Black rot is the most common cause of that. Sprays in spring are required to clear it out of the vineyard. It is hard to treat organically; copper is probably the most effective spray. If you use synthetics then Immunox does a good job on it. Different grape varieties have very different degrees of susceptibility.

Scott

The other spray for this is Nova Rally. Strong stuff. Recommended by Cornell for black rot, for what its worth.

Dan, Immunox, Nova, Rally, and Eagle are all myclobutanil, the same stuff. Home growers can generally only find Immunox readily available.

Scott

Black rot. The controls must be correctly timed. Two sprays of mancozeb (new growth and pre-bloom) followed by two sprays of myclobutinal (post-bloom and pea sized). The first (new growth) spray is not as important as the next three, which are absolutely critical. But if you can get the first spray in, it would help.

The reason for the program is that while mancozeb will completely control black rot by itself, it can only be applied up to 66 days before harvesting, Depending on the variety, you may be bumping up against that limit by the time of those third or fourth sprays. Hence the switchover.

This post was edited by nickl on Tue, Jul 30, 13 at 0:30