Tuesday, May 24, 2011

Pecan Phylloxera Attacks Backyard Trees

The pecan phylloxera is a small, aphid-like insect that is rarely seen, but the galls it produces are prominent and easily noticed.  This year the pecan phylloxera is common, and we have gotten many calls about this problem.  The numerous light green galls, often described as bumps or blisters on the pecan leaves, alarm many homeowners who are worried that it might be the beginning of a serious problem.  Fortunately, this looks worse than what it is, and it rarely causes serious problems for the pecan tree.

Pecan phylloxera have a complicated life cycle for an insect.  The pecan phylloxera overwinters as eggs located inside the dead body of a female adult, which is in protected places on the branches of pecan trees. Soon after bud break, the eggs hatch and the young insects migrate to opening buds or leaf tissue to feed on expanding new growth. These individuals feed in such a way that it stimulates the development of galls, which encloses the phylloxera insect in a few days. Inside the gall, she matures, lays her eggs and dies. These eggs hatch within the gall, and these nymphs feed within the gall until they mature. The gall provides protection from predatory insects that would normally decimate their population.

In early July, the galls split open and the mature nymphs emerge as winged, adults. These adults migrate to other trees or other parts of the same tree and lay eggs that are of two sizes. The smaller eggs hatch into males, and the larger eggs hatch into females. These male and female phylloxera do not feed; their sole purpose is to produce the overwintering eggs. This final stage of the insect seeks out sheltered places on a tree, where they are protected for the winter.  The adults and nymphs are small, one-eighth inch long, soft-bodied and cream-colored. They resemble aphids. You'll need a hand lens to observe and identify them.

Once the galls appear, it is too late to control pecan phylloxera for the season. However, in most cases it is not necessary to be concerned, since they usually do not cause enough damage to pecan trees to warrant an insecticide application. Spraying large backyard trees is usually not practical in any case.  Certain native trees and grafted varieties within an orchard may become more heavily infested than other trees.

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