Happy 4th!

The thunderstorm on 7/01/09 lasted a little over an hour (0.73 inches); however, RH remained high for about 9 hours with an average temperature of 65F. Thus the event was long and warm enough for Phomopsis, downy mildew, and black rot infection, and powdery mildew ascospore discharge.

Also, we had nights with relatively high RH (>80%) in 6/29 and 7/2. If these are isolated events, you do not need to worry about; however, as we know, the early part of June was very wet and we had many nights with a favorable condition for downy mildew sporulation. Sure enough, when I checked vines yesterday, we had a lot of sporulations under side of leaves.
If you have seen these spores on many of your leaves, you may want to think about protecting healthy leaves and berries from next infection event, or use materials with a curative activity (Phosphorus acid, Ridomil etc).

The other disease I found quite a bit in our untreated vines are black rot. This is one of diseases which you really need to be on top of it to secure your yield. Here are some convincing pictures.

Here, you can see a path of infection from a leaf to berries…
Now you can clearly understand why it was named black rot…
Once again, the critical period of infection on berries for black rot, downy mildew, and powdery mildew is 4-5 weeks from bloom. If you protect your vines during this period, you should not see damages like these. In fact, a vine next to these vines which received a treatment is nice and clean!

I hope you will have a nice July 4th weekend. If you travel somewhere, please drive safely.

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *

© 2024 Virginia Grape Disease Updates - Theme by WPEnjoy · Powered by WordPress