Vineyard losses to pest damage can be catastrophic. Managing
threats from pests that not only damage the vines and fruit
directly but also vector viruses is of extreme importance.
Invasive pests have increased in agriculture, due primarily to
the movement of people and goods. The only constant is change in the
degree to which different invasive species may threaten crops.
Grape berry moth larvae penetrate the clusters and can lead to splitting, disease infection and yield loss.
PHOTO COURTESY OF RUFUS ISAACS, MICHIGAN STATE UNIVERSITY.
Some pests become major issues in vegetable crops and orchards, signaling that vineyards may be next on their agenda. Current examples include the brown marmorated stinkbug and the spotted wing drosophila that have created major impacts in orchards, particularly in the mid-Atlantic states.
California is the leading grape producing state producing 90 percent of U.S. grapes, followed by the Northwest states of Washington and Oregon. Lake Erie region states of New York and Pennsylvania are in fourth and fifth place for grape production, and the North Central state of Michigan claims sixth place. University of California colleagues, Extension specialist Dr. Kent Daane, and UC IPM entomologist Dr. Walter Bentley, noted that an increasing number of invasive species are threatening U. S. vineyards. That thought is echoed across the country by Dr. Rufus Isaacs, entomologist at Michigan State University. Although California's grape crop dwarfs other states, grapes are an increasingly important crop in many locations.
Specific points must be considered in insect pest management programs and include the geographic area, specific pests, grape varieties and the differing impacts of the pests in different climates.
California pest issues
Mealybugs have been a problem in California vineyards for more than a century, with the grape mealybug first documented in 1900. Six species are known to exist in California and are the primary pests in table grapes. The most threatening species are the grape mealybug and the newest invader, the vine mealybug.
The grape mealybug is found in the Central Valley and the coastal grape regions, and it is also found in Oregon and Washington vineyards. The grape mealybug typically produces two generations a year. The grape mealybug overwinters as eggs or small nymphs under the bark.
Bentley, based at Kearney Agricultural Center, UC Davis, noted that the grape mealybug has been established for many years and parasites can manage the grape mealybug problem if the parasites are not killed through the use of chemicals.
The vine mealybug was found in Coachella Valley table grapes as early as 1994. It has been carried by wind, animals and farm machinery to other areas of the state. Several things about the vine mealybug contribute to its ability to be especially damaging. The vine mealybug produces four to seven annual generations, and it feeds on all parts of the vine throughout the season. The vine mealybug distributes more quickly throughout vineyards, and intense management is essential to prevent the mealybug spreading throughout vineyards.
Bentley said, "The first thing that growers must do at each harvest is to map out portions of their vineyards where they have pests. They need to be aware of where the pests are because once the pests spread, they are very difficult to manage. The second thing they must do is identify which species they have. "
Once growers have mapped their problem areas, they know where they need to place chemicals to avoid spread of vine mealybug. "We have a number of new chemicals that are less destructive to the parasites," Bentley said. He cited Admire, which is applied to the roots and taken up by the plant in about May. It must be applied through sprinklers or drip irrigation systems. A second chemical, Movento, is sprayed onto the leaves of the plant, and application is also done in the spring, usually about April. Bayer CropScience produces both Admire and Movento.
Grape mealybugs have been established for more than 100 years but are mostly managed by parasites.
PHOTOS LARRY STRAND, COURTESY UNIVERSITY OF CALIFORNIA STATEWIDE IPM PROGRAM.
Extensive pest management information and pest management guidelines are available on the UC Davis Integrated Pest Management Program website at (www.ipm.ucdavis.edu).
Northwest pest issues
While juice grapes have been grown for an extended time in Washington, which ranks as the leading juice grape producer, the state's wine grape production is relatively new, with wine grape vineyard establishment started about 30 years ago. The effect of the grape mealybug on juice grapes is not known. The wine grape vineyards, however, have been affected significantly by the pest.
Dr. Doug Walsh, WSU entomologist, noted that the grape mealybug is the predominant vineyard insect pest. "When wine grape vineyards were planted, growers brought in rootstock from other locations, and a lot came from California. It's likely that some infected root stock came in with the early vineyard plantings."
Walsh said, "The grape mealybug vectors complex viruses, which can be devastating to our wine grapes. We don't have the vine mealybug that California has, but the grape mealybug is about the same for us as the vine mealybug is down there. I work closely with Dr. Naida Rayapati, a virologist in our Plant Pathology to address the mealybug's effects in transmitting viruses to the grapes."
A comprehensive management program is practiced in Washington vineyards. Walsh said, "We use pheromone traps to help detect the presence of the male mealybug." He noted that only grape mealybugs have been identified.
Walsh noted, "Admire with the active ingredient imidacloprid is primarily used. We're in the rain shadow of the Cascades here in eastern Washington. We have very little rain, and by the end of winter the soil is very dry. It's essential that adequate irrigation is used with the application of imidaclopride." WSU Grape Program information is available at http://wine.wsu.edu.
Oregon grows wine grapes in both the warmer Rogue Valley of southwest Oregon and the cooler Willamette Valley in northeast Oregon. "We tend to have fewer insect or disease pests here in Oregon than in most other places," said Patty Skinkis, Oregon State University viticulture extension specialist. "A few of our vineyards have to do control for grape mealybugs and grape rust mite."
Japanese beetles prefer to feed on wine grapes and hybrid varieties, but vines can tolerate significant leaf injury.
PHOTO COURTESY OF RUFUS ISAACS, MICHIGAN STATE UNIVERSITY.
Skinkis noted that Oregon's mealybug concerns are similar to those of Washington, but that fewer of the pests appear to be present in Oregon. The vineyards that need to control mealybugs are located in the warmer region, and the cooler Willamette Valley region has some vineyards that must control grape rust mites. "These are very tiny and are hard to see," Skinkis said. The grape rust mites feed on tender spring shoots and are usually controlled early in the season with a sulfur and oil application. "We don't want to use anything that will damage our beneficial insects," Skinkis said.
Lake Erie and North Central regions
The insect pest creating the most economic impact east of the Mississippi River is the native grape berry moth. "It's been around forever," said Tim Weigle, IPM specialist with the Lake Erie Regional Grape Program, a joint program of Penn State University and Cornell University (http://lergp.cce.cornell.edu). Some 30,000 acres of grapes on more than 800 farms are grown in this region, and the grape berry moth is well-established.
Grape berry moths are pests for table, juice and wine grapes. They feed directly on the fruit, resulting in loss of yield, and make the vineyard vulnerable to disease. Spraying with any insecticide labeled for grape berry moth is recommended when scouting indicates the presence of the pest. Weigle said, "Some growers use organic products. We also have the newer growth regulators." Avoiding damage to beneficial insects is an ongoing concern.
A new online tool of the New York State IPM Program's Network for Environmental Weather Applications (NEWA) (http://newa.cornell.edu) to help control the grape berry moth is in trials, with several vineyards at this time in the second year of the project. Growers must spray for the pests within a short window of about seven days or less to coincide with egg hatch. Growers will enter the date at which the common wild grape reached 50 percent bloom, the closest NEWA weather station and the current date. If the bloom date isn't known, the program will establish an estimate based on historical data. The model will then calculate accumulated degree-days and forecast predicted pest management status and management recommendations. The tool was developed through collaboration among entomologists, IPM experts and a climatologist.
Japanese beetles have created a major concern, as they feed on the foliage and have been particularly devastating to new growers trying to establish vineyards. They can disrupt the leaf to fruit ratio, resulting in fruit that does not ripen. "We work with the New York Department of Agriculture and Marketing, and USDA to set up traps to identify new invasive species," noted Weigle.
The Michigan wine grape industry was pioneered in the Grand Traverse region at Boskydel Winery with hybrid varieties such as Vignoles, Seyval and DeChaunac. Interest turned to true vinifera cultivars in the mid 1970s. "These varietal choices have resulted in specific IPM challenges for our area," noted Dr. Duke Elsner, MSU Extension educator, in citing the susceptibility of these varieties to powdery mildew while hybrids are resistant.
"Our grape berry moth has great potential for trouble if it becomes more widely distributed in our area," Elsner said. "It seems we have a particular strain of species that is not responsive to commercially available pheromone lures, and therefore we have to scout for it by examining clusters for feeding."
Elsner cited Japanese beetles and rose chafer as pests that produce outside the vineyard sites. "We deal with incoming adults and have no means of lowering the numbers until they are in the vineyards," Elsner said. He noted that populations are very erratic, varying each year.
Isaacs noted that the number of invasive pests has increased and new species are of concern. "The grape berry moth drives the spraying program in Michigan," Isaacs said. Vineyards are often located next to wooded areas where wild grapes provide a wild host for the grape berry moth. Research has indicated that the great pressure of pests is at the borders next to wooded areas, and that treating only at the vineyard borders will reduce costs. Growers should combine scouting with the use of the degree-day model available online to assure more likely success. Degree-day tools are available online at www.enviroweather.msu.edu.
Customizing vineyard responses
Vineyard production has increased across the southwestern desert states of Arizona and New Mexico, in the Midwest across southern Missouri and southern Illinois, and in colder climates of Chicago suburbs and New England as well as in other states. While the percentage of the U.S. grape crop in these states is small, grapes are a specialty crop and contribute to states' economies.
Daane noted that the West Coast experiences wide differences in impacts of pests based upon the types of grapes grown, types of pests, geographic locations and climate. Those differences are even greater across the regions now producing grapes, and customizing vineyard responses to pests is essential to inhibit the spread of pests and limit economic impacts from crop damage.
Nancy Riggs is a freelance writer and frequent contributor. She resides in Mount Zion, Ill.