Grape Phylloxera

Phylloxera vitifoliae (Fitch)

The grape phylloxera is a serious pest of grapevines in Canada. It attacks leaves of susceptible varieties causing grotesque galls. Coincidental with the development of the wine grape industry, it has become an important pest wherever grapes are grown.

DAMAGE

Grape phylloxera causes the plant to form galls on the underside of leaves and occasionally on shoots and tendrils of more susceptible varieties. Leaf galls may be the size of a small pea; inside there may be one or more adult females and hundreds of eggs and hatching young. Leaf galls can become numerous. On very susceptible varieties, there may be as many as 200 galls per leaf with 50-80% of the leaves being infested. Heavily infested leaves die prematurely and fall from the vine. Defoliation can retard fruit ripening and reduce normal shoot growth. The wild grapevines appear much more susceptible than commercial wine varieties.

LIFE HISTORY

The insect overwinters in the egg stage. In early spring a female hatches and migrates to a developing leaf to feed. This causes an irritation in the plant tissues and a gall is formed. When mature, the female produces numerous parthenogenetic young that migrate to form new galls. After a few generations, some fall to the ground and burrow into the roots to feed. In midsummer, winged adults emerge from the ground to lay eggs on the vines. These develop into true males and females. After mating, the females lay a single egg on the vine, completing the life cycle.

Flight activity varies but usually occurs in late July or early August and ends by mid-September. A knowledge of the seasonal activity is valuable to protect new wine grape plantings.

CONTROL

Grape phylloxera has several natural enemies. These predators, which act as biological control agents, include green lacewings, thrips, mites, minute pirate bugs and a predatory fly. For heavy infestations consult your provincial Department of Agriculture for recommendations.

Grape phylloxera 2

What is it ?

Grape phylloxera, Daktulosphaira vitifoliae (synonym: Vitis vitifoliae) is a destructive pest of grapevine. It was introduced into Europe from North America in the 1860s, resulting in the devastation of over 2 million hectares of vines in France, known as the "great wine blight". It has spread to most vine growing areas of the world and is locally established in the UK, but is under containment.

The small, aphid-like insect feeds by piercing the plant tissue and sucking the sap, causing the plant to produce characteristic swellings or galls in response to its feeding. There are distinct foliar and root feeding forms. The European vine (Vitis vinifera) is particularly susceptible to root galling, which can result in the death of the plant. However, the roots of American species of Vitis are more resistant to phylloxera and control of the pest has been achieved in most countries by grafting vines onto resistant or tolerant American rootstocks.

What damage does it cause?

The expression of symptoms depends upon the type of vines being grown and also upon climatic conditions. Leaf galling does not appear on all varieties of vine and, as root galling is difficult to detect, an infestation may go unnoticed until it is widely established on a vineyard.

Root Galls

• Root-feeding stages are the most damaging, causing a loss in plant vigour, wilting and leaf yellowing. Vines may eventually die within 3-10 years.
  
   

• Galls are most damaging on the mature roots, interrupting the vascular system of the plant and causing root deterioration and rotting, assisted by secondary bacterial and fungal infection.
  
   

• Root stages of phylloxera can crawl through cracks in the soil surface to infest adjacent plant roots and they can also be spread by soil on boots or machinery.

• Damage is most severe on European vines growing from their own roots.
  
   

• Tolerant rootstocks will support populations of phylloxera which produce some root galling, but the root galls do not have a detrimental impact on the plant or significantly reduce grape yields.

Leaf galls

• Leaf galls mainly occur on the underside of leaves. They are initially green but become increasingly red and pronounced as they develop. They can be distinguished from the mite galls of Colomerus vitis which are green blisterlike swellings on the upper leaf surface with felty patches on the underside.
  
   

• Phylloxera leaf galls are most commonly found on American hybrid vines, such as Seyval Blanc, (a popular variety in the UK) and provide a useful indicator of potential root infestation.
  
   

• Leaf galls do not usually cause economic damage since the prolific foliar growth of vines compensates for any premature leaf drop. However, foliar stages do aid further increase in the population of phylloxera and can lead to dispersal to other vines, particularly during leaf-trimming and harvesting using machinery or by hand.

What is the life cycle?

The life cycle is complex with distinct root and foliar cycles, although in some cases the foliar cycle does not occur.

Root feeding stages can overwinter in the soil and continue an asexual cycle without leaf stages occurring. Leaf galls may be present one year but absent the next, depending on climatic conditions. The pest population multiplies rapidly throughout the growing season, with a potential rate of population increase similar to that of aphids.

The production of foliar stages depends on the species of vine and climatic conditions.

• If favourable conditions prevail, winged females may be produced in late summer. These migrate from the roots to the aerial parts of the plant where they deposit both male and female eggs. These sexual forms mate, after which the females deposit winter eggs on the bark of the vine.
  
   

• In the spring, asexual nymphs emerge and migrate to the upper leaves to feed. This feeding induces gall formation by the plant. The asexual nymphs mature into females which each can lay several hundred eggs. These in turn hatch to form more females to continue several asexual generations during the summer, building up high populations.
  
   

• In late summer many of the nymphs migrate to the roots to begin or continue the root cycle.

What should I do?

• Phylloxera can be introduced onto vines either as eggs on the stems or on infested roots. Ensure that newly imported vines are certified as free from phylloxera. A number of quarantine treatments are available for dormant vines, such as fumigation and hot water dipping.
  
   

• Only grow varieties grafted onto tolerant rootstocks, e.g. American and American hybrids. The use of tolerant varieties is the only effective means of control of this pest.
  
   

• Varieties such as Seyval Blanc are highly susceptible to foliar stages of the pest. Planting of this variety is not recommended, particularly in areas known to be at risk of phylloxera

Grape Phylloxera 3

Introduction

Grape phylloxera, Daktulosphaira vitifoliae (Fitch), is a serious pest of commercial grapevines worldwide. This tiny insect forms galls on leaves and roots of grapevines. It is believed that this insect originated in the Eastern United States, where damage is now most prevalent on leaves of French-American hybrid grapevines. High populations of foliar phylloxera can result in premature defoliation, reduced shoot growth, and reduced yield and quality of the crop.

Life Cycle

Grape phylloxera has a complex life cycle (Figure 1). They overwinter either as a winter egg under the bark of older canes or trunks or as nymphs on grapevine roots. The winter egg (Figure 1A) gives rise to the fundatrix, or stem mother, which moves to a nearby shoot tip and begins feeding. Feeding by the phylloxera elicits gall formation, and the female becomes enclosed within a small, spherical gall on the underside of the grape leaf. This parthenogenetic female is capable of producing several hundred eggs. First instar nymphs, or crawlers, emerge and move out of galls to nearby shoot tips where they begin feeding and thereby initiate formation of new galls. There are three to five generations of foliar phylloxera per season in eastern North America (Figure 1B). Throughout the summer a certain portion of the foliar crawlers move actively or passively to the soil surface. These crawlers may move through cracks in the soil and eventually reach grapevine roots.

Phylloxera may also overwinter on grapevine roots as first or second instar nymphs. As soil temperatures increase, crawlers resume feeding. Feeding by phylloxera on grapevine roots results in two types of galls. Nodosities are galls formed on small, apical rootlets which are generally thought to result in little damage to the vine. Tuberosities are galls formed on larger, older portions of the root which, if sufficiently abundant, may eventually result in death of the vine.

From July through October, some root-infesting phylloxera develop wing buds and eventually become fully winged adults. Alates emerge from the soil and deposit two types of eggs, a larger egg which results in a female and a smaller egg which gives rise to a male. These sexual forms mate and the female deposits a single overwintering egg under the bark of older canes or trunks, thus completing the complex life cycle.

Description

This aphid-like insect is very small and difficult to see with the unaided eye. Galls formed by phylloxera are more readily identified than the insects. Galls on leaves are small, spherical growths on the underside of the leaves (Figure 2), with the opening being on the top. Phylloxera feeding on roots also results in small galls either on apical rootlets (Figure 3) or on older portions of the root. These insects generally occur in groups on both leaves and roots and the yellowish color of the insect and their eggs is useful in recognition.

Damage

Feeding by root phylloxera on European grapevines, Vitis vinifera L., is potentially devastating and nearly destroyed the French wine industry in the late 1800's. The epidemic was eventually brought under control by grafting V. vinifera scions onto resistant American, Vitis labruscana Bailey, rootstocks. A major resistance breeding program conducted in Europe against grape phylloxera resulted in grape cultivars commonly referred to as French-American hybrids. French-American hybrids are important in eastern North America for wine production, but they are particularly susceptible to foliar grape phylloxera. Widespread planting of French-American hybrids in eastern North America has resulted in a heightened awareness of foliar phylloxera. Foliar phylloxera reduce net photosynthesis of grape leaves. Leaf galling by grape phylloxera causes distortion, necrosis, and premature defoliation of French-American vines. Premature defoliation may delay ripening, reduce crop quality, and predispose vines to winter injury. Grapevines heavily infested with foliar phylloxera may contribute to root infestations. Research indicates that high population densities of foliar phylloxera can result in a reduction in yield and quality of the crop. Populations must reach very high densities before yield is affected, and in most years yield will probably not be affected. It is not known, however, what impact infestations by the insect year after year have on the overall health and vigor of the vine.

Control

Few chemicals are registered for control of foliar grape phylloxera. Thiodan (endosulfan) is the standard for commercial growers, but no compounds are registered for homeowner use against grape phylloxera. (Endosulfan does burn some cultivars.)

Phylloxera crawlers can be spread on vineyard equipment. Therefore, when mechanical operations are performed, equipment should not be moved from an infested block to a noninfested block.

Infestations may also originate from wild grapevines near the vineyard, so these areas should be monitored carefully. Wild grapevines near the borders of vineyards should be destroyed if possible.

A number of natural enemies feed on grape phylloxera, but none are commercially available for use in biological control programs.