Organic grape growers in Mendocino and Lake County have been experiencing severe outbreaks of the Virginia creeper leafhopper (Erythroneura ziczac) since 2011. Feeding by E. ziczac causes leaf stippling and reduced photosynthesis which can impact crop yield and quality. High populations of E. ziczac adults in the fall can also be a nuisance, flying into the eyes, nose, and mouth of workers manually harvesting grapes. The primary natural enemies of E. ziczac are the small egg parasitoids Anagrus daanei and Anagrus tretiakovae (Hymenoptera: Mymaridae). A related pest, the Western grape leafhopper (Erythroneura elegantula) is also parasitized by A. daanei as well as Anagrus erythroneurae. Erythroneura ziczac and E. elegantula are commonly found together in North Coast vineyards. Anagrus daanei is the parasitoid species of most importance for E. ziczac control, whereas A. tretiakovae is rarely found in California.
Our approach to improving E. ziczac control involves a combination of short-and long-term strategies. Short-term work focuses on grower outreach/education to improve pest identification and timing of chemical controls while long-term strategies are focused on the identification, evaluation and introduction of Anagrus parasitoids to improve biological control.
In 2015 we held multiple outreach events (March 6 and November 20) and a field day (July 29) to review E. ziczac identification, management and provide updates on research progress and findings to date. There were also presentations made about the importance of leafhoppers in general in the transmission of grape “red blotch”. We also initiated a regional monitoring program to keep growers informed about the seasonal development of leafhopper populations in Mendocino County. Each week, at multiple vineyard sites, data were collected on adult leafhopper flights, egg deposition, nymph densities and parasitism rates. A summary of this data was then circulated to growers via a weekly email newsletter (http://ucanr.edu/sites/vclh/VCLH_Newsletter/). Finally, we established a project website (http://ucanr.edu/sites/vclh/) to serve as a repository of information on management of E. ziczac.