Drought Management
With so many vineyard sites in central Washington State experiencing drought conditions and water interruptions, perhaps it's prudent to talk about what to do in this upcoming growing season.
Lack of water can affect grapevines in a number of ways; however the greatest effect is on flower bud initiation and fruit set. Since grapes are perennial woody crops, under severe stress the vine will put more of its energy into storage and survival than fruit production. Studies conducted on orchard trees during the drought of 1977 indicated that severe pruning and fruit removal were successful in mitigating the effects of drought. Several existing studies have examined the effect of seasonal water deficits on grapevine growth, and all of them come to one main conclusion: the period of growth about three weeks before bloom and fruit set is highly sensitive to water deficit, as is the period of inflorescence initiation. Inflorescence initiation happens between bloom and fruit set (possibly a little beyond), and it's during this time that the flower buds for next year are being differentiated in the latent buds of the leaf axils. Severe deficits during this period can lead to problems with pollinization, specifically male sterility (pollen).
How do you manage your water that you do get? Try and water during the important periods of plant growth, at the beginning of the season (fill up soil profile), before bloom and fruit set, and around veraison. Be sure to also fill up the soil profile in the fall so that vines will head into the next growing season with some water in the profile. We may still have more dry winters like 2004-2005. If you are with an irrigation district that has senior water rights and have a drip system with continuous water, irrigate in short sets. If your irrigation district has junior water rights that are interruptible, be sure to water when you have it in long sets to fill the soil water profile thoroughly. Targeting irrigation applications for the critical periods in plant growth is important for both wine and juice grapes; however, be sure to water juice grapes thoroughly when you have water available. Canopy and fruit demands outweigh that of wine grape varieties.
Alternative water sources should be considered, including re-using tailwater in furrow-irrigated systems, digging emergency wells (contact your local Department of Ecology office), stream water, and storage water. The FSA is currently offering low-interest loans for infrastructure improvements, including upgrading to more efficient irrigation systems. Crop insurance may also help to soften the blow from this year's drought.
In order to still have a successful growing season, make sure to:
• Control canopy growth early in order to avoid a high water requirement later in the season;
• Reduce weed growth in the vineyard to avoid competition for water resources;
• Keep cover crops mown or spray with herbicides in severe situations;
• Thin heavy crops to lower crop loads to ensure that it will ripen satisfactorily.
For more information, be sure to check out the drought publication for grapes, http://cru.cahe.wsu.edu/CEPublications/em4831/em4831.pdf
- Dr. Mercy Olmstead
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