Chapter 21

Managing Vineyard Insect and Mite Pests

Grape Phylloxera

The grape phylloxera (Daktulosphaira vitifoliae) is an aphid-like insect that is one of the most destructive grape pests worldwide. This small aphid-like pest has two forms that attack the roots (radicola) throughout the year or the foliage (gallicolae) during the growing season.

Symptoms

Root Form

The root-galling phylloxera (See Figure 21.11) damage the roots of grapevines by feeding on the roots, either on growing rootlets, which then swell and turn yellowish, or on mature hardened roots.

Foliar Form

Above-ground feeding by phylloxera typically appears first as premature leaf yellowing, but it can also occur on stems and tendrils if population densities are high.

Life Cycle

Root Form

Phylloxera overwinter on roots as small, dark hibernating nymphs that complete development in spring to become females that reproduce without having mated. Two or three generations are produced each year.

Foliar Form

In late summer, winged forms emerge from the soil and produce eggs that overwinter under the bark of grapevines. In the following spring (as early as bud break), females hatch from the fertilized eggs. The wingless female nymph crawls to a new shoot up to the growing point. From the upper surface of a young, unexpanded leaf, the nymph begins feeding on plant fluids by inserting its stylet into the leaf cell tissue. As the leaf expands, the leaf gall develops around the phylloxera, forming a hollow, peasized growth on the undersurface of the leaf in which feeding continues.

Monitoring

Root Form

Monitoring the root form of grape phylloxera is difficult to detect in an apparently healthy vineyard. Initial infestations of grape phylloxera appear as a few weakened vines.

Foliar Form

Monitoring the leaf feeding cycle of grape phylloxera depends on timely visual observations.

Pest Management

Pest Management

The root form of phylloxera is best controlled by grafting susceptible (usually European V. vinifera) varieties onto resistant rootstocks. The most favored rootstocks for imparting phylloxera resistance are derived from North American species, the most important being V. riparia, V. rupestris, V. berlandieri, and V. champini.

Applying Control Materials

There are no chemical control recommendations at this time for the root form of phylloxera. As for the leaf form of phylloxera, grapevines are able to withstand light to moderate amounts of leaf gall formation without having adverse effects on fruit quality or vine health. Therefore, chemical control is only recommended in vineyard blocks that have a history of serious leaf phylloxera problems. Chemical control is usually more effective early in the season, when the crawling nymphs are most vulnerable to an insecticide, than mid- to late-season control.

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