Agronomic Minute: Wet Weather Creates Ideal Conditions for Grape Diseases

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California started 2022 off with much-needed rain events, which could ultimately lead to higher levels of grape diseases. UPL Technical Service Manager, Emily Smith explained that last year’s dry conditions were helpful in limiting disease damage in vineyards. Growers will want to be mindful that moisture levels are much higher this year and more action may be required than in 2021.

Grape Diseases

“If this weather continues on through the rest of the winter and maybe into the early spring, there will be some more diseases,” said Smith. “This year I think we might see some botrytis. Botrytis is a big one for grapes and sometimes you can have spring botrytis, which can cause flower blight during bloom which would affect the clusters eventually. It could also affect the shoots and the shoots could break. So, that can be an issue right off the bat.”

Phomopsis cane and leafspot can also be a problem for growers, as well as powdery mildew. Depending on the weather moving into February and March, Smith noted that pruning wound diseases could be problematic if California receives more rainfall after pruning. Getting preventative materials applied early on is recommended to help get ahead of any disease pressure that may be building. “As soon as there is green tissue, you want to go out with these preventative fungicides, or some of the systemic fungicides, or PH-D, which is also a very helpful knockdown. Keep your intervals to maybe 10-14 days if pressure is really high,” said Smith.

Spray programs will generally begin sometime between February and March with bud break timing varying across California. Smith noted two to three inches of growth in the shoots as being good timing for preventative fungicides and potentially a contact material to combat grape diseases.

“Oil and copper tend to go on early on,” said Smith. “Sometimes growers go with lime sulfur in the dormant season to knock out any sort of pressure that’s already building.”

Listen to the full episode below.