Blackspot is a common disease of susceptible rose varieties. This fungal disease presents dark, circular lesions with feathery edges on the top surface of the leaves as well as raised purple spots on young canes. Infected leaves often turn yellow between the spots and drop. The infection usually begins on lower leaves working its way up the plant. High relative humidity (>85%), warm temperatures (75-85 degrees F) and wet leaves (6+ hours of wetness) are ideal conditions for blackspot. New leaves are the most vulnerable.
Blackspot can survive on fallen leaves or canes and spreads through splashing water. Following proactive cultural practices can prevent blackspot from entering your rose garden.
1.) Plant roses that are resistant to blackspot. Here is a resource from Purdue University that offers suggestions.
2.) Use drip irrigation and/or water carefully to keep droplets off the leaves.
3.) Plant roses in sunny locations with good air flow so wet foliage can dry quickly.
4.) Remove fallen, diseased leaves and prune out infected canes to reduce the spread of the disease.
A regular spray program can be used to protect your plants using a 10 to 14 day schedule of fungicides. Recommended fungicides include: tebuconazole (BioAdvanced Disease Control for Roses, Flowers and Shrubs, BioAdvanced All-In-One Rose and Flower Care), myclobutanil (Immunox, F-Stop Lawn and Garden Fungicide) and chlorothalonil (Broad Spectrum Lawn and Garden Fungicide, Garden Disease Control, others). (Cynthia Domenghini)
Blackspot can survive on fallen leaves or canes and spreads through splashing water. Following proactive cultural practices can prevent blackspot from entering your rose garden.
1.) Plant roses that are resistant to blackspot. Here is a resource from Purdue University that offers suggestions.
2.) Use drip irrigation and/or water carefully to keep droplets off the leaves.
3.) Plant roses in sunny locations with good air flow so wet foliage can dry quickly.
4.) Remove fallen, diseased leaves and prune out infected canes to reduce the spread of the disease.
A regular spray program can be used to protect your plants using a 10 to 14 day schedule of fungicides. Recommended fungicides include: tebuconazole (BioAdvanced Disease Control for Roses, Flowers and Shrubs, BioAdvanced All-In-One Rose and Flower Care), myclobutanil (Immunox, F-Stop Lawn and Garden Fungicide) and chlorothalonil (Broad Spectrum Lawn and Garden Fungicide, Garden Disease Control, others). (Cynthia Domenghini)
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