The saying, “an ounce of prevention is worth a pound of cure” is actually very appropriate for virus diseases because these infections are not amenable to any curative, therapeutic, or chemical control measures. Grape growers must therefore use preventative strategies analogous to hand washing and coughing into one’s arms that minimize person-to-person spread of viruses.
Because infected propagation material is largely responsible for the spread of GLD and other diseases, the first line of defense when establishing new vineyards is to plant virus-tested grapevines obtained from reliable sources like certified nurseries. Secondly, never assume grapevines are virus-free based only on a healthy appearance. Thus, if you want to take cuttings from existing vineyards for the purpose of planting new vineyards, it is important to test samples for different viruses before doing so.
Grapevine Disease: Start Clean, Stay Clean
Sources of Virus-Tested Plant Materials
The quality of wine depends on the health of the grapevines it was drawn from. Thus, planting a new vineyard with virus-tested cuttings from a reliable source will help establish a vineyard with consistent yields and quality grapes. The Clean Plant Center Northwest at WSU Prosser provides virus-tested plant materials. Certified nurseries in Washington and Oregon also provide clean planting materials for growers. In addition, virus-tested planting materials can be obtained from Foundation Plant Services at the University of California, Davis.
Growers need to think about roguing, or removing vines infected with a virus, on a case-by-case basis that includes determining the productivity balance of a vineyard until replantings reach the stage where they can compensate for the expenses incurred. Roguing is generally one of the least cost-effective ways of disease management, but it may be the best decision after considering factors like the level of infection and age of the vineyard. For example, replacing infected vines in a young vineyard with low levels of infection is more economical than replacing infected vines in heavily infected older vineyards. Similarly, the benefits of roguing and replanting with virus-tested planting material outweigh the associated costs if this strategy is implemented during the formative years of a vineyard. Alternatively, roguing is probably not advisable if the infection is coming from neighboring vineyards.
During roguing, uproot the infected vine from the vineyard, collect all parts of the plant and incinerate. It is also advisable to remove 1–2 vines on either side of the infected vine to reduce the likelihood of secondary spread from the original source. Any suckers growing from residual roots in the soil should also be removed and incinerated. Do not take cuttings from an existing vineyard with out knowing its sanitary status for replanting. Use cuttings from virus-tested grapevines or certified nurseries for this purpose.
Controlling mealybug vectors is an effective management tactic for preventing virus infection of vineyards. Chemigation treatments with chloronicotinyl insecticides are registered for use on grapes [pesticide review: Catherine Daniels]. Contact WSU entomologist Dr. Doug Walsh (firstname.lastname@example.org) for guidance and additional information on treating grapevines for mealybug control.
Soil fumigation before planting grapevines is an effective approach for controlling soil-inhabiting nematodes, but it is only a temporary fix and not environmentally benign. Virologists instead recommend using virus-tested scion wood and rootstock and nematode-resistant rootstock cultivars as alternatives.
Contact the grape virologist at WSU for advice or questions.