Black edges on rose petals
I have a rose bush that keeps getting black edges on buds and petals. I have sprayed for several weeks in succession with an anti-fungal, Captan, but it doesn't seem to help. Is this a mold problem, and can you recommend a type of treatment?
I water (sprinkler system) 3 times a week just before sunrise.
McLennan County Texas
Thank you for your question and submitted photos.
The damage looks like possible Botrytis infection. Typically this is an opportunistic disease. Captan would not be very effective. If this is happening on majority (80% or more) of your plant than I would suggest the following:
1. Look at plant and growing area to ensure that plant is not stressed. ie. ensure good drainage (no standing water as base).
2. Limit overhead watering (ie sprinkler or hosing), rather use drip hose or hand water at base to prevent wetting leaves and blooms.
3. look at foliage to see if any other symptom is present - possibly indicating other primary problem.
4. Use protectant fungicide such as those containing chlorothalonil (Fertilome Broad Spectrum lawn and Garden spray) or any product that has botrytis listed on the label. Read and follow label for proper rates and application frequency.
Please note that chemicals (natural or conventional) will not be very effective if the primary problem is due to external stresses on the plant.