Skip to main content

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.

Comments

Popular posts from this blog

Downy mildew gallery

At Winchester, we had light rain events during the night of 6/12/09, but it was short events and the relative humidity was low (80% or so), thus it probably did not promote any infections. However, we are experiencing continuing favorable nights for downy mildew sporulation (average T>55F, high RH (80-100%)) for 10 days now. Yesterday, we conducted a formal disease assessment, and observed first incidence of powdery mildew for this season. We had plenty of infection events in last two months, so it was not surprising. At this point, it is a trace level of infection on untreated vines. Downy mildew was the major disease so far. We had up to 40% incidence on untreated vines. Next runner-up was black rot. It varies vine to vine, but some of vine had 10-15% incidence. Phomopsis was omnipresent as I expected from early May rain falls, but severity was low overall. We will examine diseases again in the near future, and I will update as the season goes. Here is downy mildew ga

Season's Greetings!

I hope you and your family have a good holiday season and a Happy (and safe) New Year! Thanks again for your support of our programs. Here are some recent media highlights. 😉 The link will open a new window. AHS AREC promotional video  that highlights some of our activities. The link did not work... It asks you to log in to VT. I will request the IT people to change the setting, but in a meantime, here's the same video. We also appeared in  the Library of Congress project “Winery Workers of Virginia”. One more announcement: I will be moving this blog to a new location ( ext.grapepathology.org ) early next year. I had to make a change due to the email subscription service, which has been terminated.  You do not need to change your bookmark or your email subscription. The URL will be forwarded to a new site and your email subscription has been moved to a new site already. 

Recent downy mildew risk events

 It seems that several rain events have happened over the course of the past two weeks or so. Here is a summary of recent downy mildew risk events, based on the NEWA stations and DMCast. Bristol, VA Fifteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Floyd, VA Eleven days with potential DM infection event(s) since Sept 1. The last event happened last Friday. Charles City, VA Twelve days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Central VA Since there was a wide variation among stations, I am listing several around Central VA. Tyro, VA Nine days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Red Hill and Crozet, VA Only one day with potential DM infection event(s) since Sept 1. Olympic Lake Thirteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Washington, VA Eight days with potential DM infection event