How to Manage Pests
UC Pest Management Guidelines
Grape phylloxera is a tiny aphidlike insect that feeds on Vitis vinifera grape roots, stunting growth of vines or killing them. This pest prefers heavy clay soils that are found in the cooler grape-growing regions of the state such as Napa, Sonoma, Lake, Mendocino, and Monterey counties, as well as the Sacramento Delta and the foothills. Although grape phylloxera is present in the heavier soils of the San Joaquin Valley, damage may not be as severe. It is not a pest on sandy soils.
The majority of grape phylloxera adults are wingless females. They are generally oval shaped, but those that lay eggs are pear shaped. They are small (0.04 inch long and 0.02 inch wide) and vary in color from yellow, yellowish green, olive green, to light brown, brown, or orange. Newly deposited eggs are yellow, oval, and about twice as long as wide. Nymphs resemble adults except they are smaller.
Grape phylloxera overwinter as small nymphs on roots. In spring when soil temperatures exceed 60°F, they start feeding and growing. First instar nymphs are active crawlers and may move from plant to plant in the ground, on the soil surface, or by blowing in the wind. They may also be moved between vineyards on cuttings, boots, or equipment. Established phylloxera feed externally in groups on roots. In fall when soil temperatures fall below 60°F, all life stages die except the small nymphs. There are three to five generations each year.
Occasionally, winged phylloxera are seen in V. vinifera vineyards, but they are believed to be sterile under California conditions.
Grape phylloxera damage the root systems of grapevines by feeding on the root, either on growing rootlets, which then swell and turn yellowish, or on mature hardened roots where the swellings are often hard to see. Necrotic spots (areas of dead tissue) develop at the feeding sites on the roots. The necrotic spots are a result of secondary fungal infections that can girdle roots, killing large sections of the root system. Such root injury causes vines to become stunted and produce less fruit.
Severity of infestation will differ with the vigor of the grapevine as well as with soil texture and drainage. Leaf-galling forms of phylloxera that are common in eastern states are extremely rare in California vineyards.
Resistant rootstocks are the only completely effective means for phylloxera control in the most severely affected areas. A pesticide treatment will not eradicate phylloxera populations; the chemical cannot easily penetrate the heavy soils that this pest prefers. Also, effectiveness of a treatment is difficult to evaluate because although many phylloxera may be killed, populations may rebound rapidly and resume feeding on the vines. Because it may take years of insecticide treatments to reverse severe damage, treatments to prevent damage may be a better strategy than curative treatments.
In the hot Central Valley, phylloxera damage may be reduced by good water management, fertilization, and other cultural practices that help limit plant stress.
and Treatment Decisions
In North Coast vineyards infected vines may initially exhibit potassium deficiency symptoms. The infested area expands concentrically at a rate of two- to fourfold a year. Satellite infestations frequently establish downwind from larger infested areas. When searching for phylloxera, be aware that populations die out on declining vines. Therefore, concentrate monitoring efforts on the periphery of declining areas where damage symptoms are still minimal. Dig near the trunk of vines under the drip emitter and look for whitish yellow, hooked feeder roots that are galled. Examine the galls with a hand lens for the presence of phylloxera.
UC IPM Pest Management Guidelines: Grape