Yield prospects for Sonoma County vineyard hinge on type of pruning system

Yield prospects for Sonoma County vineyard hinge on type of pruning system

The wide swings in weather conditions this year highlight the impact of different pruning practices on how his vines have responded so far this season.

Sonoma County wine grape grower Mark Hauser looks back on the first half of this year as six months of whacky weather.

For starters, winter and early spring rains returned to the southern end of the Alexander Valley where he manages a total of 320 acres of grapes for Hoot Owl Creek Vineyards and Alexander Valley Vineyard’s. More than 24 inches of rain fell on his vines from January through April, filling rivers and reservoirs to levels not seen in at least four years.

His fields even received a quarter-inch of precipitation in an uncommon mid-June rain event.  And, unlike some years when his vines have experienced as many as a dozen days of freezing temperatures, this year, frost protection was required just once. That was in late March in a few blocks of white grapes

At the same time, temperatures have varied from normal or below to unseasonably warm, if not downright hot. For example, in March and April, his thermometer registered several days of temperatures in the high 80s .Alternating periods of warmer and cooler weather, accelerated and then slowed vine and fruit development for much of the spring. Capping it all off was a l00-degree heat wave the last week of June.

“The weather has been schizophrenic,” Houser says. “Hot or cold and wet or dry. But, that’s farming and you deal with it.”

He’s been doing that at both vineyard operations for the past 17 years. The Alexander Valley AVA is known for its Cabernet Sauvignon, and that’s his main variety. He and his crews also grow such varieties as Cabernet Franc, Chardonnay, Merlot and Zinfandel along with some smaller blocks of Petite Verdot and Malbec for blending.

The wide swings in weather conditions this year highlight the impact of different pruning practices on how his vines have responded so far this season.

On his cordon spur-pruned vines, where the two buds left on each of six or seven spurs on the arm of the vine tend to flower at about the same time, the fruit didn’t set very well this year. Houser estimates their yields will range from a little below to a little above average this season.

In fact, in one seven-acre field of cordon spur-pruned vines of Cabernet Sauvignon, growing on medium-vigor rootstock, cluster development was stunted by rain or heat just as many of the buds were flowering

“Even though it’s just a minor part of our whole operation, we lost 40 percent of the fruit in that particular block,” he says.

On his cane-pruned vines two to four canes on the vine are pruned to leave anywhere from six or seven to about 15 buds per cane. Since buds near the end of the canes flower later than those closest to the vine, adverse weather that affects some buds may not affect others.

“Where blooming  buds were exposed to heat or rain early in the season, the cluster set is off anywhere from 10 to 30 percent,” Houser says. “However, where buds were protected by the canopy it looks like a tremendous crop. But, it’s still early in the horse race. We’ll see how the berries size at veraison.” 

That’s when he’ll decide which clusters he’ll remove, as needed, to meet his yield and quality goals.

“I want to get a good idea of likely crop size before touching anything,” he says. ”I hate to pull any fruit only to wish later that I could put it back on the shoot.”

Depending on variety, Houser’s vines began blooming from April 25th to May 20th. As a result, he expects veraison will begin around July 10-15 with his Chardonnay. That would have these grapes ready for picking during the last week of August.

Once the clusters color, his crews will begin selectively thinning them. That includes removing any affected by measles or Pierces Disease, clusters on short shoots and second crop as well as those clusters that may have Botrytis strikes from the rain in June.

“Even though the summer heat will dry up these infections, the Botrytis inoculum remains in the clusters,” Houser says. “If we get rain close to harvest, that Botrytis would take off like wildfire.”

He’ll also remove clusters from vines that are stacked or matted. These vines have three or four clusters piled on top of each other, restricting the air flow needed to minimize the threat of powdery mildew and botrytis, he notes. Here, the goal is to thin the clusters so they hang level without overlapping.

Powdery mildew pressure tends to be highest in his Chardonnay with its much thinner skin than his red varieties. Controlling that threat includes removing leaves to allow better flow of drying air around the clusters and to improve coverage when dusting his vines with sulfur or spraying fungicide treatments.

Prompted by increasing concerns about the continued availability of labor to open up these canopies. Houser took delivery of a new German-made leaf-plucking machine in early June.

We use it on the morning side of our north-south rows to expose about 85 percent of the fruit to air and sunlight to reduce the risk of powdery mildew or bunch rot and to improve coverage of fungicide and pesticide applications,” he says.

 Typically, his two main insect pest concerns are leafhoppers and mites. However, this year, up until the first of July, Houser reports that he as well as other growers in the area had seen few, if any, leafhoppers.

“Of course, we may still have to treat for them and mites later this season,” he says. “Here in our vineyards we grow a cover crop of buckwheat as an insectary. I’ve seen a tremendous amount of beneficial bugs this year. I don’t know if that’s helping to keep the number of bad bugs down, because no one has been seeing many of them so far.”

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