Spots on Rose Leaves

[baileybird]

Have a mixture of roses - climbers and standard - in my front garden against the front of the house. This year they seem diseased - leaves covered in black marks and leaves look yellowy. Roses appear to be more wild looking too. Any ideas what this is and how do i tret it?

Thanks so much - Heidi

[Clanad]

Yes, but hurry... You've experienced a wet, humid summer so far, right? Then you've also experienced Black Spot.

This is a common fungal infestation in Roses. Some are more resitant than others. The fungii spores must be wet for at least 7 hours before they can germinate and do so at temperatures above 75 eegrees or so (F). The spores are resident in the leaves and other organic matter around the base of the plant, so you didn't do a very good job of clean up after last growing season, eh?

The spores infect the leaves nearest the ground and give off a gas which in turn moves the spores and infestation up the plant. Starts as Black Spots (what else?) on the leaves which soon turn yellow and fall off. Left alone the entire plant will be denuded. The plant will be weakened and probably die by next growing season.

So... here's the plan; clean the base of the plant down to soil. Next, prepare a solution of chlorothalonil... here in the U.S. I use Daconil, but several other brand names will do. It's also called Dormant Oil and be careful mixing and spraying out of a pressure sprayer, since it's sulphur based and smells terrible, though not hazardous. After snipping off any canes that are thoroughly infected, spray the remaining ones and their leaves thoroughly... really wet them down top and bottom. Repeat in about 10 days (no more than 14). Do this for at least two or three cycles.

The plant should recover, but produce few blooms this year. Finally Clean it up! this fall before freeze-up. I'd also recommend spraying the ground around the base of the plant either this fall after the plant goes dormant or early next spring just as new growth appears...

You can probably find ready-mixed formulas in hand sprayers if you don't have a lot of roses...

Best of luck! Clean-up!

[baileybird]

Thanks for this - however - I did clean up thoroughly last year and they were properly pruned too.

It appears to be all over the rose bushes so I may just call it a day as if I remove infected areas - there willl be nothing left.

Will consult a garden centre in UK to see what they have avilable and if this is feasible.

Again thanks for your reply.