California North Coast Irrigation Initiation Guidelines
Recent rainfall has alleviated the need for early irrigation initiation. Avoid the temptation to begin irrigation, as vines will become accustomed to the easily-extracted irrigation water once it becomes available. Let them use stored water reserves in the soil for as long as possible before initiating the irrigation “season”. Premature irrigation initiation can result in cane lengths that need hedging and lateral shoot initiation that increases the costs of canopy and disease management.
· Keep an eye on cover crops (if they exist). Deeply-rooted perennial grasses (e.g. Blue Wild Rye, California Brome) will dry up and go dormant when soil water reserves become low. Don’t be concerned, however, when annual grasses and legumes and less drought-tolerant perennial grasses get brown.
· Monitor soil moisture, if you have devices installed. Soil moisture measurements are very site-specific, so develop a history of soil moisture and use it to determine when the best time is to pull the irrigation trigger.
· Monitor shoot tips (see photos).
o As long as shoots are actively growing (first photo on left), there is no need to irrigate, unless shoots are stunted.
o Irrigation may be necessary when shoots are slowing down (second photo from left) and need to gain more length before stopping.
o Irrigation may be initiated when shoot growth ceases (approaches the third photo from the left).
· The pressure chamber apparatus may be used as an adjunct to shoot tip evaluation. Generally, shoots stop growing when midday leaf water potential reaches -10 to -11 bars on a mild weather day.
· Some parts of any vineyard will show signs of irrigation need sooner than the rest. If possible, irrigate those vines with separate, dedicated, drip hoses, before initiating irrigation for the rest of the block.
· A short irrigation for fertilizer application does not necessitate continued irrigation cycles.
· Once irrigation is started, apply only the amount of water required to wet the effective root zone. In our climate, we cannot truly “drive” the roots down deeper with drip irrigation. In most north coast vineyards, application of more than 3 or 4 gallons per vine per irrigation pushes water below the root zone. Such water is wasted.
Prepared by Mark Greenspan, Advanced Viticulture, with input from Sonoma County winegrape growers
Active Shoot Growth Slowing Growth Stopped Growth Dead Shoot Tip