One of the Worst Powdery Mildew Years in Recent Memory

Brian German Grapes, Industry, Nuts & Grapes

Grape growers had a challenging season dealing with powdery mildew issues. BASF Technical Service Representative, Kevin Caffrey said it was one of the worst years in recent history. A major factor was a significant amount of moisture at inopportune times in the season. Another complication was that many growers did not start the season with a strenuous management program.

Powdery Mildew

“Part of that was because the last few years they got away with it. They could have some lighter early programs and still control the pest. That was not the case this year,” Caffrey noted. “And once you get powdery mildew, it’s not easy to eradicate it.”

Growers that started the season with strong mitigation programs fared much better than those that did not. Powdery mildew problems can exacerbate issues with bunch rot. Unseasonable weather in July created further challenges with many areas receiving rain right as veraison was underway. “In 48 hours after that rain, you had the strong smell of vinegar from all the sour bunch rot. Some were full losses,” Caffrey explained.

Table grapes were hit especially hard by the inclement weather during the season. At the same time, Caffrey said that winegrape growers were dealing with similar issues with powdery mildew, followed by bunch rot. Rain in July was also a problem for raisin grapes. “If they were still on the vine, those tight clusters, especially Thompson seedless, they were just covered in bunch rot. You could smell it from a mile away,” said Caffrey.

Growers are encouraged to consider a more robust management program heading into the next season. Vineyards will have a significant amount of inoculum and forecasts are calling for another wet winter. Starting with a strong program and evaluating the conditions as the season goes on could be necessary to avoid losses experienced this year.

“I think if people start strong and have a good plan, then you can pivot from there and decide,” Caffrey noted. “I think they have to plan to go strong because a lot of people lost more than they expected from all the different weather events.”

Brian German
Ag News Director / AgNet West