LAKE COUNTY – Speeding by row after row of verdant grape vines, you might not realize that Lake County vineyards are on a water diet that keeps them healthy but slim.

While many other crops are grown for maximum yield with lots of fertilizer and water, the best quality winegrapes are grown with an open canopy that allows dappled sunlight to reach the fruit.

Too much water will grow monster vines that produce vegetative flavors. Canned green bean is not what the winemakers want! Too little water can also harm fruit causing shrivel, sunburn and raisin flavors.

The approach of giving vines enough water for an open and balanced canopy is called deficit irrigation, implying that vines are grown with less than full water availability.

As a matter of fact, winegrapes in Lake County use a lot less water than other crops. While vineyards get by with 5 to 10 inches of applied water each year, irrigated orchards, hay and pasture use 20 to 40 inches.

Deficit irrigation requires careful monitoring of soil and vine water status. Devices with names like soil tensiometers, neutron probes, and dielectric water content sensors are used to measure soil water availability.

Vine water status is measured with instruments such as pressure chambers and the phytogram. Growers also use systematic observations of shoot growth rate and shoot tip vigor to help decide when water availability is limiting vine growth.

Almost all Lake County winegrape growers have micro-irrigation or “drip irrigation” systems. With these systems each vine has one or two emitters that drip water out at a specific rate.

These systems are very efficient because they allow for careful regulation of the amount of water applied, and they create only a small area of wet soil from which water evaporates.

Lake County is fortunate to be one of the few regions in California with a publicly available network of weather stations.

The Lake County Pear and Grape network is a cooperative effort among UC IPM, UC Cooperative Extension, the Lake County Air Quality Management District, the Lake County Department of Agriculture, the Lake County Winegrape Commission (LCWC), and three growers who have purchased their own stations.

Winegrape growers use information from the station nearest their vineyard to guide water applications. Measurements of temperature and humidity are fed into a formula that calculates how much water vines are using, and growers access this information on the website. Using local and up-to-date weather information, growers can fine tune their irrigation program.

In the Vineyard is a monthly feature from the Lake County Winegrape Commission. For information about Lake County’s winegrape industry and the Commission, visit the commission’s Web site, www.lakecountywinegrape.org .