Roses; fungus

Asked June 18, 2013, 11:33 PM EDT

Hi there. I have a bed of rose bushes--about 4 of them with some ground cover beneath. (This is only my second summer with them; they seemed to do okay last summer when we first moved to this home.) Anyway, I think they've got blackspot or some kind of fungus, and aren't blooming much. When they do bloom, they wilt very quickly. We're only getting a few blooms at a time, and the leaves on all the plants have blackspot. I've been using a fungicide (from a can) I bought at the garden store, but it doesn't seem to be helping.

Marion County Oregon

3 Responses

Thank you for the picture. Yes, it is the disease known as black spot. A fungicide will not cure any of the affected leaves. Generally speaking, roses do not want vegetation around their base. Culturally you can mulch, but do not use anything which collects moisture touching the stems. High humidity encourages fungal diseases.
You need to pick off and remove from the garden all affected leaves. Then you can use an approved fungicide to protect the undamaged foliage. Some of that foliage may already be invisibly infected, so the leaf removal has to be on-going. A fungicide with Potassium bicarbonate usually works well. Give each bush a cup of alfalfa pellets or meal as well. If there is good light and air circulation through the bush, that really reduces the problem. The root problem is that some roses are very prone to disease and require frequent and thorough sprays to look good. Others are almost carefree. Variety is very important in roses. There are many fragrant, lovely roses which are almost immune to disease now. I would guess that using an aerosol can to spray will not be cost or control efficient. You need to thoroughly wet the bush and that will require a regular sprayer.
I hope this helps you and your roses. If you have followup questions please feel free to ask.

Thanks so much for the advice and feedback. Very much appreciated!!