Yellow Aphid Complex

The yellow pecan aphid and the black margined aphid are similar in appearance.

• Both species are yellow with black markings. The amount of black pigmentation varies with the stage of development and the time of year, but in general it increases from spring to fall.
• The cornicles on both species are reduced to pores.
• Except for the winged adults, yellow pecan aphids have long setae (hairs) that tend to stand out from the body at 45- to nearly 90-degree angles, giving the aphids a pincushion look. In contrast, black margined aphids have much shorter setae and they form less than a 45-degree angle with the body.
• Yellow pecan aphids have red eyes.

There are multiple generations of both species each year. Numbers tend to peak in spring and again in fall.

The yellow pecan aphid and black margined aphid cause similar types of damage. They are significant pests of pecan in California and can dramatically impact production and nut quality.

Both species feed primarily on the underside of leaves. Black margined aphids feed on major leaflet veins, while yellow pecan aphids feed on the network of small veins located throughout the leaf.

They damage pecan trees by extracting large amounts of photosynthate and water from leaves, which impairs the growth of shoots and roots. They also secrete large amounts of honeydew onto leaves. The sooty mold that grows on the honeydew can reduce photosynthetic efficiency.

Monitor often since aphid numbers can increase rapidly and exceed economic thresholds quickly. Begin scouting for yellow pecan and black margined aphids in May and continue every 4 to 5 days throughout shoot and nut development. Look at the undersurface of 5 compound leaves on at least 10 random trees throughout the orchard for a total sample of at least 50 compound leaves.

• Before June 1: Apply an insecticide if honeydew is accumulating.
• June 1 to August 15: Apply an insecticide if the total number of aphids exceeds an average of 20 per compound leaf.
• August 15 to leaf fall: Apply an insecticide if the total number of aphids exceeds an average of 10 per compound leaf.

Insecticides that preserve beneficial insects will decrease aphid populations over time.

Although imidacloprid is traditionally soil applied early in the season, foliar application is recommended later in the season, because imidacloprid is slowly taken up by the roots and translocated throughout the plant. By the time imidacloprid builds up to high enough levels in the leaves, aphids are already present and have damaged leaves.

Foliar application may also help to slow the development of resistance, because aphids are not subjected to sublethal doses of imidacloprid, which may be the case with soil application. Researchers have some evidence of resistance to imidacloprid in California, Texas and New Mexico. Furthermore, growers have observed what appears to be imidacloprid resistance in Arizona.