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Managing a Phylloxera-infested Vineyard

Additional Fact Sheets on Phylloxera:

Contributing List of Authors: Ed Hellman. Oregon State University. This fact sheet and others on grape phylloxera were produced as a set by a phylloxera task force at Oregon State University: Bernadine Strik, Extension Berry Crops Specialist; M. Carmo Candolfi-Vasconcelos, Extension Viticulture Specialist; Glenn Fisher, Extension Entomologist; Edward Hellman, Extension Horticulture Agent; Steven Price, Post-doctoral Research Associate, viticulture; Anne Connelly, Master’s student, horticulture; and Paula Stonerod, Research Aide, horticulture. The authors of this fact sheet acknowledge the help and guidance of others on this task force.

Phylloxera infestation of an own-rooted European winegrape (Vitis vinifera) vineyard is considered to be ultimately lethal to the grapevines. The severity of infestation and progression of damage to vines, however, can differ among vineyards because of local site conditions and management practices. Vigorous vines tolerate phylloxera feeding better than weaker vines; therefore, conditions that promote vigor, such as deep, fertile soils and irrigation, may enable infested vines to live longer.

Prolonging the productive lifespan of infested vines is one management approach for dealing with phylloxera. Another approach is to slow the spread of infestation within the vineyard by altering management practices. You should use both approaches, but eventually you will have to make a decision on how long to retain the infested vineyard and when or whether to replant with vines grafted to a resistant rootstock.

Prolonging vine lifespan

Infested vines that are otherwise healthy and unstressed are better able to tolerate phylloxera feeding than low-vigor or stressed vines. Be sure to keep crop production in balance with the vigor of the vines. Overcropping is a severe stress to the vine. It also is important to maintain or improve your weed and pest management practices to prevent these stress factors from contributing to the decline of the vine. You may also consider a fertilization program to enhance vigor.

Irrigating infested vines to avoid water stress is an important tool for maintaining vigor. If irrigation is not possible, water availability can be increased by removing between-row groundcovers or replanting with a groundcover that is less competitive. Maintaining a clean-tilled vineyard, however, has several drawbacks, including a tendency to increase the spread of phylloxera by tilling, especially tilling after May.

Although your first impulse upon discovering phylloxera in your vineyard may be to pull out the visibly damaged vines, this practice does not eliminate phylloxera from the vineyard. In fact, it tends to enhance its rate of spread.

It is better to leave infested vines in the ground for as long as they are economically productive, managing them as described below. Remember that symptoms of phylloxera damage take several years to develop, and that the infestation is not likely to be limited to the area where they have been found. Furthermore, it is not feasible to remove the entire root system when pulling vines; phylloxera living on root pieces will provide a source of spread as their food supply is used up.

Slowing the spread of infestation

Experience in other viticultural regions has shown that phylloxera will eventually reach every vineyard in an infested district despite intensive preventive efforts. Nevertheless, preventive practices (See Reducing the Risk of Phylloxera Infestation) can delay initial infestations and slow their spread once they do occur. Grape phylloxera does not readily move on its own in Pacific Northwest vineyards.

Be aware that phylloxera can live on the roots of vines grafted onto resistant rootstocks. The resistant rootstock actually is tolerant of phylloxera infestations and does not die as a result of phylloxera feeding. Therefore, vines grafted to resistant rootstocks can be a source of initial infestation in your vineyard. Avoid planting infested grapevines.

Establish a strict sanitation program to ensure that no equipment (vehicles, tractors, cultivators, mowers), tools, or supplies (picking totes, buckets, stakes) move into or out of the vineyard without first being cleaned of all soil and plant debris. A common means by which phylloxera are spread is by movement of infested soil or root pieces on equipment. Sanitation practices should be followed for all vineyards, including those grafted to resistant rootstocks, because resistant stocks can support phylloxera populations. Educate all vineyard workers about phylloxera and how to prevent or reduce its spread.

Other vineyard management practices can reduce the risk of spreading phylloxera. Schedule all vineyard operations in the infested areas last. Restrict tillage to the period between November and May when phylloxera populations are at their lowest. If you decide to use clean cultivation between rows to reduce competition for water, be aware that tilling during the season is very likely to facilitate the spread of phylloxera by soil movement. Tilled aisles also increase the risk of rain or erosion moving infested soil downhill, and tillage results in more mud on boots and equipment.

No insecticide effectively controls phylloxera infestations in established plantings. One is being evaluated to slow the rate of spread. Soil treatments hold little promise, however, because of the great depths at which phylloxera occur, and because chemical penetration is poor in heavier soils. The only long-term solution to the phylloxera problem is the use of resistant rootstocks.

Analyzing your options

Several options are possible: pull out the vines after they have become unprofitable and don’t replant; replant infested blocks when they become unprofitable to manage; or replant the entire vineyard in a scheduled piecemeal replant program.

Your decision to replant an infested vineyard site should come only after you carefully consider the circumstances of your vineyard operation and business. The deciding factor should be the profitability of a vineyard block. Good recordkeeping is an invaluable aid in making this important replant decision. Review records of production, costs, and revenues for past years. Monitor the rate of spread of phylloxera and decline of vines to help you predict how long your infested block can remain profitable.

Consider also the existing features of your vineyard. Are the varieties and clones well suited to your site and the future wine market? Replanting provides an opportunity to change some of the features of your production system such as variety, clone, spacing, and training system in order to improve your production efficiency, fruit quality, or crop marketability. If you decide to replant, use only phylloxera-resistant rootstocks.