Inadvertently imported to England and France on nursery stock between 1854 and 1860, the insect quickly invaded nonresistant Vitis vinifera wine grape blocks throughout Europe. By the end of the 19th century, grape phylloxera had destroyed two-thirds of the vineyards on the continent.

Since that time, this pest has invaded most of the grape growing areas of the world. Grape phylloxera was introduced into California in the 1850s, where it currently infests an estimated 20% of the vineyards. The British Columbia Department of Agriculture found grape phylloxera in the Penticton area in 1961; growers discovered the insect in Oregon in the early 1970s.

Grape phylloxera was reportedly found in Wash-ington in 1910, in Concord vineyards located in the Kennewick Highlands. It was again reported in 1943; this time on Vashon Island.

In 1988 the Washington State Department of Agriculture (WSDA) began surveying vineyards to determine grape phylloxera presence in the major grape growing areas of the state. This survey found grape phylloxera in eight of the 129 vineyards sampled. All but one of the findings were in Concord grapes.

The grape phylloxera, Daktulosphaira vitifoliae (Fitch), is an aphidlike insect that feeds on grape roots. The majority of adults are wingless and generally oval, but egg-laying females can be pear shaped. They vary in size from 0.7 to 1.0mm (¹/₃₀ to ¹/₂₅ inch) long and 0.4 to 0.6mm wide (Fig. 1) Color of the adults varies with the food supply: on fresh vigorous roots adults are pale green, yellowish green, olive-green or light brown; on weakened roots, they are brown or orange. Newly deposited eggs are lemon yellow.

Phylloxera can inhabit both roots and leaves of grapevines. Only root-inhabiting forms have been reported on domesticated grapes in California and Washington. Phylloxera overwinters as small nymphs on the larger roots. In spring, as the soil warms, these nymphs migrate to smaller growing roots, where they feed and mature. The mature form deposits eggs, giving rise to several generations throughout the summer and fall. Some phylloxera leave the roots on which they have fed and travel on the soil surface or through cracks to reinfest other portions of the root or roots of other vines. Hibernation begins in September as the soil cools.

Phylloxera development depends on the quality of roots, environmental temperature and humidity. In early spring and fall, nymphs mature in about 34 days. In mid-summer, the life cycle requires about 15 days from eggs to adults. The mature female lays an average of 117 eggs during her 3-week life.

In most cases the swelling stops rootlet growth, and the affected portion dies. Root injuries reduce the vines' ability to absorb nutrients and water, causing decline in vigor and productivity. Weakened plants probably become more susceptible to secondary infections from fungal diseases and other insects, and to environmental stresses.

Vine variety, age, soil type and drainage may influence the severity of infestation. Vigorous vines tolerate phylloxera attack better than weak vines. Vines growing in heavy, shallow soils succumb to infestation more rapidly than plants on lighter, well-drained soil. Experience in California shows that vines growing on light, sandy soils appear to be almost immune to phylloxera. These soils affect phylloxera mobility. Heavier soils contract and crack when drying, creating passageways for phylloxera to travel and expand the infected area.

Because phylloxera injury to the top of the vine is predominantly an indirect result of root damage, symptoms resemble those of other root disorders. Fungal root rots, gopher damage and nematodes will all cause debilitation similar to phylloxera symptoms.

In vinifera vineyards, growers first notice phylloxera where a few vines in one area show decreased vigor and premature foliage yellowing. Infected vines are more susceptible to water stress; leaves may become scorched during a period when vines require large amounts of water. Gradually, adjacent vines will show similar signs of decline, while those initially infested continue to weaken and may eventually die.

The only way to be certain that phylloxera has infested a vine is to examine its roots (Fig. 4). The best time to detect the insect is from late spring through mid-summer, when insects are more numerous, and galls or tuberosities resulting from feeding are more visible. Examine new fleshy growth on fine roots for those swollen areas. When they occur on the root tip, they are club-shaped or form crooks. The growths, initially white or yellow, later will turn dark brown, and after root death, wither and decay.

Feeding can also occur on larger roots, causing similar effects of swelling, splitting and decay. In early stages of infestation, phylloxera are easier to find on the roots than they are in advanced stages, when roots become dry or spongy, and bark begins sloughing. Infestation of roots on individual vines is not uniform. Examination of roots from different areas of the vine may be necessary to detect phylloxera presence.

Because phylloxera are extremely small, use a 10x hand lens or dissecting scope to detect the insect on roots.

Since there are no good chemical controls approved for grape phylloxera, quarantine and sanitation primarily deter its spread. Use only clean propagating material, and do not hold clean cuttings or rooted plants in infested areas before planting. Resistant rootstocks are not immune to infestation, they only tolerate the pest. They, along with Concord nursery material, can spread phylloxera if moved from infested to noninfested areas.

Many objects, such as tillage implements, stakes, tires and shoes, can also spread phylloxera. Newly hatched nymphs can live out of the soil for at least 3 days, and for more than a week submerged in water. Irrigation water may be responsible for moving migrating phylloxera. Restricting the spread of phylloxera is difficult, but in most instances is worth the effort.

The most effective management technique in major grape growing areas has been use of tolerant rootstocks. This practice does not eliminate the insect, but allows vines to subsist in an infected area. There are also problems using grafted vines in Washington, under the more severe growing conditions. In the event that a grafted variety suffers cold injury, regrafting may be necessary. This would present problems of vigorous regrowth and continued cold injury susceptibility.

In other grape growing areas that have soils similar to those in eastern Washington, infested grape vines have been productive over a normal life span. Irrigation and fertilization practices must be designed to compensate for root loss from phylloxera feeding. Infested vines have a lower stress tolerance and require frequent irrigation and high levels of soil nitrogen.

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