rose buds infected

Asked October 4, 2019, 12:56 PM EDT

Can you tell me what is happing to this rose bush? (see photos) The new buds get black around the edges. I've tried spraying them with this peppermint oil from Tagawa's, but it doesn't help. My other roses are doing OK.
Thank you - Pat

Arapahoe County Colorado roses

1 Response

Roses often have several insects and disease issues that cause brown buds:

  • Cold weather can cause buds to fail, such as the cold, wet weather we had in June. Also, 7 of the last 14 days, temperatures have fallen below 45°F which can cause bloom fail. Clip off the brown buds and consider covering your roses with a frost blanket at night to extend the blooming season.

  • Thrips (very tiny insects) attack rose buds in the early stage causing buds to turn brown and failure to open, or only partially open. The brown edges of the petals appear to stick together. I cannot find where peppermint oil is effective in controlling thrips, but the age of the oil may hinder effectiveness. Here is some additional information on thrips including controls:

    https://entomology.ces.ncsu.edu/thrips-2/

  • Botrytis blight, Botrytis cinerea, is commonly known as gray mold which causes the buds to turn brown and decay instead of opening. The mold spores land on the plant, infecting leaves and stems and ultimately the new buds. This can be treated with a rose fungicide, spraying the entire plant (tops and bottoms of leaves and stems). This fungus is most common when temperatures are 62 to 72°F and conditions are moist.

  • Inadequate watering, especially in intense heat, can cause buds to brown and die as well. Leaves will also turn brown which doesn’t seem to be the case with this rose. These leaves look healthy, although there appears to be powdery mildew.