Answer: Deformed flowers can be caused by very tiny four winged flies called thrips. This little pest can cause a lot of damage as it hides in the base of the infected flower bud and sucks out the sap. The best control is to cut off all infected areas. Deformed flowers can also be caused by rose curculios or rose weevils. Rose curculios overwinter as pupae in soil, emerge as adults in spring and early summer and crawl up to feed on flower buds. The adults lay eggs in hips and flower buds, where small white larvae hatch and feed within the flower bud. Buds damaged by larvae will often be deformed. Buds may not open or will open deformed. The larvae emerge from the buds and drop to the ground to pupate in soil until next season. After the egg-laying period in late May and June, adults continue to feed through the season. Usually found in or near flower buds, rose curculios are chewing insects, with biting mouthparts on the end of their long snouts. They drill holes in buds, which then fail to open, or open with petals riddled with holes. Larvae feed on the reproductive parts of the flower, seeds, and to some extent petals. Serious infestation can prevent almost all bloom. (Curculio damage will be holes in the petals, while thrips damage will be brown edges or streaks.)
You can reduce future populations by removing spent blooms and hips, and removing any damaged blooms. Current populations can be reduced by hand-picking, or by applying contact (insecticidal soap, neem oil) or ingested (Orthene) insecticides during the active season, in late May and June. The larvae within the buds cannot be controlled by insecticides, although pirate bugs can be effective; control is best managed by removing deformed buds and spent blooms before the larvae emerge.
Q&A Library Searching Tips