With crews beginning to pick Pinot Noir and other early wine grape varieties in early September, San Luis Obispo growers will soon learn the full impact of the widespread April freeze and the success of their efforts to limit the damage.
Sub-freezing early April cold descended over this and other areas of California’s Central Coast region. Among the San Luis Obispo vineyards hit hardest by the frost were those in Paso Robles and surrounding areas. Those in the coastal areas generally suffered less, says Mark Battany, University of California Cooperative Extension Viticulture Farm Advisor for San Luis Obispo and Santa Barbara counties.
“Inland vineyards with sprinkler frost protection fared well, provided they had sufficient water to cover the extended cold period,” he says. “Wind machines were less effective, due to exceedingly cold temperatures and weak temperature inversion conditions.
“It will be difficult to assess the effect on production until the numbers are reported, but there is a huge variation from site to site. Vineyards which were protected successfully with sprinkler frost protection appear to have relatively good yields. However, vineyards in heavily affected locations have certainly seen production reduced by half, or in some cases much more. And, grape quality will be compromised at many sites due to the large variations in fruit ripening.”
Growers in areas lightly affected by frost saw only partial damage to emerged primary shoots, Battany notes. In other areas, all primaries were frozen and the vines responded with growth of secondary and latent buds. Latent buds tend to be less fruitful than primaries, reducing yield potential.
Many growers were reluctant to remove damaged shoots immediately after the early April freeze. That would have left them vulnerable to the continuing threat of frost through the end of the month and subsequent heavy losses, Battany explains. Many growers thinned shoots by late spring to reduce crowded canopies, improving the fruiting zone microclimate and encouraging proper bud initiation for next season’s crop. Others thinned fruit later to help even out the ripening of the grapes — an important consideration with machine-harvested blocks.
Weather conditions during bloom were erratic, reducing the set in many inland and coastal areas. Cool temperatures led to high powdery mildew pressure, also encouraging growers to thin canopies.
The San Luis Obispo harvest now hinges on the weather this month and next. By early September warm temperatures had returned.
“Moderately warm, sunny and dry conditions through October would be appreciated,” Battany says. “Sustained warm weather will speed ripening. But, excessively cool conditions, like last year, will delay harvest and may lead to potential losses due to early fall frosts and rains. We're hoping Mother Nature doesn't throw us any more curve balls this season.”