By Michelle Moyer, WSU Viticulture Extension Specialist
Word on the Street
The 2014 vintage roared ahead this spring, with budbreak for Concord and Vitis vinifera about 2 weeks ahead of average. This trend has been holding steady, with bloom already being reported in many areas across the lower valley.
Coming out of what appeared to be a relatively benign winter, there have been several reports of vine collapse, and crown gall and Eutypa dieback outbreaks. Vine collapse is likely do to cold damage to roots. In early December 2013, continued cold temperatures combined with dry soils resulted in soil temperatures dropping into the mid 20s (°F), lower that what is typically seen in the area (30s, °F). This is why replenishing soil moisture in the fall is a critical step in mitigating cold damage. More information on mitigating and managing cold damage is at: http://wine.wsu.edu/research-extension/weather/cold-hardiness/
A cold snap in early February did cause minor bud damage in several areas; however, it may have also caused enough phloem damage in the vine to trigger crown gall expression. Aside from planting certified stock that originates from Foundation sources that use microtip propagation (i.e., the Clean Plant Center Northwest, or Russell Ranch at the Foundation Plant Services) which reduces the likelihood of crown gall infection and spread, managing cold damage is the best way to prevent gall expression in already-infected vines. If vines are expressing galls and canopy decline due to girdling, the best method is to retrain by removing older trunk tissue to below the gall. More information on crown gall management is at: http://wine.wsu.edu/research-extension/plant-health/grape-diseases/ . If you haven’t done so already, we encourage you to take our crown gall survey at: https://www.surveymonkey.com/s/2014CrownGall .
Eutypa dieback is a common trunk disease in other parts of the country where vineyards are aging. While WA has been able to avoid this disease due to our relatively young and expanding industry (and semi-frequent retraining of vineyards due to cold damage), it is starting to show up, especially in aging vineyards. If you suspect you have Eutypa, please contact Viticulture Extension (see footnotes below). Retraining consists of cutting wood (generally cordons and trunks) to 4 inches past the last instance of vascular browning. Remove the cut debris from the vineyard. More information on Eutypa can be found in the Field Guide for Integrated Pest Management in Pacific Northwest Vineyards (PNW644).
Growing Degree Days
The 2014 growing season mirrored 2013 up until early May (Figure 1). While temperatures have been fluctuating between below and above average, overall, warm nighttime lows have propelled both GDD accumulation, and vine growth, ahead.
The fear of restricted water allocation that was prominent during the early months of the year has somewhat dissipated in the lower valley, due to a reprieve by spring rains (Figure 2). Heading into full bloom, it is important to remember that severe water during this time can result in poor fruitset and cluster development. See http://wine.wsu.edu/research-extension/irrigation/ for more information on water management in vineyards.
Several adjustments and additions have been made to the WSU Evapotranspiration webpage, which is relevant for vineyard irrigation scheduling decisions. If you haven’t seen these additions, and are involved in irrigation scheduling, we recommend you take a look at these updates, located at: http://wine.wsu.edu/research-extension/weather/evapotranspiration/
Critical Window for Disease Control
As we rapidly advance towards full bloom, we are already in the “critical window” for powdery mildew disease control. Wine grape clusters are susceptible from cluster emergence until around 3-4 weeks post fruitset. Read up on powdery mildew management at: http://wine.wsu.edu/research-extension/plant-health/grape-diseases/. Also, do not forget proper fungicide rotation (based on FRAC groups), to follow best spray practices (changing nozzles, not driving too fast, using appropriate water volume), and to not stretch spray intervals during this critical window.