|My rugosa roses are in their 2nd season. They are growing well, but some of the leaves have turned yellow and developed some black spots on them--they eventually shrivel & drop off. However, they have lots of buds and are beginning to flower. Should I spray them with something--I don't see any aphids or other insects? Is it a fungus? We have had a lot of rain and cooler temperatures this Spring in Chicago--is that the problem? Pleae advise.
|Based on your description it sounds as though they may have some blackspot which is a fungus and can appear in some years depending on the weather. (Rugosas normally do not suffer from it much if at all.) Controls would consist of mechanical means such as pick off the affected leaves, clean up the fallen leaves, avoid overhead watering, and hope for drier weather. Also, this winter, pick off any leaves that stay on the bushes, clean up the fallen rose leaves, replace the mulch, and be sure to remove any rose prunings from the garden. Then use a dormant lime sulfur spray in late winter per the label directions. This will help limit the chance of it appearing next year. Do not allow them to crowd as they need good air circulation and full sun. Rugosas defoliate if sprayed, so it is better to try to use these other types of control rather than use a fungicide -- in any case, blackspot would need to be sprayed for as a preventive rather than once it appears. I hope this helps.