Vineyard conditions this year have been much wetter than average, bringing more risk of disease. Technical Services Manager for UPL North America, Cassie Rieser said infections can occur during bloom through the stigma of the flower. The infections can lay dormant until sugar content in the berries increases.
“Prolonged periods of warm and moist conditions, and especially susceptible winegrape varieties like zinfandel, paired with elevated nitrogen levels and dense canopies, can promote botrytis outbreaks,” Rieser explained. “Late season infections become more severe when that relative humidity exceeds 92 percent, and when free moisture is present on the fruit surfaces and temperatures are anywhere from 58 to 82 degrees. Then grapes in a condensed cluster can end up cracking due to pressure against each other later in the season, it can create an ideal entry point and promote the spread of botrytis.”
The increased moisture can also contribute to increased plant vigor, promoting canopy development. Cultural control will play a significant role in keeping botrytis outbreaks from damaging vineyards. Maintaining an open canopy and removing leaves from the fruit zone helps with airflow and reduces risk of disease development. Rieser said there are also a number of materials to support cultural control approaches.
“PH-D is one of our trusted fungicide offerings and it offers effective control. It has a unique mode of action that becomes a really important resistance management tool for tough diseases in grapes. It is the only product in FRAC Group 19, which again makes it a great tank mix partner with other fungicides,” said Rieser. “The benefit of PH-D is that it does have a zero-day preharvest interval and a four-hour reentry interval making it a really great option for disease management sprays especially closer to harvest.”
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