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Eriophyid Mites and “Short Shoot Syndrome” in Grapes

Rust Mites and Short Shoot Syndrome in Oregon Vineyards

Dr. Patty Skinkis, Viticulture Extension Specialist, Oregon State University
Dr. Amy Dreves, Entomology Research & Extension, Oregon State University
Dr. Paul Schreiner, Plant Physiologist, USDA-ARS
Dr. Vaughn Walton, Horticultural Entomologist, Oregon State University

Short shoot syndrome (SSS), a term coined by the Oregon wine grape industry, describes a vine condition where shoots are severely stunted early in spring. It has been a sporadic problem in the coolest regions of the state for the past ten years. The first major observations of the problem were in 2001 in the Willamette Valley of Oregon and more recently in 2010 and 2011.   Research conducted in Oregon and other cool climate grape growing regions worldwide have shown a relationship of this specific type of stunting with presence of rust mites. Other factors can cause stunting of vines. However, research needs to be conducted to further understand the explicit role of mites on grapevines and potential links with vine stunting. The symptoms of SSS are observed sporadically across years and locations in the Willamette Valley of Oregon and are rarely observed in warmer regions of the state. Young vineyards seem to have the greatest occurrence of SSS related to high rust mite populations.

The first symptoms of SSS are observed as slow growing buds and stunted shoot growth very early in spring, before the shoots reach 6” in length. The basal leaves on stunted shoots appear puckered with a“drawstring” effectwhere the  leaf margin fails to expand. These leaves do not develop much further and may often abscise. Stunted shoots often have scarring on the stems, and the inflorescence may be damaged. The stems may have a zig-zag shape due to the stunting of shoot growth. In some cases, these symptoms have been associated with the presence of grape rust mites (Calepitrimerus vitis). Taking samples of tissue early season and examining them for rust mite presence is important to determine cause of the stunting. This will require collecting samples and viewing them under 40X or greater magnification. Vines with rust mite associated SSS generally have stunting occurring sporadically across a vine, with some shoots developing normally while others are stunted. In cane pruned vines, the affected shoots arise from the region of the cane nearest the head of the vine while more distal shoots appear to develop normally. This should not be confused with natural apical dominance which can cause shoots at the distal portions to grow faster than those at the head of the vine. To determine the difference, check for symptoms and the presence of rust mites. Thrips may also cause similar damage such as scarring and stunting of young vine tissues. Research in Oregon has found significant rust mite and thrips populations in vineyards early in spring, and it is difficult to determine which pest is causing specific symptoms such as scarring and stunting.

Stunted shoots observed with mite-associated SSS often outgrow the condition and resume normal shoot growth once daily temperatures increase in spring, if the shoot tip is not damaged.  Damage to the lower portions of the shoot will remain and can be observed later in the season. If rust mite populations increase in the vine canopy, they can cause stippling of leaves (early to mid-summer) and may lead to leaf blackening in mid-late summer which then leads to bronzing in early to mid fall. Stippling and bronzing have been associated with very high mite populations per leaf. Those vineyards managed with sulfur spray programs often do not have high rust mite populations or incidence of SSS.

Stunting can be caused by other factors including micronutrient deficiencies (boron and zinc), phylloxera infestation, crown gall, lack of irrigation or fertilization over time, many of which can lead to poor vine growth and nutrient/carbohydrate reserves that can cause stunting. When these factors are the cause of stunting, the pattern of short shoots is more uniform across an area of the vineyard  while SSS is usually more sporadic when related to a pest population of rust mites.

Control: It is difficult to identify control methods for SSS because of the lack of understanding of what the cause may be and how rust mites play a role in the stunting. The degree of damage that occurs as a result of mites and/or from the stunting can vary from vineyard to vineyard, and clear economic losses have not been identified. For information on how to manage very high rust mite populations, refer to the current edition of the PNW Insect Management Handbook for recommendations regarding management options.

For more information on eriophyid mites, please refer to the following resources:
Grape Rust Mites

The symptoms of SSS have been often observed on younger vines. (P. Skinkis)

The symptoms of SSS have been often observed on younger vines. (P. Skinkis)

Late summer bronzing of leaf surfaces is common with high rust mite infestation and warm summer temperatures. (P. Skinkis)

Late summer bronzing of leaf surfaces is common with high rust mite infestation and warm summer temperatures. (P. Skinkis)