By
Dr. John Curtis, PhD
Dr. Timothy Smith, PhD

HISTORY

         Grape phylloxera (Daktulosphaira vitifoliae Fitch) is an aphid-like insect native to eastern North America, where it infests the roots of native grapes. Native varieties (Vitis labrusca) are tolerant to phylloxera and this insect only causes minor problems. North American nursery stock was introduced into Europe during the 1850’s, inadvertently introducing grape phylloxera and rapidly infested susceptible grape varieties (Vitis vinifera) grown during this time. V. vinifera produced the great grape varieties of Europe including Cabernet Sauvignon, Pinot Noir and Chardonnay. As a result, wine-growing regions in Europe where largely devastated by this insect nearly destroying the French wine industry. This problem was eventually overcome by grafting grape vines of susceptible varieties onto the root stock of Native American grapes, since grape phylloxera does not infest roots of the latter. Subsequently, vineyards in Europe where replanted with the new grafted grape varieties. Wine connoisseurs often speculate that the pre-phylloxera wines were finer and possessed longer cellar life. Interestingly, a small part of the vineyards of Bollinger in Ay and Bouzy consists of original ungrafted Pinot Noir vines. You may try the Vieilles Vignes if you can find a bottle of this highly regarded champagne.

DESCRIPTION AND LIFE CYCLE

Winged adult phylloxera

©Image in public domain

Newly deposited eggs are lemon yellow. Nymphs are smaller than adults, but similar in color.

         Grape phylloxera can inhabit both roots and leaves of grape vines. However, mostly only root-inhabiting “biotypes” have been reported on grape vines in California and other dry-summer areas. These reproduce asexually, resulting in rootstock-specific, genetically identical strains of the insect which are called biotypes. Occasionally, winged grape phylloxera is seen, but these are believed to be non-reproductive under California conditions.

         Grape phylloxera over-winters as nymphs on roots. In spring, as the soil warms, nymphs migrate to smaller growing roots, where they begin feeding and maturing into adults. The adult deposits eggs, giving rise to three to five generations each growing season. These insects form large colonies and feed externally on roots. Nymphs are very active in the spring and can migrate through the soil, or crawl above ground to readily colonize nearby grapes, feed and reproduce. Nymphs can also be spread by water (e.g. irrigation), by blowing in the wind, or by cuttings, boots, clothing and field equipment.

         Grape phylloxera begins to hibernate in the Fall as the soil cools.

ENVIRONMENTAL CONDITIONS

         In California, grape phylloxera is mostly a problem in fine-textured soils, such as clays or clay loams, in the cooler growing regions like Napa, Lake, Mendocino, Monterey and Sonoma counties, as well as the Sacramento Delta and foothills. Soil types affect grape phylloxera mobility. Clay soils crack when dry, providing pathways for the insects to spread to infest surrounding grapes. In contrast, grape phylloxera is not a pest in sandy, well-drained soils.

DAMAGE

         Grape phylloxera damages the root system of grapes. Vine variety, age, soil type and drainage may influence the severity of infestation. Young roots are very susceptible to feeding damage and characteristically ‘swell’ when infested by this insect. During feeding, grape phylloxera may inject enzymes, causing the roots to swell. In most cases the swelling stops rootlet growth, and the affected portion dies. Swelling can also occur on larger, mature roots, but may be less obvious than smaller roots. In addition to swelling, young roots will have a ‘yellowish’ appearance and which makes it easier to identify problems. Necrotic spots (dead tissue) develop at the feeding sites on the roots. The necrotic spots are a result of secondary fungal infections that can subsequently destroy large sections of the root system.

         Root injury reduces the grape vines ability to absorb nutrients and water, causing stunting and decline in both vigor and productivity. Weakened plants become susceptible to secondary infections from fungal diseases and other insects, and to environmental stresses.

         Root injury by grape phylloxera can make it difficult to distinguish injury to the top of the vine since foliar symptoms resemble those of general root disorders (e.g. fungal diseases, nematodes). Foliar vine symptoms include reduced cane growth, short internode length, an absemce of actively growing shoot tips and premature leaf fall. These foliar symptoms can be located and monitored by remote sensing (e.g. infrared photography) to identify infected areas of vineyards. The only way to be certain that grape phylloxera has infested a vine is to examine its roots.

         It can take up to ten years from the time a plant is infested with grape phylloxera until the vine finally dies. However, during this period of decline, the quality of grapes can remain high, although the quantity of fruit gradually diminishes each year.

MANAGEMENT

Tolerant rootstock

         The use of tolerant rootstock is the most widespread and effective means for controlling grape phylloxera for more than a hundred years. Tolerant rootstock can still sustain populations of grape phylloxera, but feeding damage is minimal, compared with susceptible root stock. The use of tolerant rootstock does not eradicate this insect, but allows vines to survive in an infected area.

         Avoid rootstocks that have V. vinifera parentage because virulent biotypes of grape phylloxera may be selected and subsequently cause severe damage to vines. The biotype B damage of the rootstock AxR#1 in California is an example of this type of problem. Rootstock AxR#1 was developed during the early 1970s and planted because these solved a number of other plant pathogen problems.

         The use of tolerant rootstock also means less reliance on chemical control; maintaining the economic viability of vineyard. However, some problems with grafting have been reported such as cold injury, in regions with more severe growing conditions.

Biological control

         Biological control with natural enemies against grape phylloxera has not been well documented. In recent studies, it has been reported that grape phylloxera root damage can be somewhat reduced in organic vineyards, compared with conventional vineyards. This may be related to soils in organic vineyards that have improved organic matter and are “suppressive’ to plant pathogens. Practices which enhance soil organic matter, proper soil moisture content, and soil micro-organisms, may help control grape phylloxera.

Cultural control

         There are many cultural control practices which can reduce grape phylloxera root damage. For example, when planting a new vineyard use only clean propagating material and do not hold clean material in an infested area before planting. Young tolerant rootstock vines can still support low grape phylloxera populations and may be stunted if replanting occurs in heavily-infested soils. Buy rootstock from a reliable nursery, and use only certified vines. A susceptible rootstock in infested soil will still eventually die, despite good cultural practices.

         Phylloxera damage may be reduced by good water management, fertilization, and other cultural practices that help limit plant stress. Irrigation and fertilization practices should be designed to compensate for root loss from grape phylloxera feeding. A well-nourished and irrigated vine in deep soil, when infested, may continue to produce enough new root material to survive, even if the rootstock is only moderately tolerant. Infested vines have a lower stress tolerance and require frequent irrigation and high levels of soil nitrogen. Incorporating cover crops will also help boost organic matter, encouraging beneficial microbial activity. Removing infested vines and their roots, depriving these insects of food, and then re-planting with a vegetative cover crop for several years is another option.

         Careful sanitation of the vineyard, as well as cleaning clothing, boots and equipment (tractors etc.) when moving from an infested site to a clean one, can delay infestation, but cannot prevent the spread of grape phylloxera.

         Once grape phylloxera decline is noticed, begin to replant the block. Removal involves deep ripping, root removal, and replanting with resistant rootstocks. Soil fumigation is rarely necessary (e.g. methyl bromide). By doing this, the economic viability of the vineyard can be maintained. This can be expensive though, and may take three or four years before any economic return.

Chemical control

         Chemicals can be applied in irrigation water in drip, flood, or furrow irrigation systems. Commonly used chemicals include: Furadan 4 F (carbofuran), Enzone (sodium tetrathiocarbonate) and Admire 2 F (imidacloprid). Chemical applications will not eradicate grape phylloxera populations, especially since these chemicals cannot easily penetrate the heavy soils that this pest prefers. Large numbers of grape phylloxera can be killed with chemicals, but populations can rebound rapidly and still damage roots. It may take years of chemicals applications to control severe grape phylloxera outbreaks and so, prevention is always better than cure.