|i purchased 16 dream roses last year = having been told they are resistant to black spot. but they were dessimated by the disease. comments please.|
|These roses are considered disease resistant, however that does not make them disease proof. In your area, the climate is truly conducive to black spot and other fungal problems on roses. It may be unrealistic to expect the plants to be totally black spot-free.
There are some cultural methods to follow to try to reduce the incidence. Begin by planting the roses in full sun and in a location with good air circulation, plant them far enough apart that air can flow between them and neighboring plants. Make sure they are watered deeply in times of drought by soaking them at the roots, not by overhead watering. Avoid wetting the foliage, especially in the evening.
Prune them back as directed by the breeder who developed them, to about ten inches tall each spring about when the trees leaf out. Next, remove any leaves that may have stayed on the plants over winter, to try to limit sources of reinfection. Put the clippings and old leaves in the trash -- not in the compost. For the same reason, remove the top layer of mulch and replace it with clean fresh mulch.
Finally, you may want to try a preventive spray containing lime sulfur during the dormant season, or possibly experiment with a neem spray during the growing season. The neem tends to have antifungal action as well as repels the dreaded Japanese beetles.
I'm sorry you have been disappointed with your roses, with a little extra care I hope they will perform better for you this year.