Rust Mites Can Cause Damage Shortly After Budbreak
Dr. Patty Skinkis, Viticulture Extension Specialist & Associate Professor
Grape rust mites have been a nuisance pest in vineyards of western Oregon for years. They can be found living on grape tissues from early spring through summer. Grape rust mite has been known to cause shoot deformity early in the growing season with most notable damage in years when vines have delayed growth under cool conditions.
Being aware of the first signs and symptoms of rust mite infestation in early spring is important to determine if there is a problem. However, visual symptoms are not enough for action. It is critical to determine presence of grape rust mites before considering application of miticide sprays. The presence of high numbers of rust mites have been found to cause severe stunting of emerging buds and young shoots. For examples of these symptoms, see the grape rust mite section of the PNW Insect Management Handbook. There can be numerous other causes of stunted shoots, but with the hype of rust mite concerns, many growers blamed rust mites as the cause of all stunted shoots. As a result, there have been potentially unnecessary applications of miticides (sulfur, lime sulfur, stylet oil, or other miticide products) early in the season.
Grape rust mites are impossible to see with the naked eye, so tissue collection and viewing under magnification is required. A user-friendly method was recently developed by a team at the OWRI to monitor grape rust mites on vine tissues. This method has since been employed by growers in Oregon to determine presence of rust mites. The protocol is available for use and links provided below:
Using this method, we were able to determine a strong correlation of rust mite presence on stunted shoots early in the season. Damaged shoots often had hundreds of mites; there were over 100 mites found on shoots <10 cm in length using the rinse in bag protocol and up to 500 mites when evaluated upon subsequent extractions (Schreiner et al. 2014). Since there can be great variability in mite numbers and rapid growth of tissues early season, it is difficult to determine clear action thresholds. However, action is warranted if there is significant shoot stunting, deformity and confirmed high populations of rust mites. In-season sulfur sprays that are applied as a means to prevent powdery mildew has been found to keep rust mite populations in check (Schreiner et al. 2014). Current recommendations exist for early season rust mite control, and those can be found in the 2015 Pest Management Guide for Wine Grapes in Oregon.
For more information about monitoring for rust mites and management, see the following publications and resources:
Schreiner, R.P., P.A. Skinkis, and A.J. Dreves. 2014. A rapid method to assess grape rust mites on leaves and observations from case studies in Western Oregon vineyards. HortTechnology. 24: 38-47.
Skinkis, P.A., J.W. Pscheidt, E. Peachey, A.J. Dreves, V.M. Walton, I. Zasada, R. Martin, D. Sanchez, and C. Kaiser. 2015. 2015 Pest Management Guide for Wine Grapes in Oregon. OSU Extension Publishing. https://catalog.extension.oregonstate.edu/sites/catalog.extension.oregonstate.edu/files/project/pdf/em8413_0.pdf
Skinkis, P. 2014. Grape Rust Mites, eXtension/eViticulture.org. http://www.extension.org/pages/33107/grape-rust-mite#.U_yZCHcXOVo
Skinkis, P., J. DeFrancesco, and V. Walton. 2015. Grape Rust Mite, PNW Insect Management Handbook. http://insect.pnwhandbooks.org/small-fruit/grape/grape-grape-rust-mite