Grape Phylloxera - Pest Management Program for Grape Series
Table of Contents
Grape phylloxera, Daktulosphaira vitifoliae (Fitch) is an insect pest which attacks many grape species both wild and cultivated. During feeding, phylloxera secrete a chemical which causes plant tissue to grow near the feeding site, resulting in the characteristic galls. Phylloxera is an indirect pest of grapes, damaging vines by feeding on plant sap from roots, leaves and tendrils, but not causing actual fruit injury. It is often described as an "aphid-like", sucking insect or a "vine louse".
Figure 1. Phylloxera leaf galls on De Chaunac grapes.
On cultivars susceptible to root infestation, mainly ungrafted V. vinifera, phylloxera infestations may be lethal to the vine. Infested roots swell to form root galls while the phylloxera continue to feed on the outer surface of the swollen area. Large galls on older roots are often attacked by root rot diseases, which usually results first in decline, and then death of the vine, three or four years following a phylloxera infestation. In major grape growing regions, phylloxera-tolerant American rootstocks are used to cultivate V. vinifera. In Ontario vineyards, the grape phylloxera inhabits most root systems, but has no lethal effects due to low winter temperatures which prevent excessive buildup of the phylloxera population. The root form in Ontario is currently classified as a minor pest.
Grape phylloxera adult females, both root and leaf feeding forms, are wingless and oval, 0.7 mm to 1.0 mm long and about 0.5 mm wide. On the leaves, young adults are bright yellow to orange becoming brown with age. On roots, they are pale green, light brown or orange. Newly deposited eggs are oval, bright yellow, approximately 0.4 mm long and 0.2 mm wide. Just prior to hatching. the eggs turn dark yellow with 2 visible red eye spots at one end. Emerging nymphs are similar in size to the egg. The nymphs progress through 4 developmental stages before reaching the adult stage. The winged adult female, emerging from the soil in late summer and early fall, is orange with a grey-black head and thorax with two pairs of lightly veined wings.
A. Root Cycle
On roots, phylloxera overwinter as first instar nymphs (Figure 2). In the spring, as soil temperature rises. nymphs begin feeding on root sap and mature to adults in 15 to 20 days. The spring and summer feeding adults, which are strictly females, reproduce without male fertilization. One female can produce 100 to 150 eggs over a period of approximately 45 days. New nymphs move to other root areas, begin feeding and cause gall formation. When mature, they will start producing the next generation of eggs. Five to nine overlapping generations can occur during a growing season. In September and October, newly hatched first instar nymphs begin hibernation for the winter.
Figure 2. Instar nymphs. Text equivalent of Image
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*Phylloxera are able to cause variable levels of gall formation on some V. vinifera.
Monitoring the leaf feeding cycle of grape phylloxera depends on timely visual observations. Leaf galls caused by first-generation phylloxera generally appear about mid-May, usually as one or two galls on the first to third new expanding leaves. Samples of these galls should be opened and checked with a hand lens, or better, dissected under a low-power microscope to determine when second-generation eggs begin to hatch. Two to three days after egg hatch begins is an ideal time to apply chemical control, as the new nymphs emerge from galls and crawl to the young, unexpanded leaves. The crawling and early gall development phase is the stage that phylloxera are most vulnerable to an insecticide because once new gall formation is complete, chemical control becomes difficult due to the protection offered by the leaf gall structure. Systemic insecticides may control the feeding females inside the galls; however, deposited eggs are often unaffected. Similarly, leaf galls caused by second-generation phylloxera can be sampled to determine when egg hatch begins and subsequent nymph crawling for spray timing.
Early-season chemical control may be more effective than mid- to late-season control in problem vineyards. A split-age structure in the phylloxera population develops by the beginning of the third generation, making spray timing more difficult as the season progresses. Research indicates that 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.
Common predators, including lacewing nymphs (Figure 7) and a predatory
fly larvae (Figure 8) will help to reduce phylloxera populations.
Figure 7. Lacewing nymphs are common predators of grape phylloxera.
Figure 8. Predatory fly larvae feeding on phylloxera adult and eggs inside a leaf gall.