I have several roses that bloom just fine but one particular rose bush produces buds that never open. Why is this happening?
It is possible that your rose has a problem with insects like thrips, which can cause buds not to open. If you see tunneling in the buds (holes in the petals), it could be caused by beetles. There is also a possibility that a disease is causing the problem. Fungal infections like botrytis blight can result in buds which do not open, but you would probably notice signs of the fungus during warmer temperatures, such as gray-brown fuzzy growth, and blotched petals or drooping buds. The Northwest Center for Alternatives to Pesticides provides information describing various rose problems, and organic solutions.
Here is a description of botrytis blight from University of California, Davis Integrated Pest Management. This is a brief excerpt:
“Botrytis blight, caused by the fungus Botrytis cinerea, is favored by high humidity. Affected plants have spotted flower petals and buds that fail to open, often with woolly gray fungal spores on decaying tissue. Twigs die back and large, diffuse, target-like splotches form on canes. Reduce humidity around plants by modifying irrigation, pruning, and reducing ground cover. Remove and dispose of fallen leaves and petals. Prune out infested canes, buds, and flowers. Botrytis blight is usually a problem only during spring and fall in most of California and during summer along coastal areas when the climate is cool and foggy.”
The Olympia Rose Society also has information on these potential causes of failed buds. Below is their description of thrips:
“Buds do not open, or flowers are deformed. Petals have brownish yellow streaks and small dark spots or bumps. White and pastel roses are particularly susceptible. Thrips (are) tiny orange insects with elongated bodies. Thrips feed at the bases of rosebuds and on the petals of open flowers. They seem to be attracted to light-colored blossoms.”
The Organic Gardener’s Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale Press, 1996) suggests encouraging natural predators of thrips and, if the infestation is severe, spraying weekly with a safer insectidical soap or pyrethrin-based product. This same resource suggests that if your roses have botrytis blight, you will see the buds turn brown and decay instead of opening, and you should pick off and dispose of any diseased buds. They recommend spraying with sulfur once a week during the growing season.
A few things that are always a good idea when growing rose:
- make sure there is good air circulation around your plants
- don’t water from above the plants (keep the leaves dry)
- always clean up around the plants–don’t let leaf debris or any diseased buds lie on the ground under the rose bushes
This (now archived) site has many pictures of rose pests and diseases for you to compare with what you are seeing on your plant. Since I cannot diagnose the problem without seeing the plant, I recommend that you take samples of the affected buds to a Master Gardener Clinic.