Plant architecture influences disease development. Roses that have a more compact form or that develop leaves near the ground are more subject to infection. Crowded plantings generally have higher humidity within the canopy which promotes disease development. Prescription for Healthy Roses Effective black spot control depends on an integrated approach that uses timely application of appropriate fungicides and the implementation of good horticultural practices. These are designed to prevent severe infection, which can defoliate plants by mid-season.
Control starts with growing cultivars resistant to black spot.
Most garden catalogs will identify cultivars resistant to black spot and other rose diseases. For the home gardener who wants to grow a few roses in the landscape, but does not want to be burdened with a fungicide spray program, black spot resistant roses offer a suitable solution. For those dedicated enough to follow a weekly fungicide spray program, black spot susceptible cultivars offer a challenge. Successful control requires weekly application to protect the newly emerging foliage. Apply fungicide sprays in the evening when there is less wind and temperatures are cooler.