On Nov. 29, an insect capable of damaging Colorado's wine grape crop was confirmed in Mesa County. U.S. Department of Agriculture's Agricultural Research Service entomologists positively identified grapevine phylloxera (Daktulosphaira vitifoliae) on Vitis vinifera grapevines in the Grand Valley American Viticultural Area (AVA), which is a federally designated grape production area in western Colorado. Phylloxera is an aphid-like insect that feeds aggressively on grape roots.
"Nearly 75 percent of our grape acreage is in the Grand Valley AVA, which stretches along the Colorado River between Palisade and Grand Junction, and is known for its unique environment and high elevation allowing for production of world-class quality winegrapes," said Doug Caskey, Colorado Department of Agriculture's Executive Director for the Colorado Wine Industry Development Board.
In its full life cycle, phylloxera can take multiple forms. The most serious and damaging form, which was recently discovered in Mesa County, feeds on roots of grape plants. It can damage the plant by disrupting water and nutrient flow. Initially, infested plants appear weakened, stunted, and with leaves lighter in color which may look like they are suffering from a nutrient deficiency. In addition, phylloxera can live out another stage of its life on grapevine leaves. This less serious form feeds on leaves that causes leaf galls to develop, but generally not on V. vinifera.
"The Colorado Department of Agriculture and Colorado State University are actively investigating the source and working with the vineyard owner to contain and eradicate the pest. Extensive surveying is also continuing to determine the scope of the infestation," said Laura Pottorff, CDA's Nursery and Phytosanitary program manager. "Hopefully we caught this quickly enough to protect Colorado's grape crop."
Recommendations for Grape Growers
The Colorado Department of Agriculture is urging vineyard operators to contact their supplying nurseries to find out what, if any, procedures they have in place for identifying and stopping the spread of phylloxera. Colorado grape growers should also take the following precautions:
Watch plants for symptoms of chlorotic leaves, stunting and other symptoms that mimic nutritional deficiencies. If detected, sample the roots of plants for presence of phylloxera.
All harvesting and cultivation equipment should be power washed or sanitized between fields.
When purchasing grape nursery stock, request that the plants be hot water dipped prior to shipment.
Examine and inspect all new nursery stock prior to planting, or schedule an inspection by CDA staff.
Consider use of root-grafted grape nursery stock.
Colorado has approximately 150 grape growers tending 1,000 acres of vineyards and more than 140 licensed commercial wineries. These vintners produced 166,000 cases of wine during the 2016 fiscal year, which equaled more than $33 million in sales.
Phylloxera is native to the eastern and southeastern United States, where native American grape species (such as Vitis riparia and Vitis labrusca) co-evolved with the insect. Though it has spread around the world since the mid-19th century to many other wine regions, prior surveys found no evidence of phylloxera in Colorado's commercial vineyards. Grape species native to the U.S. are generally resistant to phylloxera, but V. vinifera vines have no natural resistance whatsoever. This is why phylloxera nearly wiped out all the vineyards in Europe once it survived the trans-Atlantic trip in the mid-19th century. On V. vinifera grape cultivars, phylloxera normally infests only the underground parts of the plant and eventually kills the vine. The leaf-feeding, gall-producing form is not present. In susceptible American Vitis species and hybrids, the full life cycle occurs, including the leaf-galling form. Colorado had been one of the few wine regions worldwide to not have been affected by phylloxera and as such many grapevines are self-rooted on V. vinifera rootstocks.