provides information about pests, chemicals that can be used, and the injury that can be expected on crops.