How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

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.

DAMAGE

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.

MANAGEMENT

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.

Biological Control
Little information on biological control of grape phylloxera is available; environmental and root conditions are more important than natural enemies.

Cultural Control
Avoid rootstocks that have V. vinifera parentage because virulent biotypes of phylloxera can be selected and may eventually damage these rootstocks (the biotype B damage of the rootstock AXR#1 in many counties in California is an example of this type of problem). It is necessary to use rootstocks that have strong resistance and no V. vinifera parentage for durable protection against phylloxera. Contact your farm advisor for the most recent information on local rootstock trials and suggestions on the best rootstock for specific agronomic conditions. When planting a new vineyard use only clean propagating material and do not hold clean material in infested areas before planting. Young resistant rootstock vines will support low phylloxera populations and may be stunted if replanting occurs in heavily infested soils. Contact your farm advisor for suggestions on replanting procedures.

In the hot Central Valley, phylloxera damage may be reduced by good water management, fertilization, and other cultural practices that help limit plant stress.

Organically Acceptable Methods
Resistant rootstocks are an organically acceptable management tool for this pest.

Monitoring and Treatment Decisions
Initial infestations of grape phylloxera appear as a few weakened vines. These insects are difficult to detect in an apparently healthy vineyard. Therefore, monitor vines at harvest in an area of the vineyard that has consistently displayed weaker growth, especially vines at the edges of the weak areas. Grape phylloxera are more readily identified on vines growing in poor soils because their impact is greater on these vines than on vigorously growing vines.

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.

PUBLICATION

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma County
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura County
D. R. Haviland, UC IPM Program, Kern County
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo County
Acknowledgment for contributions to the insects and mites section:
J. Granett, Entomology, UC Davis

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