Get calcium nitrate and dissolve two teaspoon calcium nitrate per gallon, add a few drops of soap for sticker and spray the stems and the buds before the flower would open. [If the search engine works by any chance I am sure you could find the post by MichaelG and then please, check if I quoted the amount correctly] 5 lbs calciumnitrate costs between $3-$5 and will last forever. Simple and cheap solution. It works.

Or, you can buy Decree fungicide that is manufactured specially to treat botrytis. It isn't going to be chep: 1 lb is around $100.

Your choice :-(

Where do you buy calcium nitrate? I have this same problem and didn't know what to do for it....

FWIW, some roses are simply more subject to this problem than others.

Jeri

Farmer's Supply stores, fee stores (?) or specialty nurseries sell calcium nitrate.

FWIW, in my coastal region a rose that does not get botrytis is the exception not the rule.

If it's Botrytis blight sooner or later you'll see a fine gray mold (fine strands of a gray fungus) arising from the dead areas. Unless you've had a lot of wet, cool weather you probably aren't dealing with Botrytis blight.

So if it isn't botrytis, what else would make my roses do this?

Can you post a picture of the problem you're seeing? That will give others the chance to look for themselves. A lot of people here are very experienced and it may well be that someone will have a good piece of advice for you.

If you have a Botrytis problem it is usually easily dealt with by applying a fungicide, but even more straightforwardly dealt with by opening up the bush with some pruning in that area. Since the causal fungus requires cool wet growing conditions opening up the bush (which dries things out by exposing that part of the rose to more air) kills the fungus and stops the problem.

Dead areas are caused by a number of problems, some fungal and some not.

Since the causal fungus requires cool wet growing conditions opening up the bush (which dries things out by exposing that part of the rose to more air) kills the fungus and stops the problem.

That is the usual advice. However, roses don't read. You should see my garden when is very hot but also very humid and botrytis is rampant.
Very high humidity cancels out the 'col wet conditions' and botryitis rule in summer if I don't spray to stop it. Calcium nitrate w a bit of sticker is the least costly solution. It also used by the florist industry.

Is your strain resistant to Daconil?

I don't know, I used Daconil a long time ago. But spraying with calcium nitrate is less hazardous to your helath and by using it I fertilize at the same time. Also, it is much less expensive than any fungicide. So why should I experiment with other stuff? I still have some Decree but its price is like gold's.

Plants don't read, but pathologists pay close attention to the growing conditions for fungi so they can offer advice to farmers that's actually helpful. My guess is your fungus in the summer is another blight (so you still end up with the same problem as far as the plant's concerned, although the pathogen is different).

We had a long discussion about it two or three years ago. MichaelG suggested that it should and could be alternaria blight.

Comparing my roses to the very few photos of alternaria available I had serious doubt that it could be anything else but botrytis. I also sent photos to NCStte univeristy that provides consultation and does lab tests for Extension Services. They came back with Botrytis. I also sent them samples but by the time they got it the samples were contaminated with something that is present on dying tissues. They ruled out alternaria - the guy who answered my emails and dent the report on the samples is an expert on alternaris, so I guess, if he rules that out, I should accept this as a fact.
So still don't know the scientific answer but those roses of mine sure looked botrytis ridden to me.

I also found a paper from Brazil that stated that if humidity's is over 90% for many hours, botrytis spores could survive up to 112F. Here, relatively close to the coast we have o0ver 90^% humidity and dew from early evening till mid morning.That amounts to more than 10 hours, rather more. This again leads me to believe that was botrytis I had.

Baldo also said the Botrytis is a year-around problem in Hawaii.

I also found a paper from Brazil that stated that if humidity's is over 90% for many hours, botrytis spores could survive up to 112F.

Ah! Thank you! So the crucial issue is the level and duration of humidity. I will remember that for future reference!