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Initial infection event for powdery mildew

Well, it typically won't happen until May or so, but under this weather conditions, you cannot expect the usual trend.  Often time, powdery mildew is common under dry weather because powdery mildew conidia, which are primary spores during summer time, do not require water for infection.  However, ascospores, which are initial inoculums (spores), require water.  More than 1 inch of rain followed by 13 hours of leaf wetness with an average temperature range of 50-80F is required for powdery mildew ascospore infection.  Winchester area received rain starting from 9:15am today, we are having pretty much continuous rain (and it's still going), and the average temperature (at this point) is about 60F; therefore, it counts as an infection event.

If your vines already broke buds, the new growth are susceptible for infection.  Please monitor leaves for powdery mildew to see if it was indeed an infection event for you.  It typically takes about 7-10 days for disease development.
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Comments

  1. Anton BaudoinMarch 25, 2012 at 9:18 AM

    I wonder if we might have the potential for powdery mildew "flag shoots" in some parts of the state, due to the mild winter we've had.

    ReplyDelete
  2. Mizuho NitaMarch 25, 2012 at 10:05 AM

    Thanks, Anton! Yes, this would be the year to have flag shoots. I posted a new article to cover it.

    ReplyDelete

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