With grape harvest in CA underway, it’s important to know some of the disease pressures your crop may be facing. Diseases like botrytis and powdery mildew can impact yield and overwinter in fields, remaining a persistent issue for years to come. To get some answers on what to look out for, we brought our agronomist Garrett Gilcrease to this year’s CAPCA Conference, where he offered insight into the 2018 growing season.

What grape varieties are most prone to disease pressure?

Really most of them, with a few that are somewhat immune; such as Ruby Red and Concord. Varieties like Zinfandel, Carignan, Autumn King, Scarlet Royal are all very susceptible to both botrytis and powdery mildew. Mildew being the most prevalent, with botrytis coming on when conditions are correct.

How do you spot powdery mildew and botrytis?

Mildew is easy to spot, with white, fuzzy coverings on leaves, clusters, stems and petioles. Botrytis begins with the grapes obtaining the smell and coloring of brown, rotting berries, and then is followed by grey or white masses of the botrytis.

How do they impact grape harvests?

Mildew has a strong impact on yield, as the mildew limits photosynthetic production, thus limiting canopy size, cluster size and brix generation.

In CA, we’re testing new fungicides that show promising opportunities for grape growers against powdery mildew and botyrtis. We anticipate registration of Aprovia® Top and Miravis® Prime fungicides for grapes in the next few years. Aprovia Top will have a fit for early-season control of powdery mildew, while Miravis Prime will provide later season powdery mildew and Botrytis control. Both fungicides are showing bigger and cleaner fruit, compared to competitor products and untreated grapes.

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