Bloom time disease management considerations

Many of our vines at VT's AHS AREC are about to reach the first catch wire and going strong. When shoots are about 10-12 inches long, downy mildew, powdery mildew, and black rot tend to show up. Then, at bloom time, flowers and young berries will be susceptible to these diseases until 4-6 weeks after bloom.  In addition, Botrytis, ripe rot, and bitter rot can cause infection on flowers.  Thus, you need to consider multiple diseases management. However, you probably do not need to manage all with expensive materials. What you need to think about is which disease(s) have been the major issues at your vineyards. The disease history of your vineyards tends to repeat itself because of the environmental conditions at your site and availability of spores from previous infections.

Downy and black rot management depend on rains.  I have seen cases where downy or black rot developed before bloom under wet conditions. We receive a little fewer rains than last year, but it is always best to keep up with the protection. If you have concerns on downy or black rot, think about the use of a DMI (tebuconazole, Rally, etc., FRAC 3) or QoI (Abound, Pristine, etc., FRAC 11) material for black rot, and Phosphite (= Phosphorous acid, FRAC 33) or Metalaxyl (Ridomil, FRAC 4) product for downy mildew.  Revus and Forum (FRAC 40), Zampro (FRAC 40 + 45), and Ranman (FRAC 21), can provide a very good protection against downy mildew.

Although it has been relatively cold lately, once we start to see a trend of warm, humid nights, it would be a nice idea to think about downy mildew, since these humid nights can promote spore production of the downy mildew pathogen.  

As for powdery mildew, I prefer to start powdery mildew management (i.e., the use of a DMI or other newer materials such as Quintec (FRAC 13), Vivando (FRAC U8), Luna Experience (FRAC 7 + 3), Aprovia (FRAC 7), etc.) at pre-bloom application in our plots due to heavy powdery mildew pressure at our plots. It seems to reduce the cases of cluster infection for us.  However, please note that in my vineyards, our trials tend not spray as often as many of you do.

Development of Botrytis depends on what type of varieties you grow, as well as your canopy management strategies.  White-fruited varieties with tight cluster architecture tend to be more prone to Botrytis.  I.e., a red-fruited variety with loose clusters probably does not have many issues with Botrytis, especially if the canopy is well maintained.  Bloom time is important for Botrytis management because this fungus can infect flower and flower debris, and come back later when berries are maturing. There are a number of Botrytis materials such as Rovral and Meteor (FRAC 2), Elevate (FRAC 17), Vanguard and Scala (FRAC 9), Luna Experience, Kenja (FRAC 7), etc.

Warm weather conditions help the development of ripe rot and bitter rot.  Both of them cause infection from bloom to harvest; however, you do not see actual rots until near harvest.  It is very similar to Botrytis in this regard.  An additional issue here is that both diseases can change the flavor of wine.  If you have seen ripe rot or bitter rot, it would be a nice idea to protect flowers with mancozeb, captan, Ziram, or a QoI.

For Botrytis, ripe rot, and bitter rot, please keep in your mind that early season powdery mildew management can become important to prevent these diseases.  These pathogens are very good at infecting through wounds (plus, the flower infection of Botrytis requires wounds to become rot); thus, scars, which will turn into the opening of the skin, caused by powdery mildew infection on young berries can be the ideal targets for them.

Lastly, please keep in your mind about fungicide resistance issues.  You can locate FRAC code on the fungicide label (or you can take a look at our Pest Management Guide, which you can find on the right-hand side of this blog).  Even if two products are different in names or came from different companies, if they have the same FRAC code, they are basically the same regarding fungicide resistance management.  Please rotate the FRAC code.  For newer materials such as DMI (or SI) or QoI or SDHI, my recommendation is not to repeat the application more than twice, and limit the use of it to no more than three times a season. Less number of application is better for fungicide resistance management. (I.e., Use the same FRAC code only twice (maybe three times) per season, except FRAC codes start with M.)