Grape phylloxera (Viteus vitifoliae) is a type of aphid found on the roots of grapes or in galls formed on the leaves of wild grapes and some hybrid varieties. It is native to eastern North America.
European vinifera varieties are particularly susceptible to this pest, and the accidental introduction of phylloxera to California, Europe and elsewhere initially devastated these industries. Management of phylloxera with insecticides was not successful, and the wine grape industry was only rescued with the development of resistant rootstocks derived from American Vitis species or hybrids between these and susceptible V. vinifera.
Phylloxera were first identified in the Penticton area in 1961. Infestations currently are scattered and at relatively low levels, mostly due to the use of resistant rootstocks and the failure of this pest to thrive on sandy soils.
Phylloxera were discovered infesting leaves of hybrid grapes on Vancouver Island in 2020, but the extent and severity of the infestation is not yet known.
As early as 1914, it was recognized that grape phylloxera consisted of several distinct biotypes or races. Biotypes differ in their ability to form galls on the leaves of certain cultivars, in the degree of feeding damage caused to roots and their propensity to form sexual or winged forms.
One study demonstrated that rootstocks with unsatisfactory levels of resistance to phylloxera in Europe and South Africa were suitable for California, Australia and New Zealand. Loss of resistance can also occur over time as new biotypes of phylloxera arise.
Adults are very small, usually wingless, and less than 1 mm long and half as wide. Colour varies from pale green, yellowish-green or light brown on vigorous roots, to brown or orange-brown on declining roots. As adults age, they become a darker brown or even purplish-brown. Winged sexual forms are rare in B.C. and the northwestern U.S., and they do not appear able to reproduce sexually on vinifera grapes.
Leaf galls are formed on French-American hybrids, Concord juice grapes and some rootstocks. The relatively small galls on the undersides of leaves are green and roughly circular. These should not be confused with the white or brown fuzzy galls of variable sizes and shapes formed on the undersides of leaves by erineum (leaf blister) mite.
Phylloxera overwinter on roots as eggs or small, dark hibernating nymphs that complete development in spring to become females that reproduce without having mated. Two or three generations are produced each year.
When populations are large or the vines are declining, some newly hatched nymphs leave the roots through cracks in the soil and migrate to the roots of nearby vines. These small crawlers have been known to climb vine trunks and be blown on the wind for some distance.
In late summer, a portion of the nymphs develop into winged females (alates) that leave the soil and fly to other vines, where they lay eggs in the crevices in the bark that hatch into both males and females. After mating, these late summer females produce a single, larger overwintering egg.
In spring, the eggs hatch into females that feed on developing leaves and produce galls on susceptible varieties.
Nymphs produced in the galls can infest other leaves or migrate down to the roots. Most grapes grown in B.C. are not susceptible to leaf galls, and the life cycle here largely consists of asexual forms confined to the roots of grapes. For this reason, infestations spread at a relatively slow rate.
Feeding by phylloxera on the roots of grapevines results in severe water and nutrient stress and eventual death of the vines. Roots become stunted and galled and die prematurely from the injection of harmful saliva and invasion of fungal pathogens.
Depending on vine vigour and the size of the infestation, vines can slowly become stressed and chlorotic, or they can decline rapidly.
Vines that fail to thrive and become chlorotic and unproductive should be inspected for the presence of phylloxera. Galls on leaves are an obvious indication of phylloxera on hybrid varieties.
However, damage confined to roots of vinifera wine grapes can be confused with damage from nematodes or root diseases. To determine the cause of damage, carefully expose the roots and search for the typical swellings and dying roots caused by phylloxera. A hand lens or dissecting microscope will help verify their presence. Areas of vineyards with phylloxera will appear as expanding patches of severely stunted or dying vines.
Insecticide treatments were previously not effective, and there are no spray thresholds for phylloxera on roots. Hybrid cultivars that develop leaf galls are better able to tolerate or resist feeding damage to roots, but elimination of the leaf gall forms soon after they are detected might help reduce the extent of the infestation.
For more information about insecticides, see the Pesticides page.
Biological control of phylloxera has not been studied in detail.
A number of generalist predators are known to feed on phylloxera in leaf galls. In Ontario, larvae of two species of predaceous flies were commonly associated with leaf galls. Predaceous soil-dwelling carabid beetles undoubtedly feed on phylloxera infesting roots, and, because they do not produce honeydew, ants are likely to feed on phylloxera rather than protect and milk them as they do aphids.
Natural enemies and diseases are not thought to provide effective control of phylloxera established on roots of susceptible vinfera vines.
When establishing a new vineyard, purchase plants from reputable suppliers and ensure that planting material is healthy and free of phylloxera. Vines imported into B.C. are given a hot water treatment to prevent the importation of phylloxera and other grapevine pests.
To ensure that phylloxera are not moved from infested to clean areas on farm machinery, disinfect all equipment. Less frequent cultivation is thought to be helpful.
Resistant rootstocks provide an effective means of combating phylloxera. Almost all resistant rootstocks were developed from crosses between several species of wild grapes native to eastern and southern North America (V. riparia, V. rupestris, V. berlandieri and others). Some of the grape rootstocks with good phylloxera resistance that are commonly grown in B.C. include SO4, 5BB, 5C, 420A and 161-49C.
Rootstocks vary in characteristics such as vigour, and it is often difficult to select an appropriate rootstock for a particular vineyard. Soil types, resistance to nematodes, vine spacing and several other factors need to be considered in addition to phylloxera resistance. Prior to planting, it is advisable to read appropriate publications and consult with vineyard managers or consultants. A more complete listing of phylloxera-resistant rootstocks that includes other characteristics can be found on the Rootstocks page.
Vigorous vines resist phylloxera damage better than stressed vines. Provision of additional water and nutrients can help delay the rate of decline. Infested vines should not be heavily cropped, and extra care is required to prevent additional stresses from insects and diseases. Some varieties are more vigorous and are better able to resist damage.
Phylloxera infestations are more damaging and spread more rapidly on heavier soils that are prone to cracking, while vines planted in sandy soils can be nearly immune to attack.
