This year in coastal NC, we experienced the hottest June on record & July is showing little improvement, so I've been dealing with the same issues/questions you are. I've been spraying between 5:00 & 6:00 am. If I couldn't get out that early, I wouldn't hesitate to spray very late in the afternoon/early evening. I also use Bayer, alternating with HonorGuard.

I've been keeping all my container roses very well hydrated, but am watering the beds deeply only on the day before I intend to spray (about every ten days), altho I'm not certain that's absolutely necessary. Some of the roses are not holding up as well in the heat as others, but I don't think any of them have suffered from being sprayed. It seems to me that at these extreme temps, retaining as much healthy foliage as possible is especially important.

Here's a link to an old thread that may contain some additional info for you to consider . . .

Here is a link that might be useful: Spraying in the Heat

Thanks Windeaux!! After reading that old post I guess it will be safe to spray. I really haven't been feeding them either and their leaves were starting to get yellowy with green veins so I fed them some this morning since we had such a good rain yesterday. Thanks for your help and I hope this heat lets up on us real soon. Take care, Judy

I find that if I use the Bayer product with just the slightest case of blackspot that many of the affected rose bushes' leaves turn yellow and fall off. I always make sure my roses are well watered before any spray cycle so I've never attributed the yellow leaves to the lack of water and spray combo.

Keep us posted on future occurences.

Adrian.

Above a certain temperature, Blackspot does not reproduce or infect leaves, so the theory goes that in extreme weather you need not spray.

From what I read the active temperatures are 59-81F, but it must be over 81F (I speculate!) all the time--if it cools down below 82F overnight, does the blackspot reactivate?

Here is a link that might be useful: university of FL: blackspot temperature range

I've been spreading out my spraying because of the heat. Not that it will hurt the roses, but it's not necessary. I have some BS on the worse subjects, and I am going to spray this weekend. As long as you do it before the sun is high, you should be ok. The Bayer isn't as photosensitive as some of the other sprays and there is no temperature warning on the label.

kublakan, the leaves that yellow and fall off are due to the blackspot. Not the Bayer spray. The leaves may not show the disease, but it will come out in the next day or so and then the leaves yellow and fall off.

My roses are doing the same thing with the yellow leaves, I also haven't sprayed in over a month and they are starting to show signs of severe blackspot. I get sorta of lazy about this time every summer....with the extreme heat and all the humidity, I just don't feel like being out there spraying, I wish there was an easier way but until then.....the leaves will fall....sigh....oh well.

In the heat of the mid south you can usually skip spraying unless the night time temperatures drop below 80. 80 however is only a general rule of thumb. During our last heat wave in the upper 90's, I skipped spraying even though the night time temps hovered around 78 to 79. Only one rose developed a minimal amount of B.S. and it's very prone to that disease (and will probably be replaced). I use Banner Maxx during high summer because it can go 3 weeks without repeat if conditions are relatively dry. I use Indicate 5 along with all my spray materials. Recently a rainy spell was predicted so I had to gear up to spray even though the front hadn't moved in yet and the temps/humidity were still high. I sprayed late in the evening when it finally dropped down to 89 degrees. The roses had been well watered beforehand. I did see some minimal damage to some of the rose leaves from burn, but it was certainly nothing like the BS I would have had during this period if I hadn't sprayed at all. Pick your poison so to speak. I always think about what Mike in Louisianna says about spraying, but the few times I've sprayed when it was in the 90's I'm sorry to report that I did have at best moderate damage. But maybe there were other differences in our situation.

Hoovb, WHAT?!?!?!? "Above a certain temperature, Blackspot does not reproduce or infect leaves, so the theory goes that in extreme weather you need not spray"?!?! And this preposterous theory came out of some place in FLORIDA? OMG, how far into the three digits does the temperature have to soar before that theory becomes operative? Can humankind survive temperatures that high?

The article says some astonishing something about BS thriving only between 59 & 81 degrees F. Well I'll be . . . 'Spose there's any way I can communicate that scientific fact to the fungi that's been the scourge of my garden for all these many, many hot summers?

Now I'm really ticked-off at my resident fungi . . . If nothing's supposed to materialize above 81 degrees, I should have been luxuriating lazily in a disease-free garden all these many, many very hot seasons. Am I P.O.'d? YESSSSS . . .

I don't think anybody on this entire planet will ever truly understand everything about Blackspot disease. lol

Here in southeast Kansas where the summers are usually very hot (as in 90+ degrees), I rarely need to spray for BS after the big spring flush. When it cools off in the fall, I may have to spray a couple times again.

I don't know that 90+ degree heat guarantees absolutely no BS, but it sure does seem to cut down on it rather drastically--which is fine with me! LOL

Kate

I do stretch my spraying out in the summer to 3 -4 weeks. But keep in mind that even if it's 100 degrees during the day, it does get cooler at night. So if the temps dip below that magic number, and it's moist, you can get BS. As I said upthread, I do have it on a few of the 'usual suspects', ZD, Peace and some of the others. But for the most part my roses have been clean this year. I have sprayed regularly and the hot/dry weather has helped.

jaxondel, hoovb is correct. She is talking about conditions for germination rather than survival of the disease. For summer germination you need wet leaves and some hours below 80 degrees at night. That commonly occurs in Florida summers, so you get germination all year around. In Texas, for example, it does indeed get too hot for blackspot during part of the summer.

Another determining factor aside from nighttime temperatures would of course be how blackspot resistant your roses are. If certain roses are consitantly having problems with blackspot you may want to check into more disease resistant varieties.