Driving around Kern County, I see many vineyards with spurs growing out the top that look like hair on‐an‐angry‐dog’s back. In addition to all the spurs, there seems to be two to four long or short extra canes, as if this is not enough wood already.
This concept for increasing crop production can hit a point of diminishing returns. Lower cluster counts, equal more wood, equal more shoots, equal more shade and less clusters, a vicious crop cycle. Research has shown that shoots need light penetration for cluster primodia initiation. This procedure can also lead to over‐cropping and delayed bud break in the spring. There seems to be more delayed bud break in 2012.
(For more, see: California wine grape supply on cusp of shortage)
All the extra foliage means more shade and more difficulty in achieving good spray coverage for powdery mildew (PM) control. Extra foliage can be reduced by removing shoots that do not have clusters at an additional cost. All the extra foliage has to be protected from powdery mildew infections, not just the cluster area. Equipment adjustment is a key factor in good coverage. In addition to the spray program, a good sulfur duster is a key ingredient to the overall powdery mildew program. Sulfur will coat all the foliage and after bunch closing can penetrate tight clusters and protect the stems. The use of sulfur will require more scheduling for the workers but the improved coverage and protection is well worth it. I know of growers that tried total spray programs but added sulfur back into the mix.
What to do if powdery mildew becomes a problem
A general emergency procedure is to do a wash job. A wash job consists of insuring that all foliage is wet and a large canopy can require 900‐1000 gallons of water per acre; 200‐300 gallons per acre will not do it. Control is through contact of water and the PM and the spray usually consists of water, a wetting agent and a low rate of micronized sulfur. This spray will only protect for two to three days and a follow‐up program with a fungicide spray or sulfur dusting will be needed.
Last season, several growers that I talked to all agreed that Autumn King had light to severe PM problems and increased rot. In vineyards that I observed there was heavy and dense foliage. This combined with large berries and tight clusters is a recipe for problems.
What to do? Space the clusters to improve spray coverage, remove some laterals to help loosen the cluster (a tight cluster that rots is of no use) monitor thrips populations and control if necessary to reduce berry scaring and points of entry for decay organisms. Consider using additional sulfur dustings if temperatures are favorable and rotate fungicide sprays with sulfur dusting. Adjust all equipment so that 100 percent of the canopy is covered and protected, and last but not least, remember to rotate all fungicides as per the manufacturers’ instructions.