Pecan trees dripping sap?

    A lot of pecan growers have noticed that the leaves of their trees look like they are constantly wet (photo at right). Touch the leaf and you'll find the leaf is covered in sticky tree sap. Park a car under a pecan tree and the windshield will soon be dotted with sap falling from the tree. Pecan tree sap is not actually dripping from leaves but, what you see is the exudate from pecan aphids.  

     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.