There are five periods during the growing season when growers using a deficit irrigation strategy need to pay close attention to the vine and soil water status, says Dr. Russell Smithyman, viticulture research director at Ste. Michelle Wine Estates.

Bloom to fruit set—If high temperatures occur during bloom, growers may need to meter small amounts of water to avoid a reduction of fruit set. You can overdo stress at bloom time. But this is the same period when you want to slow down shoot growth, so don’t apply too much water. A few hours may be all that’s needed to save your crop.

Fruit set to mid-July—Stress is desirable at this period because it will help control canopy growth. High temperatures now are helpful in slowing down canopy growth so that average shoot length is three to four feet.
Veraison—Scientists do not know the cause of sour berry or berry shrivel, but it often shows up at veraison. Some believe that stress could be a factor in this grape disorder.

Preharvest—Small amounts of water right before harvest can alleviate berry dehydration and avoid yield loss during an extended hang time.
Excessive climate conditions—Growers should always know the weather ­forecast so they can be prepared for extreme temperatures.