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

China Agriculture Report By CnAgriChina Agriculture Report Print

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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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