Spring Gardening News Distributed 02/22/08
Pecan trees are sometimes infested by dot-size insects called pecan phylloxera in April. The feeding of these minuscule insects can produce round galls one-fourth 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 horticulturist 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 will often kill some of the insects; however, Pyzner says 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.
Phylloxera can damage tree appearance and reduce tree vigor. Pyzner points out, though, that they rarely kill a tree, unless the tree has other major problems.
The horticulturist says that 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 magnification 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 one-half to three-fourths of an 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 seven to 10 days later may be needed for severe infestations. 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 have produced good phylloxera control. Only those trees previously infested and pecan trees nearby should be sprayed. Spraying yard trees is difficult for homeowners because of the size of most pecan trees and the availability of the insecticides in small quantities.
Pyzner notes that 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.
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On the Internet: LSU AgCenter: www.lsuagcenter.com
Contact: John Pyzner (318) 644-5865 or Jpyzner@agcenter.lsu.edu
Editor: Mark Claesgens (225) 578-2939 or mclaesgens@agcenter.lsu.edu