Disease risks from today’s rain and a little bit about Botrytis

There are still a chance of an afternoon rain, but here are estimated disease risks from rains from yesterday to this morning.  We had about 16 hours of an estimated leaf wetness period with an average temperature of 63F.  It was infection events for Phomopsis, black rot, and downy mildew. 

I think most of us are getting close to or at bloom.  Please remember that a period between bloom to 4-5 weeks after bloom is a critical time for fruit infection by powdery mildew, downy mildew, and black rot.  Also, at bloom, we recommend protection spray against Botrytis because it can infect flower parts and either resides in it or stay with flower debris until later in the season.

Many of you probably remember a report from Dr. Anton Baudoin about fungicide resistance of Botrytis pathogen, Botrytis cinerea.  This pathogen can infect wide variety of hosts and it is known to develop resistance to a fungicide or multiple fungicides relatively quickly.  Thus, Anton is investigating what is happening with Botrytis found on grapes.  He shared his preliminary findings with the Viticulture note earlier this year.

Here’s a synopsis: So far, Elevate, Switch, and Rovral (Meteor) are Good, Scala and Vanguard are OK, Endura, Pristine, Flint are in question (i.e., it may no longer provide an adequate control, if you have resistant isolates).  As far as I know, Luna Experience provides a good protection, and the same will go with Inspire super; however, Botrytis component of these two products are in the same group as Endura (boscalid) and Vanguard, respectively, so, it is possible that Botrytis will figure the way out, especially for Luna.  Luna’s SDHI component (fluopyram) is different from boscalid, but they are under the same FRAC code (= the same mode of action).  Whether boscalid resistance isolates are resistance against fluopyram or not is still unknown.   Their partner material is a DMI for both Luna and Inspire, but DMI does not provide much protection against Botrytis.

Luckily, Elevate (FRAC 17), Switch (FRAC 9+12), Rovral (=Meteor FRAC 2), and Scala and Vanguard (both are FRAC 9) are in different mode of action groups.  Thus, you can rotate them around.

Also, please keep in your mind that cultural practice can provide many benefits to Botytis management.  A good air circulation within canopy to promote quick drying time and lower relative humidity really works.  Plus, prevention of wounding events (by birds, grape berry moth, etc) is also important.

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