Thursday, April 19, 2012

Disease risks from yesterday's rain

Winchester area received a series of rain events from 5:30AM on 18 April.  It lasted about 10 PM.  Since the rain stopped at night, leaf wetness is still on-going (i.e., RH > 90%) as of now (~9AM, makes it 27.5h of estimated leaf wetness), and the average temperature is about 49F.  Thus, it has been an infection event for Phomopsis and black rot. 


  1. Whats the best thing to spray at this point if you haven't done your first spray yet. Should you still go with Mancozeb?

    1. Since none of the materials we have have activity after the infection on Phomopsis, it is probably better to go with mancozeb products.

      We had a several rain events that are warm enough for black rot, thus I will keep eye on black rot development too. It typically take about 2-3 weeks for black rot to develop symptoms. Once you start seeing black rot, and if you are expecting (or experienced) a warm rain event, then I would recommend to add a DMI to your schedule.

      Note: it is probably not worth adding a DMI at this point because in typical year, black rot appears later in the season, exception is the case where you had an outbreak of black rot last year, and know that there are many inoculum available. Even with that, adding a DMI at this early in the season make your season-long spray program (i.e., rotation of mode of action) more difficult. Thus, I would proceed with caution.


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