John R. Pyzner | 4/7/2006 1:53:39 AM
Pecan trees are sometimes infested by dot-size insects called pecan phylloxera in April. The feeding of these minuscule insects can produce round galls ¼- to 1-inch in diameter on twigs and leaves in late April, May and early June.
The galls generally split open in late May and early June and release small, greenish, winged aphid-like phylloxera. The galls then dry, which causes leaf drop and twig dieback.
Severe infestations of this insect can cause loss of the pecan crop for the current year and also for the following year, according to LSU AgCenter pecan expert Dr. John Pyzner.
No effective control of phylloxera is available once the galls are present. Sprayed insecticides will not reach the insects inside the galls, and systemic insecticides will usually not reach high enough concentrations in the galls to kill the insects.
Spraying for phylloxera after the galls split open will kill some of the insects. Pyzner cautions, however, that control at gall split is not very effective because of the extended period over which the galls release insects.
"Spraying at gall split will not reduce any current injury to the tree, since phylloxera only causes damage during April when they start feeding on the new shoot growth," Pyzner says.
Phylloxera can damage tree appearance and reduce tree vigor; however, they rarely kill a tree, unless the tree has other major problems.
The most effective control of pecan phylloxera is in the spring when the eggs hatch and the small insects crawl to the buds. Young phylloxera resemble very small, yellowish-orange aphids with dark-gray legs when they appear in the spring about the time the buds unfold.
A 10X or higher hand lens or magnifying glass is needed to see the phylloxera. The young insect inserts its beak into the new growth and injects a toxin. This injection causes abnormal tissue growth, which forms a gall around the insect. Phylloxera must be controlled before the galls enclose the insect.
An insecticide application is usually effective in controlling phylloxera when approximately ½- to ¾- inch of new bud growth occurs. This bud stage normally occurs around April 8, but weather conditions, varieties and locations can alter this date.
A second insecticide application may be needed for severe infestations. Pyzner recommends insecticides such as Provado 1.6F at 4 to 7 ounces per acre, Lorsban 4E at 1.5 to 2 pints per acre and Warrior at 3 to 5 ounces an acre for phylloxera control. Treat only those trees previously infested and those adjacent to them.
Phylloxera are delicate insects and usually do not spread very far; therefore, good control one year will often keep phylloxera damage low for several years unless infested trees are near.
For related horticulture topics, look for Gardening and Get It Growing links in the Feature section of the LSU AgCenter Web site: www.lsuagcenter.com.
Source: John Pyzner (318) 644-5865, or Jpyzner@agcenter.lsu.edu