If you have roses in your garden, right now would be a good time to examine your rosebuds. Look closely for small circular holes in the buds, and in blossoms that have already opened.
These holes were caused by the rose curculio, also called the rose weevil (Merhynchites bicolor), which is a kind of beetle, about one-quarter inch long.
The rose curculio’s damage ruins the blossoms and could ruin the entire plant if the gardener allows the insect to reproduce freely.
Fortunately, the rose curculio is fairly easy to control because its life cycle takes a full year and follows predictable stages.
Beginning in late May, the females crawl up the rose bushes to lay their eggs. Using their long snouts, they chew into the buds to feed and then turn to deposit their eggs in the buds. They could make multiple holes into a bud, and damage several buds.
When the eggs hatch, the legless white larvae feed on the buds and on the blossoms as they mature. The buds often are weakened by the adult’s feeding and fall to the ground with the larvae still inside.
The larvae burrow into the soil to pupate over winter, and, as adults, emerge in the late spring to continue the reproductive cycle.
There are several ways to interrupt this cycle and avoid damage to your roses. The timing of your controlling action is important in blocking the creation of a new generation of insects.
Starting in April, examine your roses to spot the adult rose curculio. They prefer roses with white or yellow blossoms, but could also be found on pink roses.
When you find rose curculios, either pick the insects by hand or shake branches to make them fall on to a cloth or bucket. They will play dead, but will soon revive and crawl back up the plant, so don’t be deceived: drop them in soapy water, where they will drown. You could also spray the adults with insecticidal soap or neem oil, but this treatment requires direct contact will not affect the eggs or larvae.
Predatory birds can be important allies in this process, so take steps to make your garden hospitable to birds by providing them with food, water, and shelter…and keeping synthetic chemicals out of your environment.
When you see damaged buds or blossoms, remove them immediately and dispose of them through the green waste (not the compost). Be sure to remove drooping buds. These buds have been weakened by the rose curculio and could already be supporting its larvae.
Once the larvae are in the soil, control measures are still possible. The most effective organic option is the importation of insect-parasitic nematodes, tiny worms that are natural predators of the larvae, and might already be present in the soil. These nematodes, which have been called “biological insecticides,” can be purchased from garden centers or the Internet, and imported into the rose bed.
With fairly easy but timely efforts, you can control this pest and enjoy your roses in their undamaged, beautiful form and color. The roses are looking particularly good this year, and definitely worth protecting.