By Michelle Moyer, WSU Viticulture Extension Specialist
Growing Degree Days
The 2014 growing season is still mirroring the warm 2013 vintage, albeit we are slightly ahead of last year (Figure 1). While hot temperatures in the coming week will substantially add to the vintage GDD accumulation, remember that vines begin to shut down at temperatures above 95°F. For those doing leaf removal now, be cautious of fruit exposure during periods of high heat: sunburn is a result of both sun exposure AND high temperatures.
Precipitation is still below normal for the growing season, despite several rain events in May and mid-June (Figure 2). With most vineyards past fruit set and beginning deficit irrigation practices, the lack of forecast rain bodes well for canopy management through strategic irritation implementation. See http://wine.wsu.edu/research-extension/irrigation/ for more information on water management in vineyards.
Early to mid-June rain events slightly increased disease pressure in Eastern WA, but overall, pressure has remained at low-to-moderate levels as we progress towards the end of the susceptible period for powdery mildew. More information on general disease management can be found at: http://wine.wsu.edu/research-extension/plant-health/grape-diseases/ .
Many actively growing vineyards can exhibit nutrient deficiency symptoms at this time of the season. There have been several reports of nitrogen deficiency symptoms, typical in rapidly growing canopies or in vines suffering from early and severe water stress (a common problem in rain-fed vineyards where supplemental irrigation is not present during dry periods). In addition, phosphorous deficiencies (reddening of older leaves, starting at leaf margins) can begin to show now. Phosphorous deficiency can look similar to virus symptoms; timing of symptoms is often an early distinguisher (virus symptoms begin to show later in the growing season). If your vines are exhibiting potential nutrient deficiency symptoms, consider a tissue test in a month or so, when véraison starts. See: http://wine.wsu.edu/research-extension/plant-health/nutrition-and-soils/ for more information in nutrient management.
Viticulture Extension Events:
Upcoming Viticulture Extension events are posted at: http://cahnrs.wsu.edu/events/category/grapes-wine/month/. Save the date for the annual Washington State Viticulture Field Day co-hosted by Washington State University and the Washington State Grape Society: 15 August 2014!