Moldy Roses - Knowledgebase Question

San Marcos, CA
Question by marqu003
September 24, 1999
My new "JFK" rose bush seems to have mold on it. Not only the leaves, but the new buds as well. It has only been in the ground a couple of months. Any suggestions?


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Answer from NGA
September 24, 1999

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"Mold" isn't a very descriptive term, and roses are susceptible to many fungal problems when climate or growing conditions do not suit them, so I'll guess that the flowers formed but failed to open, and then became moldy.

If this describes your rose, perhaps your plants have bud blast, the drying up and failure of flower buds to open. It's a physiological condition with many possible causes, such as root injury, cold soil, high temperatures during cloudy weather, dry conditions during formation, a lack of potassium in the soil, or excessive shading. Do you think any of these conditions are present?

Roses need two things for blooms: sun and nutrients. Are your plants receiving at least 6-8 hours of sun daily? Roses are heavy feeders during their bloom period. Nitrogen, phosphorous and potassium are the 3 major nutrients for all plants. (They correspond to the 3 numbers on fertilizer packages.) Nitrogen promotes growth of green leaves. Phosphorous is essential for blooms. If you are not already, I suggest you apply a rose fertilizer. The second and third numbers on the package should be higher than the first. Or, roses benefit from applications of
greensand, which contains potassium, and bone meal, which contains phosphorus. Both of these nutrients are important for flowering. The thing to avoid is feeding them with high-nitrogen fertilizer that will encourage foliage growth at
the expense of flowers. Keep them consistently moist and mulch with 2-3 inches of compost to help maintain soil moisture. Rosarians I know fertilize their roses every 6 weeks during the blooming season.

Another possibility is rose midges--teeny, tiny bugs that cause new growth, especially buds to shrivel and turn black. Insecticidal soap can help. You might need a magnifying glass to see them, or tap a bud over a piece of white paper and see if they fall out. I hope this information helps.

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