Powdery Mildew Control: March through Verasion

In our area, powdery mildew is the primary annual threat to our crops. We have included three methods for controlling this pest. Make sure the spray covers all leaf and cluster surfaces, and be careful not to vary these schedules. Even the smallest deviation from these steps can result in powdery mildew destroying your crop.

• Method 1. Apply wettable sulfur when shoots first appear. Reapply every seven to ten days until verasion, when red grapes turn red or white grapes reach 12 brix. Reapply immediately if sulfur is washed off by rain.

• Method 2. Apply wettable sulfur when shoots first appear. Reapply every seven to ten days until shoots are 12 inches long, then switch to Rally, a sterol-inhibiting fungicide. Reapply immediately if washed off by rain. Apply Rally at four ounces per acre on a 21-day spray interval until verasion.

• Method 3. Apply JMS Stylet-Oil (parafinic oil) every 14 days. JMS is an eradicant, so it will not only prevent, but also kill, powdery mildew colonies. Do not use more than twice on ripening grapes.

Fertilizing/Irrigation: March through October

Vines should be fertilized and watered as needed to sustain growth and provide optimal fruit. The goal is to grow vines that are in balance. A balanced vine is defined as one with 36-inch shoots, at least 15 leaves per shoot, and no more than two grape bunches per shoot. Some of our vineyards are dry-farmed (no fertilizer or water) to achieve balanced growth, while others receive fertilizer and water. Young vineyards (those that are no more than three years old) should receive both fertilizer and water.

Irrigation

Drip irrigate every two weeks for four hours per session as needed. Begin irrigation two weeks after the last heavy rain. Decrease watering after berries set, and further reduce watering by September when red grapes turn red (verasion). If climate grows particularly hot (in excess of 100 degrees), it may be necessary to water to keep the grapes alive and robust. Water deeply 12 to 24 hours one time as soon as grapes are harvested.

Fertilizing

For vine balance, apply 16-16-16 fertilizer every six weeks at a rate of ½ cup per vine or ¼ cup per emitter while drip irrigation is in progress. Stop fertilization in late summer. Apply 16-16-16 fertilizer one time as soon as grapes are harvested to promote strong root growth during winter months.