Damage: Phylloxera are tiny, soft-bodied insects closely related to aphids. These insects cause conspicuous swellings, called galls, to form on leaves, twigs and nuts. The two most important species attacking pecans are the pecan leaf phylloxen and the pecan phylloxera. The pecan leaf phylloxera forms galls on leaves only and extensive infestations may cause some defoliation. The pecan phylloxera is the most damaging species because it attacks the shoots and nuts. Extensive infestations of this species can destroy the nut crop and reduce the tree's vitality and subsequent production.
Biology: Phylloxera survive the winter as eggs in bark crevices. In spring, the tiny nymphs emerge during budbreak and feed on new growth. Nymphs secrete a substance while feeding that stimulates plant tissue to develop abnormally, creating galls. The young phylloxera are soon completely enclosed in the galls, which range in size from 1/10 inch to 1 inch in diameter. Phylloxera feed inside the gall and complete two generations. Galls then crack open and winged, adult phylloxera emerge to lay eggs.
In the case of the more destructive pecan phylloxera, no additional galls are formed. Females hide in protected places on the bark and die, with their eggs remaining inside the protective bodies of the mothers throughout the winter. Some adult females of the pecan leaf phylloxera which emerge from spring galls may also overwinter. However, other females lay eggs and the hatching nymphs form a second or third generation of galls during one season, if new growth is available.
Control: Native trees and improved varieties vary in their susceptibility to phylloxera. Phylloxera can not fly far and infestations move slowly from tree to tree. For these reasons, control is often achieved by treating only those trees with phylloxera galls. Survey the orchard in May and mark trees with galls for treatment the following spring.
Insecticides for phylloxera must be applied after egg hatch in the spring but before nymphs are protected inside galls. Treat after bud break when growth is 1 to 2 inches long. Phylloxera infestations also can be reduced with a dormant oil spray applied to tree trunks and limbs during the dormant season. Thorough coverage is essential to en- sure that eggs are killed.