| | Phylloxera galls on pecans during May and early June. |
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| | Emerging phylloxera nymphs on opening pecan buds (early April). |
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| | Approximate stage of pecan bud development to start phylloxera control. |
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Pecan trees sometimes develop round galls one-fourth to 1 inch in diameter on twigs and leaves in late April, May and early June. The galls are the result of the feeding of dot-size insects called pecan phylloxera in April.
The galls generally split open in late May and early June and release small, greenish, winged aphid-like insects. The galls then dry, which causes twig dieback and leaf drop. Severe infestations of this insect can cause loss of the pecan crop for the current year and also for the following year.
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; however, control at gall split is not very effective becsause of the extended time over which the galls release insects. Spraying at gall split will not reduce any current injury to the tree, since phylloxera causes damage only during April when they start feeding on the new shoot growth. Phylloxera can damage tree appearance and reduce tree vigor; however, they rarely kill a tree unless the tree has other major problems.
Pecan phylloxera overwinter as eggs in protected places on branches. Young phylloxera resemble tiny orange aphids and appear in the spring about the time the buds unfold. The young insect inserts its beak into the new growth and injects a toxin. This causes abnormal tissue growth, which forms a gall around the insect. The phylloxera matures within the gall and deposits numerous eggs in the gall that hatch and develop into greenish winged phylloxera insects. In late May or in early June, the galls split open to release the insects. The winged phylloxera deposit eggs on bark and leaves. The eggs shortly hatch into wingless male and female insects that do not eat. These insects mate and the females produce one egg that is hidden in bark crevices.
The most effective control of pecan phylloxera is in the spring when the eggs hatch and the small insects crawl to the buds. One or two sprays in early April are usually effective in controlling this insect. Provado 1.6F, Warrior 2.56 and Lorsban 4E have given good phyloxera control.
Phylloxera usually do not spread very far from year to year; therefore good control in an orchard one year will often keep phylloxera damage low for several years.