A sticky dripping substance falling from pecan trees in spring and summer can be annoying. The dripping material is called honeydew.
LSU AgCenter pecan expert Dr. John Pyzner says honeydew is produced by the yellow pecan aphid and the black margined aphid that often feed on the undersides of pecan leaves. These insects reproduce rapidly and can produce 16 to 32 generations in a season.
Louisiana usually has enough spring rain to keep aphid populations low and wash off the honeydew. Unfortunately, during dry weather, aphid populations often build up, and a lot of honeydew drips from the trees. The honeydew gets on lawn furniture, cars, people or anything else under the trees. Bees, wasps and ants can be attracted to the honeydew.
Spring populations of aphids sometimes can build up to high numbers and last about a week or two before the aphids disappear, usually around mid-May. Natural causes of aphid decline are weather, parasitic fungi and beneficial insects such as lady beetles and lacewings.
A second outbreak of yellow aphids usually occurs around mid-July. Feeding can reduce chlorophyll production in leaves and reduce leaf, stem and root growth. Aphid feeding normally does not produce any long-term tree damage.
A black fungus called sooty mold often can be found during the summer on the upper surface of pecan leaves with high numbers of aphids. Sooty mold feeds on the honeydew.
Pyzner says the mold doesn’t directly harm the tree, but it can become dense enough on the leaves to reduce photosynthesis and thus slow tree growth and lower nut production and quality.
Control measures are generally not required before late summer. Spraying late in the season and as little as possible encourages the conservation of natural enemies and reduces the chances for the aphids to develop resistance to insecticides.
Spraying yard trees for yellow aphid control is usually not feasible because spraying often kills the beneficial insects, and the aphid populations rebuild very rapidly for lack of natural enemies. This often requires multiple insecticide applications to maintain low aphid populations. The insecticides Provado 1.6F, Ammo 2.5EC, Mustang Max and Warrior can be used as aphid control sprays. Admire 2F can be used as a ground treatment in irrigated orchards.
On the Internet: LSU AgCenter: http://www.lsuagcenter.com/
Source: John Pyzner (318) 644-5865, or Jpyzner@agcenter.lsu.edu
The LSU AgCenter and the LSU College of Agriculture