In its 2019-20 fiscal year, the Oregon Wine Board of Directors granted $417,000 to researchers for nine projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let you know about the status of these projects.

Dr. Vaughn Walton is a professor and horticultural entomologist in the Department of Horticulture at Oregon State University. He has prepared the update below.

This project also receives funding from the California Department of Food & Agriculture and the USDA Specialty Crop Research Initiative.

Improved understanding of virus transmission and management of key vector(s) associated with Grapevine red blotch virus

Project objectives:
The objective of this study is to improve understanding of the transmission of grapevine red blotch virus and management of key vectors associated with transmitting the virus.

The specific project objectives are to:

  1. Determine virus status of plants subjected to transmission biology assays from 2016-2018
  2. Conduct refined transmission biology trials
  3. Evaluate conventional and cultural control strategies of key treehopper species
  4. Evaluate behavioral management techniques for key treehopper species

Importance to the Oregon wine community:
The Oregon wine industry is concerned about grapevine red blotch virus because of reduced grape berry quality and rapid spread. With up to tenfold increase of virus incidence across three seasons, management is critical to the sustained health of Oregon vineyards.

Progress so far:
Virus transmission
We conducted controlled transmission trials from 2016-2019 to determine the ability of treehopper populations to transmit grapevine red blotch virus (GRBV). We tested three treehopper species: Spissistilus festinus (Say), Stictocephala basalis (Walker), and Tortistilus albidosparsus (Stål). All of these collections were made in close proximity to commercial vineyards in Oregon. We also tested immature insects of St. basalis in 2018.

Only Sp. festinus successfully transmitted GRBV in one case. We found that virus particles were present in the petiole tissue of a leaf basal to the feeding leaf following a 24-hour inoculation access period. This successful transmission was verified using quantitative PCR (qPCR) and also the more sensitive droplet digital PCR.

We also used qPCR to test insects to see if GRBV can persist in them after uptake. We determined that GRBV could persist inside the bodies of all three treehopper species. More Sp. festinus successfully acquired virus particles compared to the other species.

Overall, our results did not provide evidence that St. basalis or T. albidosparsus can transmit GRBV. Of particular interest were the findings that GRBV transmission by Sp. festinus was rare.

Vector management
Chemical control trials resulted in lower insect populations, but it is too early to show correlation between the spread of the virus and insect control. Controlled cover crop trials showed that wild mustard did not support treehopper development. Behavioral studies were successful to replicate vibrational communication as well as attraction of St. basalis.

Next steps:
We plan to conduct additional transmission biology studies on other species of leafhoppers and treehoppers. We plan to conduct additional follow-up testing of plant materials. Three manuscripts are currently being prepared for publication.