An outbreak of black-margined pecan aphids feeding on the underside of pecan leaflets is common in late summer. As these insects feed on pecan sap, they suck more fluid out the leaf than they can digest. Excess sap is excreted by thousands aphids and ends up coating the leaves below.
In the photo above you can see aphids feeding on the underside of a pecan leaflet. The aphids insert their mouthparts into a main leaf vein and suck sap from the tree. Adult aphids have wings while immature aphids are wingless.
The application of insecticides to control pecan aphids have largely proven fruitless. Pecan aphids develop pesticide resistance very quickly and aphid populations rebound quickly after being sprayed. In our pecan orchard, we concentrate our insect control efforts on pecan weevil and stinkbugs. Pecan aphid populations will eventually crash on their own. A good, heavy rain-shower will clean the leaves from the sticky sap and often help reduce aphid numbers.
