I received comments from Anton on the previous post about Botrytis.  He is more concerned about Rovral (=Meteor), Vangard, and Scala than I indicated.

I wasn’t very clear on the previous post about how the information has been developed.  There are two components in this story.  One is the probability of having Botrytis with resistance to some of the Botrytis materials.  So far, it seems that probability is very high for Flint (or other QoIs), high for Endura and Pristine, moderate for Rovral (=Meteor), and unknown for Vangard and Scala.  The other component is the level of resistance.  It is high for Flint, moderate to high for Endura, and Pristine, moderate for Vangard and Scala, and low for Rovral. 

The key point that Anton helped me understand today is that even though the resistance level against Rovral is “low”, it still means that the labeled rate won’t be as effective as it should be.  Thus, if there is a certain percentage of Botrytis which has low resistance to Rovral, it may result in less than optimal control of the disease.  (Note: this is based on on-going research, as Anton obtain more samples, we will get a clearer picture.)

The question is what to do.  I think the bottom line is to make sure you have a good cultural practice to lower the risk of disease outbreak.  Whether the isolate you have in your vineyard is resistant or not, if the infection conditions were not met, it cannot cause disease.  Also, make sure to rotate the mode of action.  When you rely on one mode of action, you are helping development of a resistant isolate.  Scouting is important as well.  If you see any signs of failure of spray material, please contact either Anton or me.  Anton has a very simple sampling kit for Botrytis.  Another important piece of the puzzle is your sprayer.  Make sure to maintain and calibrate your sprayer so that you can have a good consistent coverage of fungicides.