Examples of a root damaged by phylloxera, top, and healthy root, below. (Courtesy Jack Kelly Clark, University of California Statewide IPM Program)
An extensive search for certain destructive grape pests in Washington State last year turned up no invasive moths, but it did find a surprise detection of grape phylloxera, says an entomologist for the Washington State Department of Agriculture.
The trapping and sampling was one of the most extensive grape surveys yet by WSDA. Nearly 3,200 traps and samples of soil, roots, and leaves were used to survey the major grape producing regions in the state, as well as Puget Sound and the San Juan Islands. WSDA hung more than 2,500 pheromone traps in vineyards in 18 counties looking for four exotic moth pests, as well as the destructive soil phylloxera pest, vine mealybug, and a fungal grape disease known as rotbrenner or red fire.
The traps, designed to attract European grapevine moth, European grape berry moth, grape tortrix, grape leafroller tortrix, and vine mealybug, came up clean.
“We found none of the exotic grape moths or vine mealybug,” said Michael Klaus, WSDA entomologist.
European grapevine moth has been a concern since the nation’s first detection of the moth in California’s Napa Valley in 2009. Thus far, the moth has not been found anywhere else in the United States. Vine mealybug, another relatively new species in grape production, has spread throughout California, but has not yet been detected in Washington.
Leaf samples from nearly 350 vineyards were tested for rotbrenner, with no positive results.
Some 154 soil and root samples were analyzed by WSDA for grape phylloxera, a time-consuming process of washing material, using a series of sieves to catch the tiny insect, and finally using DNA extraction. Soil and root analysis was completed in mid-December. Grape phylloxera is a tiny aphid-like insect that feeds on Vitis vinifera grape roots, stunting growth of vines or killing them.
The soil/root tests confirmed grape phylloxera in a Wapato Concord vineyard, where a live nymph was found in the summer survey and a nodule was then observed on roots. Soils samples later analyzed confirmed the presence of phylloxera. Phylloxera was found in the same vineyard in a 1988 survey and again in 2002.
But the soil tests revealed a positive phylloxera find in a new location—a wine grape vineyard south of Wenatchee. “This is an unexpected new site and possibly a new county record,” Klaus said in an email.
Grape phylloxera was first found in the state in 1910 in Concord vineyards near Kennewick. It was again reported in 1943 on Vashon Island. In 1988, WSDA began surveying vineyards to look for the pest. The survey found grape phylloxera in 8 of 129 vineyards sampled. All but one of the eight findings were in Concord grapes. Seven of the eight vineyards that tested positive for phylloxera in 1988 have since been removed.
Although other wine regions, such as France and California, have suffered from phylloxera infestations that nearly wiped out wine grape production and caused expensive replanting, the pest has never caused economic damage in Washington. Klaus believes that the state’s sandy soils have kept the pest in check in Washington.
“Phylloxera like heavier, clay soils,” he said, adding that when the clay soils dry and crack, crawlers move out of the soil and are easily dispersed by equipment and people. “There is a leaf form, but we don’t have it in eastern Washington.” Phylloxera is a tiny, soil-borne aphid that mainly feeds on roots. By feeding on the roots, the pest weakens vines and reduces vine productivity.
WSDA will be working with industry groups and Washington State University entomologists this spring to determine a course of action in response to the new phylloxera find.
Many questions need answering, says Klaus. Where did the plant material come from? If from out of state, did it pass through nursery stock inspection? Was it from certified plant material? What is the age of the vineyard? Is it planted on rootstock? Are other vineyards in the area?
More samples of the vineyard need to be taken to further delineate if phylloxera is in the area, but details about who pays for further sampling will need to be worked out, he said. The original survey was funded from a specialty crop block grant included in the Farm Bill.
Klaus presented initial survey findings during the annual meeting of the Washington State Grape Society. •
Melissa Hansen is the research program director for the Washington Wine Commission. Hansen previously was an associate editor at Good Fruit Grower from 1996 through 2015. Read her stories: Author Index