Grape Phylloxera

Grape phylloxera is a tiny aphidlike insect that feeds on roots of Vitis vinifera grape and certain rootstocks, 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.

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

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 UCCE 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 UCCE 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.

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

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.

	Common name	Amount per acre**	REI‡	PHI‡
	(Example trade name)		(hours)	(days)
Pesticide precautions Protect water Calculate VOCs Protect bees
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
A.	SPIROTETRAMAT
	(Movento)	8 oz	24	7
	MODE-OF-ACTION GROUP NUMBER1: 23
	COMMENTS: Multiple applications over several years reduces phylloxera numbers. To protect honey bees, apply only during late evening, night, or early morning when bees are not present.
B.	IMIDACLOPRID
	(Admire Pro - Soil)	14 fl oz	12	30
	MODE-OF-ACTION GROUP NUMBER1: 4A
	COMMENTS: Multiple applications over several years reduces phylloxera numbers. Soil moisture is important for effectiveness; follow label instructions carefully. Do not exceed 0.5 lb imidacloprid/acre per year. Remove weeds from vine row before application.
C.	CLOTHIANIDIN
	(Belay - Soil)	6–12 fl oz	12	30
	MODE-OF-ACTION GROUP NUMBER1: 4A
	COMMENTS: Apply to soil. Multiple applications over several years reduces phylloxera numbers. Soil moisture is important for effectiveness; follow label instructions carefully.
D.	DINOTEFURAN
	(Venom - Soil)	6 oz	12	28
	MODE-OF-ACTION GROUP NUMBER1: 4A
	COMMENTS: Apply to soil. Multiple applications over several years reduces phylloxera numbers. Soil moisture is important for effectiveness; follow label instructions carefully.
E.	THIAMETHOXAM
	(Platinum)	17 oz	12	60
	MODE-OF-ACTION GROUP NUMBER1: 4A
	COMMENTS: Multiple applications over several years reduces phylloxera numbers. Soil moisture is important for effectiveness; follow label instructions carefully.

**	Apply with enough water to provide complete coverage.
‡	Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI The longer of two intervals is the minimum time that must elapse before harvest.
*	Permit required from county agricultural commissioner for purchase or use.
1	Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).