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

Dr. Vaughn Walton, Associate Professor, Department of Horticulture, Dr. Nik Wiman, Assistant Professor Sr. Research, Department of Horticulture, OSU, Daniel Dalton, Faculty Research Assistant, Department of Horticulture, OSU

Brown Marmorated Stink Bug, (BMSB) is an invasive pest that has spread significantly throughout Oregon’s Willamette Valley. Since 2012, BMSB has increasingly been encountered by growers and can be found in wine grape vineyards of the Willamette Valley during the harvest period (Wiman et al. 2014), and established populations of BMSB are now found within the boundaries of nearly all Oregon AVAs. The highest risk areas include the Chehalem Mountains, Dundee Hills, Eola-Amity Hills, and McMinnville AVAs, although the risk is also increasing in AVAs located in southern Oregon and the Columbia Gorge. BMSB feed on vegetative tissues and grape berries, potentially causing contamination of wine grapes and wine quality losses.  BMSB may be moving into wine grapes late in the season because other food sources become unavailable and population levels are at their peak. BMSB also display “hilltopping” behavior in the fall, where they may aggregate at relatively high elevations for overwintering. Unfortunately, this means they will encounter vineyards and wineries. Winemakers have reported infestation of winery buildings and finding dead BMSB in fermenting wines.

Brown Marmorated Stink Bug can develop on a wide range of host plants, meaning that it can find refuge or reproduce on non-crop hosts and then spread to cultivated crops such as wine grapes. Often, BMSB can be found along vineyard borders that have host plants such as bigleaf maple, Himalayan blackberry, Oregon ash, or other species that produce abundant seeds or fruits. Fruit feeding by adult BMSB may cause direct crop loss due to berry necrosis (VMW, SCRI CAP grant report 2013). Contamination of grape clusters and taint because of BMSB defense chemicals is also concern. These taints can be persistent, and may result in market losses. Work conducted on Pinot noir has shown that trans-2-decenal, a defense compound produced by BMSB, is a contaminant present in wine that is processed with BMSB.

Populations of BMSB have continued to grow unabated, with major increases over the past two seasons because of increased distribution and long growing seasons. The extra heat units during the growing season allow more of the nymphs to reach the adult stage and then fly to overwintering sites. Furthermore, lack of cold temperatures in winter has limited mortality. BMSB pressure is predicted to increase in 2015 over levels seen during 2014. Growers are encouraged to learn to recognize BMSB to be aware of potential damage or contamination risk during the harvest season. BMSB can be scouted by visual observation of clusters with efforts concentrated on borders. Despite availability of commercial products, traps are not encouraged at this time because of lack standard monitoring protocols and inability to link trap captures to meaningful damage thresholds.

 Spotted Wing Drosophila, Drosophila suzukii (SWD), is firmly established in most Oregon vineyards (Loriatti et al. 2015). D. suzukii contributes to spoilage of wine grapes, but only under certain conditions. Our studies have shown that wine grapes are less suitable than fresh berry crops as a reproductive host for SWD. Wine grapes damaged by pre-harvest rains, birds or fungal infection are attractive to SWD, and when high population levels coincide with split grapes, SWD can affect quality of wine grapes by acting as a vector of Acetobacter spoilage bacteria.

The lack of winterkill and seasonal population models indicate that SWD will be present at high levels during harvest in 2015.  Growers should be aware that conditions suitable for vectoring of spoilage bacteria may result in an economic impact by SWD during harvest of 2015.

References

Ioriatti C., V. Walton, D. Dalton, G. Anfora, A. Grassi, S. Maistri and V. Mazzoni. 2015.  Drosophila suzukii (Diptera: Drosophilidae) and its potential impact to wine grapes during harvest in two cool climate wine grape production regions.  Economic Entomology, 10.1093/jee/tov042.

Wiman N.G., V. M. Walton, P. W. Shearer and S. I. Rondon. 2014. Electronically monitored labial dabbing and stylet ‘probing’ behaviors of brown marmorated stink bug, Halyomorpha halys, in simulated environments. PLoS ONE 9(12): e113514  doi:10.1371/journal.pone.0113514.

 

Grapevine red blotch associated virus (GRBaV) is a concern to grape growers throughout the state.  The virus has been present in vines for many years- however, it was formally identified and a diagnostic assay developed in 2012.  In late 2014, a group of growers, nursery operators, OWRI faculty, and ODA plant health scientists convened to share information, provide an overview of the grapevine virus situation in Oregon vineyards, and strategize future steps.  Dr. Bob Martin, USDA-ARS plant pathologist, described his GRBaV survey results- GRBaV has been detected in the Willamette Valley, but is more widespread in vineyards in southern Oregon and recent sampling indicates that the virus moves very slowly from vine to vine, if at all.  For example, of 100 vines tested in a Willamette Valley vineyard planted in the 1970’s, only one positive plant was identified in a block of Chardonnay adjacent to a small block of Pinot noir that was completely infected. Similarly, 30 samples each of Grüner veltliner and Pinot gris adjacent to an eight year old severely infected Syrah block were all negative. If funding is secured, Dr. Martin will continue to investigate the spread of red blotch and its effects on wine quality.  Dr. Vaughn Walton, OSU entomologist, reported that vector identification studies are on-going in California, but very little is known about red blotch vectors or transmission.  The focus of his research is to monitor location and spread of the disease.  Studies are also being conducted in southern Oregon to assess the spread of the disease in that environment.

For more information regarding the research in southern Oregon, please click here to read a research report from Dr. Vinay Pagay and Dr. Bob Martin.

One question that may ease growers’ minds is that nurseries are now testing for red blotch.  One nursery owner said that 3,000 tested vines in WV yielded no positive results but southern Oregon had positives in the cultivars Tempranillo, Mourvedre and Merlot.  It is possible that red blotch has spread through planting stocks, either nursery materials or from top-working plants with wood from field sources. Education on how to stop the spread of the disease will be a key component of red blotch outreach efforts.

The movement of vines and the ODA plant quarantine system, which states that it is illegal to move known infected plant materials into or within the state is an important component in stopping the spread of infected vines.  95% of Oregon grapevine nursery stock comes from California, therefore potentially infected plants may have arrived prior to the testing for GRBaV.  Nursery managers from Sunridge and Duarte noted that the new Grapevine Foundation Block at Russell Ranch (where all material has been tested using the 2010 protocol for grapevine disease testing) will become the primary source of wood for certified nurseries. All material at the Russell Ranch tested negative for GRBaV in 2013.  This part of the discussion generated two practical recommendations to grape growers:

  • Plant only certified grapevine materials. Vines from Russell Ranch and Clean Plant Center Northwest (Washington State University-Prosser, WA) are certified free of GRBaV, Grapevine leafroll associated viruses and viruses causing trunk diseases.
  • Unless individual vines are tested for known viruses, do NOT propagate from any vines in your vineyard. The risk of spread of viruses, even from asymptomatic vines, is too great.

Geoff Hall, viticulturist from Ste. Michelle Wine Estates stated that WSU faculty and industry associations consistently reinforce the need to exercise caution and utilize proper practices when managing the spread of viruses in vineyards, which applies to Oregon growers as well.

Outcomes from this important meeting include:

  • A letter has been drafted to Oregon Department of Agriculture Director Katy Coba requesting that grapevine red blotch associated viruses be added to Oregon’s plant quarantine list
  • ODA plant pathologists together with the Oregon Wine Board will apply for an ODA specialty crop block grant to do a survey of red blotch in Oregon vineyards
  • OSU will continue to provide extension resources on grapevine viruses
  • This group will serve as a vine improvement committee for the Oregon wine industry
  • There is a need to enhance grower outreach and education on grapevine viruses
  • Identify resources to increase virus testing capacity in Oregon

This group has agreed to meet again in December 2015.

Reference resources:

  1. ODA’s grapevine quarantine regulations can be found at http://arcweb.sos.state.or.us/pages/rules/oars_600/oar_603/603_052.html
  2. National Clean Plant Network Red Blotch Fact Sheet: http://cemendocino.ucanr.edu/files/165430.pdf