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When to start treating for blackspot?

Posted by davidchance 7a (My Page) on
Wed, Mar 7, 12 at 12:26

Sorry for the beginner question.

The weather here in NJ has been really warm this winter, and most of my roses are already starting to leaf slightly.

Last summer some of my roses got blackspot and I was way to late to respond to it so by late summer they were nearly 3/4 bare canes.

So when would be a good time to start spraying?

Follow-Up Postings:

RE: When to start treating for blackspot?

Disease can spread as soon as leaves have expanded. Blackspot germinates when leaves are wet continuously for 8-12 hours with temperatures staying between 60 and 78. I am not sure whether it germinates with temps in the 50s, but, if so, it probably requires longer wetting. So what you want to watch for is mild, humid, drizzly days. It will be too cool at night for a while. With the Bayer tebuconazole fungicide, you can spray up to a week after germination and still stop the infection.

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