Due to many rain events and relatively cold weather, it
looks like we are somewhat back in truck in terms of the growth stages. When
shoots are about 10-12 inches long (i.e., right now), 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, and young berries are susceptible until 4-6 weeks after bloom. In addition, Botrytis, ripe rot, and bitter
rot can cause infection on flowers. Yes,
it is a lots of diseases to think about. 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.
Downy and black rot management depend on weather
condition. I have seen cases where downy
or black rot developed prior to bloom under wet conditions, and this year would
be such a case, if you could not keep up with the protection. If you have
concerns on downy or black rot, think about the use of a DMI or QoI material
for black rot, and Phosphite (= Phosphorous acid) or Metalaxyl (Ridomil)
product for downy mildew. Revus, Zampro,
and Ranman, can provide a very good protection against downy mildew. Based on
the past few weeks of rain events and a trend of warm humid nights we observed,
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, Vivando,
Luna, 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.
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.
Warm weather conditions help 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. 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
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). 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 in terms of 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 two
times, and limit the use of it to no more than three times a season. Less
number of application is better for fungicide resistance management.
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