2012 Vintage Update (13 April)

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By Michelle Moyer, Viticulture Extension Specialist; Gary Grove, Plant Pathologist; and Markus Keller, Research Viticulturist

Irrigation, Vine “Bleeding” and Impact on Early Season Development

Sap Flow Spring
A) Sufficient soil moisture results in positive root pressure leading to wound “bleeding”. B) Dry spring pruning wounds may be a sign of insufficient moisture. Photos by Michelle Moyer.

A sure sign of spring is “bleeding” (sap flow) from pruning wounds on grapevines.  “Bleeding” is likely caused by root pressure due to sufficient moisture uptake by the vine.  Low precipitation during the 2011-2012 winter season has resulted in low soil moisture content this spring for many locations.  Insufficient soil moisture which may result in poor root pressure, has and been associated with erratic budbreak, stunted shoot growth, and/or cluster abortion early in the growing season.  Are your vines bleeding, and if not, do you know what the soil moisture levels are in your vineyard (either high tech with neutron probes, or low tech by sight and feel)?

Irrigation channels are full for the season, so if your soil moisture content is low and you are noticing dry pruning wounds, now would be an appropriate time to consider a “pre-season” irrigation application.

New Fungicide Approved for Grape Disease Management

The WSDA has approved a new fungicide for disease management (Powdery Mildew and Botrytis Bunch Rot) in wine grapes. Luna Experience, a Bayer product, is a premix of fluopyram and tebuconazole. Fluopyram is a FRAC group 7 (SDHI) compound, while tebuconazole is a group 3 (DMI) compound. This fungicide can be used in rotation with group 11 compounds (QoI’s such as Flint, etc.) to help mitigate resistance development. NOTE: 1) The boscalid component of Pristine is also a group 7 compound, so keep resistance management guidelines in mind when using these two products. 2) This product has not been approved for use on juice grapes.

 Growing Degree Days

April 1 is the official start of the growing degree day accumulation season.  Be sure to check your local AgWeatherNet station (http://weather.wsu.edu) for updated GDD information, and check back to the WSU V&E website toward the beginning of May for GDD graphs that are updated every 7-14 days.  http://wine.wsu.edu/research-extension/weather/growing-degree-days/