For the last couple years, on my seemingly healthy rosebushes, the early new buds wilt, turn brown or black and fall off, and the stem and foliage right there also turns black. There are no marks or damage further down the stems and I don’t see any bugs. I lose all the flowers for the summer but the problem seems to stop later in the year and I get some fall blooms. What’s going on and what can I do about it?
Sadly, it sounds as though your garden has been infested by rose midge, a very challenging creature to manage. The symptoms you describe are exactly the kind of damage they cause.
The rose midge is a very tiny white fly larva that feed in clusters at the bases of rosebuds. It has a very short life (2 weeks) half of which can be spent in the soil below the plants. You want to destroy the midges that are on your plants and you want to prevent the generations of larvae that are form in the soil from coming up onto the plants.
There are no chemical treatments available in Canada, but there have been several studies conducted at various institutes and universities trying to find an organic solution to the problem. At this point the primary recommendations are 1) to prune off and destroy the damaged parts as soon as you notice problem (do not put the material in your compost), 2) make sure the ground around the plants is kept very clean with no plant debris and 3) to cover the soil around the plants with plastic (garbage bags or the like). If you cannot get the problem under control with these methods, you may have to resign yourself to the loss of spring and summer flowers. As you’ve noticed, the midges usually disappear by September.
Good luck with this troublesome pest!
Dr. David Shetlar, The Ohio State University, OARDC/OSU Extension: “The Rose Midge! (and other common insect/mite rose pests)”
Olympia Rose Society: http://www.olyrose.org/pests.htm