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40 WINES&VINES May 2017 GROUNDED GRAPEGROWING tion may be required for summer weeds. Applying herbicide later makes sense in higher rainfall years, but timing can be difficult. Ideally sprays should be made be- fore the overwintering weeds bolt so that there is not a lot of dead plant residue beneath the vines. Best timing for these sprays would be late January or early February. Canopy management and fungal disease In general, high soil moisture early in the season will cause abundant vegetative growth. This can affect crop set during the current season and the next season if there is dense foliage around the flowers and clusters. Shading affects the next season's crop when buds are differentiating on the basal buds of the new green shoots. Pre-bloom canopy management helps lessen this problem. Do it early if you can! Thinning sterile shoots on trunks and cordons will help. Tuck shoots when they are relatively short; cane damage is much more likely to happen with large shoots. Pulling leaves around the shoots at flowering time can help set a smaller crop if it appears that large flowers are likely to form large clusters. (This can be risky: If the weather gets wet, you are likely to have a poor set anyway, so don't do this unless you are sure bloom weather is going to be good. Wait until the last possible practical time to get the job done.) Similarly, if there is a lot of shoot growth and you are worrying about poor fruit set due to shatter, tipping the vines prior to bloom may help set a bet- ter crop. It will also cause lateral buds to break, making canopy- management more difficult due to lateral shoots. Mechanical hedging is the best way to maintain a can- opy that starts to get out of control. You may need multiple passes in a year like this. Powdery mildew tends to be a problem following a wet year as often spring weather conditions fall into the ideal temperatures for disease: 70° to 85° F. High hu- midity may also exacerbate fun- gal problems. The foundation of a strong pow- dery mildew program is early sea- son sprays with wettable sulfur or Stylet oil when vines have 3 to 6 inches of growth. This controls the overwintering form of the disease and the first infections. When done properly, it may represent 95% of a control program according to the UC Grape Pest Management book (UCANR Press Publication 3343). Follow-up applications can be made every 6 inches of growth or 14 days. If you are alternating be- tween the two materials, wait at least three weeks, as phytotoxicity is likely when used too closely to- gether. Never mix these materials together! Pulling leaves after fruit set is also going to help reduce mildew in developing clusters, as lower humidity and sunlight exposure lessen disease development. Also, fungicides can reach the fruit with better coverage and more effective powdery mildew control. Botrytis shoot tip and bunch rots often are a problem. Normally it isn't very practical to spray for shoot tip rot control. It happens when conditions are very wet, so getting spray rigs into the vineyard isn't easy. Vines aren't seriously af- fected in most cases, but there will be more lateral shoot growth. You may also start a source of inoculum that will cause further infections if rains continue. Botrytis bunch rot can be a problem, with early infec- tions happening at bloom. If you have had bunch rot problems in the past, consider a fungicide pro- gram that would include sprays during bloom and again before bunch closure. There are fungi- cides registered for bunch rot con- trol for both conventional and organic/Biodynamic growing sys- tems. If you are growing varieties with large berries and/or tight clusters, you might want to use fungicides as odds are cluster weights and berry sizes will be larger than usual, predisposing fruit to Botrytis infections. Leaf removal around the clusters after bloom will also be important. Insects and mites If weather is cool following bud break, shoots tend to grow slowly. Willamette mites and western flower thrips can become a prob- lem, as they are feeding on the lim- ited amount of green tissue that concentrates injury. Stylet oil can be used as both a fungicide and insec- Custom made - Handcrafted Barrels