Better Yields Through Science

Pecan Diseases & Pests

DiseaseSymptoms, Life-cycle and Pest Management
Yellow AphidsScientific names: Yellow pecan: Monelliopsis pecanis Black margined: Monellia caryella

Aphids are small, soft-bodied insects that suck sap from pecan leaves. There are two species of “yellow” or “honeydew” aphids, the black-margined aphid, Monellia caryella, and the yellow pecan aphid, Monelliopsis pecanis. The black-margined aphid has a black stripe along the outside margin of its wings, which are held flat over the body. The yellow pecan aphid holds its wings roof-like over its body and lacks the black stripe along the wing margin. Immature aphids are difficult to identify because they lack wings. Infestations may contain both species.

The yellow pecan aphid occurs later in the season. Outbreaks of this species can cause defoliation and reduce yield and quality on most cultivars. Both species primarily feed on the underside of leaves. Black margined aphids feed on the underside of leaves 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 both shoots and roots. They also secrete large amounts of honeydew on to leaves, and the sooty mold that grows on the honeydew can reduce photosynthetic efficiency.

Yellow aphid eggs survive the winter hidden in bark crevices on twigs and tree trunks. Immature aphids, called nymphs, hatch from eggs in spring and begin to feed on newly expanded leaves. Nymphs mature in about a week and give birth to live young. All individuals are females that reproduce without males during spring and summer. In late September and October, males and females develop, and females deposit overwintering eggs.
Spider MitesScientific Names: Tetranychidae and Eriophyidae

The pecan leaf scorch mite is the most important spider mite attacking pecans. Large numbers of these tiny mites feed on the undersides of pecan leaves. Mites suck plant sap, causing irregular brown spots on infested leaves. Infestations often develop first along the leaf midrib. Damaged leaves appear russetted or scorched. Large infestations can result in leaf loss, especially if trees are under moisture stress.