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Why
Roses Won't Bloom By: Sandy Feather ©2006 Penn State Cooperative Extension |
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Q. I have two
beautiful rose bushes. The plants are lovely but produce no roses.
The buds turn brown, and no flowers develop. Last year, I had only
one flower on one bush and none on the other. The bushes themselves
are very healthy; I even had to trim the one back because the canes
were getting too long. Do you have any ideas as to why my roses do
not bloom, and what I can do to have flowers this year?
A. Rose buds that turn brown and fail to produce flowers are classic symptoms of attack by an insect called the rose midge (Dasineura rhodophaga). Rose midges can also damage vegetative buds and stems and cause deformed flowers that do not open properly. This pest overwinters as a pupa in a white silken cocoon in the soil under infested plants. Adults emerge in late spring as soil temperatures warm. You may get to enjoy the first crop of roses if soil temperatures remain cool early on, but once the adults emerge and begin laying eggs, you would be lucky to see even one normal flower. Many generations develop through the growing season.
Female adults lay their eggs in flower buds or expanding leaf buds or even the tender tissue of elongating shoots. Those eggs hatch quickly, and the young larvae immediately begin to cut into tender buds and stem tissue to obtain the sap. The injured tissue dies, turning brown at first, then black. It is common to find as many as 10 to 15 larvae on a single bud. They are very tiny, less than 2 millimeters long. You can see the creamy white to pale red larvae on close inspection. It only takes about two weeks for them to complete their life cycle during warm summer weather. Adults are inconspicuous reddish-brown flies. They do not feed at all and only live for a day or two. Controls targeted at the first generation can drastically reduce or even eliminate the need for treatment later in the season. Bayer Advanced Power Force Multi-Insect Killer (cyfluthrin), Bayer Advanced Garden Rose & Flower Insect Killer (cyfluthrin and imidacloprid), and pyrethrins and piperonyl butoxide are labeled to control rose midge in Pennsylvania. Start making applications as roses begin to leaf out in the spring. Make two more applications at 10-day intervals to ensure good control. Although many organic gardeners prefer to use pyrethrins without piperonyl butoxide, pyrethrins alone may not provide significant control. Some sources suggest that BioNeem (azadirachtin) may provide some control of this pest, but Penn State University's Woody Ornamental Insect, Mite and Disease Management guide does not list it. |
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