New Pest Invades Western Vineyards
Virginia Creeper leafhopper has few predators, can denude vines
According to a UCCE news release, VCLH have been detected in vineyards from the Oregon border to the northern Sacramento Valley, northern Sierra foothills and Lake and Mendocino counties—mostly in backyard vines and organic vineyards. None have been reported in Sonoma or Napa counties. Neither have there been any visual signs or manifestations of the bug in Oregon, according to Patti Skinkis, extension viticulturist for Oregon State University, who visits vineyards throughout the state.
The extension released a video that clearly depicts the appearance, habits and differences between VCLH and native leafhopper species.
Rhonda Smith, viticulture farm advisor for Sonoma County, speculated that because VCLH is well suited to cold climates it may be advancing south from British Columbia, where it has been studied by researchers at the Pacific Agri-Food Research Centre (PARC) in Summerland. “It has no problem with cold temperatures,” Smith told Wines & Vines. “We don’t know how well it will establish in warmer sites.
“It’s rare that a grower—organic or conventional—in the North Coast has to spray for vineyard pests, except for the exotics. That’s because of the parasitoid wasps, which provide a natural control,” Smith explained.
Exotic aliens like the VCLH don’t normally bring their own predators with them, which is what renders them more dangerous. In the case of VCLH vs. western grape leafhoppers, the parasitoid wasps haven’t learned to recognize the eggs laid by female VCLH on the underside of grape leaves as many as three generations per year.
Western grape leafhoppers lay individual eggs, while VCLH lays a string of up to seven on the leaves. “The tiny female wasp crawls along the bottom of the leaves, patting the leaf with her antenna. When she feels an egg, she lays her eggs in that,” parasitizing and destroying the leafhopper eggs. Apparently, the VCLH multi-egg is not yet a target incubator for the wasps.
“Without effective controls, VCLH populations can reach very high levels,” UCCE warned.
Although it is a “C” rated pest and not reportable, Smith recommended that pest control advisors and viticulturists monitor for VCLH when inspecting vineyards.
What the Midwest knows
Though VCLH is new to the West, the Midwest has experience with the pest. The IPM (integrated pest management) team at Ohio State University’s Department of Entomology published useful information about VCLH in its publication “Insects and Mite Pests of Grapes in Ohio and the Midwest.”
“Adults and nymphs feed on leaves by puncturing the leaf cell and sucking out the contents. Each puncture causes a white blotch to appear on the leaf. In heavy infestations, the leaves turn yellow or brown, and many will fall off. Feeding by these leafhoppers may reduce the photosynthetic capacity of the plant, and the quality and quantity of the fruit may be affected,” according to the document.
The good news: “Grapevines can tolerate populations of up to 15 insects per leaf with little or no economic damage.” And the disclaimer: “Heavy leafhopper feeding may result in premature leaf drop, lowered sugar content, increased acid and poor coloration of the fruit. The sticky excrement (honeydew)…affects the appearance and supports the growth of sooty molds. Severely infested vines may be unable to produce sufficient wood the following year.”
Leafhoppers in general “have few natural enemies,” and they tend to overwinter in weeds and vineyard debris, so maintaining a clean vineyard is recommended.
VCLH takes its name from a favored host, the Virginia Creeper, a widely planted ornamental vine also known as “false grapes.” It rarely causes substantial damage on these, although insecticidal soaps may effectively be applied. Now that VCLH has discovered “true grapes,” especially late-producing cultivars, vigilance is the best defense.
“This is not a pest you spray prophylactically for,” Smith stressed. UCCE specialist Dr. Lucia Varela is scheduled to present more information in her “Pest and Disease Update” in Yountville, Napa County, on March 6, 2013.