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Favorable Weather Aids Start of San Joaquin County Wine Grape Crop


The growing season for this year’s San Joaquin County wine growers began early in the first week of March as buds on Chardonnay vines began to open. That trailed last year’s start by several days. Still, it was 10 days earlier than the long-term average start of bud break, says Paul Verdegaal, the county’s University of California Cooperative Extension farm advisor for viticulture.

For the first time in a quite a while, the vines received quite a bit of chilling this past winter prior to bud break, which typically occurs from March 13 to 15 in San Joaquin county. “Grape vines don’t require nearly the same degree of winter chill as other fruit crops.” Verdegaal says. “But, because of good chilling early in the winter, the vines were ready to start growing as temperatures warmed up enough.

“In fact, the weather in February was unusually mild. Plus, a very wet December, a fairly wet January and a wet March provided good soil moisture to start the season.”

Typical annual rainfall in the county from October to May totals close to 17 inches, Verdegaal reports. Last year, the country received about 13 inches of rainfall during that period.

In 2012, the first year of the current drought, vineyards here received a little over 12 inches. The following year, rainfall totaled almost 16 inches, about 94 percent of normal. “Many people have tended to have forgotten or glossed over that break in the drought,” Verdegaal says.

The 2014 season was the driest of the past four years with rainfall totaling only around 10 inches or so. That was followed in late fall and early winter by temperatures cold enough to hurt both young vines and old vines, even killing off some old Zinfandel vines. “So, although not a drought buster, 2016 is on track to be a “normal” with regard to rainfall.” he adds.

The primary disease threat to San Joaquin County vineyards this spring, as usual, is powdery mildew, Verdegaal says. In fact, by the first of April it already was a concern in some blocks of early Chardonnay. Wet ground, particularly in the lower foothills, in the Delta and sites on heavier soils delayed or complicated efforts of some growers in applying sprays to control the fungal disease.

Despite earlier concerns the El Nino weather pattern might lead to more botrytis shoot blight this spring and possibly Phomopsis cane and leaf spot, these fungal diseases haven’t posed much of problem for growers so far, he notes.

In 2015, dry weather in January and February contributed to unusually heavy pressure in the vineyards from vine mealybugs. However, the cold temperatures last fall and early this past winter along with the wet weather seem to have kept populations of this pest in check. “No one seems to be concerned about early vine mealybugs this year,” Verdegaal says. “However, conditions have been wet enough that snails have popped up in some vineyards, as can happen in cool, wet years.”

Meanwhile, growers aren’t sure how their current disease, pest and nutrient management programs might be affected by the various new or pending regulatory monitoring and reporting requirements concerning labor rates, worker safety and ground water quality.

“The added costs of complying with these new regulations are especially burdensome on smaller growers who may have to hire people with the expertise to help them with the process,” Verdegaal says.

Source: Greg Northcutt, Western Farm Press

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