Disease defoliated my roses last year - don't want a repeat

[RoseGirl]

USDA Zone 8a
Oak trees are around the property but not on it. One of them is >200 years old and has a huge canopy, so the acorns and leaves go everywhere. I feel like I do an okay job of keeping the leaves off the rose plants, but it’s probably impossible to do a perfect job.

Okay, long post incoming…
TL:DR; 100% defoliation of every rose in my garden in 2025, also yellow canes on 3 plants, and a few pics of Chicago Peace just as a focus.

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In different areas around my house I have America (x2), Chicago Peace, Julie Andrews, Nicole, Morden Blush (x2), Knockout (x2), Don Juan, and Miracle on the Hudson. I also have an unidentified cultivar that was probably planted when the house was built, and there are a couple wild roses near the edges of the property. Don Juan, America, and Knockout are in their 3rd years, the rest of the ornamentals were planted in early 2025.

In 2025 all of my ornamental roses got completely 100% defoliated by about May by Blackspot. Afterwards they would try to leaf, but the leaves would instantly become infected again and die. It rained basically every day April-June in 2025.

Don Juan had what appeared to be the same problem, plus yellow canes in 2023 and 2024 - it’s never been healthy. It might also have had a drainage issue which I mitigated as a last-ditch effort in the summer last year. But it’s about 10 ft from the nearest rose (unidentified one that came with the house) and 15 feet from the next nearest. I thought Don Juan was going to die entirely, but so far it’s putting out new growth this spring.

Knockouts seemed the hardiest, but even they got defoliated by early fall.

Anyway, last year I ended up buying some mancozeb powder to be used as a spray, and also the bio advanced 3-in-1 liquid mix-in, and I applied those a couple times each in the summer and fall but it was of course too late for flowers. Fall 2025 I pulled off every last dying leaf of all the plants and cleaned up around their bases. Local oak trees dumped their leaves Nov-Dec, but I’ve been trying to keep those away from the roses too. Towards end of fall, after the last application of the mancozeb, the leaves the roses put out did manage to survive a few months until we had two hard freezes in January, and they got frost damage. But I feel like that was a success for the leaves to last more than a few months with no black spot! But as a fungus, I think it also got suppressed by the cold.

About 1 month ago all the roses started putting out new growth. I mulched with pine bark from ACE and I did an application of Mancozeb about 3 weeks ago.

Chicago Peace had some yellow canes, here is a photo:

I cut this off at the time, but just wanted to show the picture I took.

Now it’s 2 weeks later and the leaves are coming in, but I’m seeing the very very beginnings of blackspot once again. About half of its leaves already have little tiny black dots. I’m afraid they’ll grow and defoliate it again. Forum says I can only post 1 media item per post, but I do have more photos.

My plan today was apply the liquid type bioadvanced 3-in-1 to the roses, but seeing the start of black spot on Chicago Peace just 3 weeks after spraying it with mancozeb got me so disheartened that after I did that I came here to look for any advice y’all can give.

Sorry for dumping so much info, I just wanted to provide as much context as possible.

[RoseGirl]

Very small beginnings of black spot on Chicago Peace taken today. The leaves started shooting out maybe only 4 or 5 weeks ago. I sprayed with Mancozeb about 3 weeks ago. Applied Bio-advanced liquid rose 3-in-1 (mixed into water) today to the base according to instructions on the container.

Half the leaves on this plant already have these tiny beginnings of blackspot.

[Rosejoy]

Welcome here Rosegirl,
Mancozeb is a contact fungicide, it only lasts 5 days at most on your rose leaves, it is not a preventative. The Bioadvanced is ok, but there are better systemic fungicides that get into the leaves and prevent the Diplocarpon rosea (black spot) spores from growing.
Take a look at Eagle aka Myclobutanil and Honor Guard aka Propiconazole, you can buy them and they are very concentrated. You only need 1/3 to 1/2 teaspoon per gallon. If you spray every 10 days when it is wetter you will have better results, then every 14 days once it is dryer. Spraying Mancozeb every Three days for Three times will help you get control of the black spot, then start combining the Mancozeb with your systemic fungicides. I also use a product that makes the water wetter and lowers the pH, like Indicate 5, but Southern Ag sells Tweak which is a lot cheaper. Some rosarians add 1 tablespoon of white vinegar to lower the pH of the water with a some liquid soap.

[spencer]

a few questions for you, rosegirl: (similarly tediously long, because even if you know this stuff, others who don’t know this stuff might want to hear it…….and all this is just preliminary… there’s SO much more detail to each point)

what type of soil would you say you have? clay? hard clay? sand? just so nice perfect loam? can you push a shovel in with moderate pressure, down to at least half the blade? if you push the shovel in with great effort, are you able to remove the shovel without great effort? do you hit rocks? each of those soils have different water retention properties.
clay holds on to water for days. but water drains down out of sand in hours.

how much water, how often do you water? too much water breeds too much blackspot and other diseases. even the excellent products and treatments suggested by rosejoy cannot overcome water-logged soil.
rose roots need just as much air in the soil as water. if you fill the soil with water, there’s no room for air. the lack of air enables the various fungal diseases to multiply (cuz i couldn’t spell proliferate).

i suspect your roses are always too wet. either too wet, or way too wet.

water just enough for the soil to be moist. actually stick a finger into the soil, more than 1 knuckle deep. if the soil feels wet, or squishy, that’s too wet.
if the soil feels cool and damp, almost too wet.
cool and moist but not damp, just right.
dry and dusty? not moist enough. don’t ever let the soil dry out enough to be dusty crusty.

so, each day, test the soil to know if it needs water, and develop a feel for the amount needed.

do you have an irritation system? if an automatic system, do you know how long and how often the zone runs, do you know the flow rate to determine the total amount of water per area around each bush?

are you watering by hand with a hose or a bucket? do you know the flow rate of your hose (i bet almost no one knows.) count how many seconds it takes to put 1 gallon into a bucket. remember that number. bigger diameter hoses give more water. longer hoses give less water. time it to know. typically, hoses give a gallon in 8 to 12 seconds. typically, in average soil, most of the roses i deal with need 12-15 or so seconds, when the bush is about the size of an adult person, usually twice a week (but this depends on the weather. more details). i would rather water more often, than add more water all at once.

and, not all roses want the same amount of water. some want to be dryer, some need to be moister. trial and error, experience and paying attention to each of your pets will give much better results.

and, just for fun…. is your water from a well, or town/municipal supply? did you ever get a water test? would be very interesting to see the results. most people don’t even question what’s in their water. let’s find out!

good for a start, and, apologies for the length.