Late seson rots management tips

There are chance of rain (40-70% across the state) predicted during tonight to Saturday. We really need some rains, so, I'm hoping that we all will get a decent rain.  We will see...

Now probably many of you are considering disease management at or after veraison.  One of diseases you may be concerned at this time of the season are late season rots (sour rot and/or Botrytis gray mold, caused by Aspergillus niger, Alternaria tenuis, Botrytis cinerea, Cladosporium herbarum, Rhizopus arrhizus, Penicillium sp., and others).  These late season rots come in when fruit sugar content accumulates around 8%, and often times, white varieties with tight clusters such as Vignoles and Chardonnay, tend to get this disease more than other varieties because of the structure of the cluster which can hold water inside and also because of the fair skin.

The sour rot pathogens, including Botrytis, are opportunistic in nature, and the damage and the risk will increase if Botytis rot is involved.  Typically, Botrytis management needs to be done at early in the season.

• For example, at bloom powdery mildew management is a key because once these young berries are infected by powdery, even to the point that you don't really see symptoms, it will damage grape berry skin enough to cause wounds later in the season to invite these rot pathogens in. 
• Botrytis can infect flower part as well, thus, if it often recommended using Botrytis specific materials at bloom. 
• With the same logic, the management of grape berry moth, wasps, and birds can lower the risk of infection.

The cultural practice plays a very important role on the late season rots management.

• Proper shoot positioning and canopy management will decrease the risk of Botrytis infection by lower humidity of the fruiting zone.
• Leaf removal around fruit set has been recommended for some varieties to increase the air movement around clusters.
• Leaf removal around veraison will help thickening of skins.
• Thus, some people perform leaf removal around fruit set to open up the eastern-side of canopy and do it again around veraison to open the western-side.
• However, it may also increase the risk of sun damages on the berries, thus, check to see if the leaf removal is a good tactic for your varieties.
• Bunch thinning can also be done at veraison to reduce the risk of having berries with high sugar lying around the vineyard to invite insect pests.

There are only a few options with the chemical management against late season rots, and none of them will provide a complete control.

• Botrytis materials such as Rovral, Elevate, Pristine, etc., and captan is often recommended.
• In addition, the use of a copper fungicide (Bordeaux mixture, etc.) has been recommended as a tank mix with a Botrytis material because in addition to its fungicidal activities, some study showed that copper helps grape berry skins to become thick.