Wednesday, July 22, 2009

More rains in the forecast

Rain on this Monday did not last long, but since it started later in the day, the relative humidity was high (>90%) until next morning. Thus, we had >15 hours of wetness event with an average temperature of 68F or so. This accounts for infection event for Phomopsis, downy mildew, black rot, and Botrytis, and ascospore discharge for powdery mildew. And I'm aware that areas in the south of us received more rain last night. Please check your local weather record.

In addition, we are having five consecutive nights with high relative humidity that favors downy mildew sporulation. If you have issues with downy mildew this year, you may need to take some action before or after next round of rain. (but again, it depends on growth stage of your berries. If it is past 4-5 weeks after bloom, the risk of downy mildew infection on berries is very low.)

Unfortunately, there is no curative fungicide for Botrytis, thus you need to protect your berries against infection. As I mentioned in the previous post, often time, protection at berry touch and at veraison is recommended. Please refer to either my spray guide or VT's PMG for list of fungicide you can use.

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