We are taking a look at one of the bad guy insects in the rose beds here, the rose curculio or rose weevil (Merhynchites bicolor). This little menace is a dark reddish and black weevil with a distinctive long snout on its head. The rose curculio is about 1/4 inch (5-6 mm) in length and its long snout is used for drilling into and feeding on flower buds. Yellow, light pink and white colored roses seem to be its preference to feed upon.
Rose Curculio Damage
If your rose blooms have petals that look a bit like Swiss cheese, have young buds that have failed to open and are dried up, or have stems that are broken just below the bud, it is likely that you have been visited by rose curculio weevils. If left uncontrolled, they will totally take out your rose bush blooms!
Keep an eye out for them and the damage they cause starting in late May to early June, depending on climatic conditions. These nasty visitors drill into the rose and lay eggs in the hip or ovary area. The eggs hatch and the small, legless white larvae feed on the rose blooms and the reproductive parts of the rose bloom, seeds and petals as they mature. Like the Japanese beetle, the larvae then drop to the ground to pupate in the soil over the winter.
The adult emerges from the soil in late spring, then crawls up to feed on the rose buds, thus starting the reproductive cycle all over again. Fortunately for our roses and us, there is only one generation a year. A major infestation of these weevils will eliminate all blooms from a rose garden. It is best to take action at first notice of their presence to be successful at managing rose curculio pests.
Rose Curculio Control
Controlling only a few of these pests can be done by hand picking them off the roses and destroying them. Larger numbers will likely require the help of an insecticide. To truly gain control, both an insecticide approved for soil use and a spray type insecticide will be needed. The soil use insecticide will go after the larvae in the ground and the spray insecticide will go after the mature weevils.
Insecticides listed for the control of beetles on roses and other ornamental shrubs should work on rose curculio weevils. Read the label on products at your local nursery, garden center or those available online beforehand. Be sure to read all of the listed precautions and directions for proper use/application thoroughly.