Vines Still Happy, But Slightly Stressed

Farmers debate how much water stress vines can handle before irrigating

“Things are moving fast out there!” reports viticulturist Kevin Skene from Sonoma. Warm weather continues this week in all areas “shortening the window to get passes in” according to Matt Hardin of Barbour Vineyards in Napa Valley. “The conditions are warm, tracking perfectly, and are shaping up to be as great as 2008,” says John Conover, the General Manager of PlumpJack Winery in Oakville and a member of the Napa Valley Grapegrowers. “If the adage of 120 days to harvest holds true, we should be looking at harvesting in the middle of October.”

The Great Leafing of 2012 continues, thanks to those jungle-like conditions we reported on last week. Over at Mill Creek Vineyards & Winery in Dry Creek Valley, Winemaker Jeremy Kreck reports that his crews “have just finished removing leaves near the fruit zone to allow both sunlight and air exposure to the developing clusters. The air circulation helps reduce the mildew pressure and the sunlight is instrumental in reducing green bell-pepper aromas in the finished wine.”

While Skene’s crews are likewise “mostly finished pulling leaves and laterals from the fruit zone to get that ‘dappled light’ effect which is key for ripening,” they are continuing to “get rid of excess growth and balance the canopies.” Hardin’s crews “are removing laterals, typically on the morning side” and are also removing fruit on weak canes. Although, “no real fruit thinning will be done until closer to veraison.”

Speaking of fruit, how are the grapes themselves looking? “Berry growth continues and for most blocks we are over 50 percent of expected berry size,” says Kreck. Skene is seeing bunches beginning to tighten and close in the Russian River Valley, Dry Creek Valley and Alexander Valley.

Which means it is also time to spray. Terri Harvey, a manager of one of the oldest zinfandel vineyards in Amador County is rushing to get her fungacide sprayed before the bunches close in order to prevent powdery mildew and bunch rot. She is also spraying miticide, because once those eggs hatch, the nasty little critters suck chlorophyll out of the leaves. And you can imagine that 140-year-old vines need all the energy they can get.

Kreck hasn’t had trouble with pests yet, but their “spray program for powdery mildew continues with an organic stylet oil on 7 to 10 day intervals.” Hardin is also starting to see mildew “here and there.” He blames the ideal temperatures and healthy vines which have led to congested canopies. Proving that farmers just can’t win.

As the vines begin to slow down in vigor and ultimately stop growing, the big question on every grape farmers mind is when to irrigate. “How long can we wait before we start?” asks Hardin.

Skene has started to irrigate some hillside blocks that have “shallower soils and are drying out faster.” At Mill Creek, Kreck has begun monitoring his vines for water stress by using a pressure bomb: a device that measures the pressure needed to extract water from the leaves of a vine. “The more pressure needed, the lower the water content,” explains Kreck. “We have not gotten to a point where irrigation is necessary as there is still a sufficient natural supply of water in the soil.”

Greg La Follette takes an old-fashioned approach to testing his vines for water stress: “For me the most important indicator of vine water stress is a device called a vine — not neutron probes or gypsum blocks or pressure bombs. Look at a vine and see everything it is doing and it will tell you what it needs.” La Follette believes that watering too soon is one of the biggest mistakes farmers make. “They see a little bit of cansado and they go in and water. But that is the wrong thing to do.”

“If the leaves are looking perky in the morning, tracking the sun all day and by the afternoon they are tired, you have to check them again the next morning. If they are perky again that means they have recovered overnight and you don’t need to water.” But, says La Follette “if you start seeing lack of solar tracking and laminar folding then you know you should be watering like now, like immediately.”