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Rose Insect Pests

The early bloom of roses has made them a popular landscape plant in Colorado. Insects also enjoy the flowers, and roses are rapidly becoming the victims of their own beauty. Look closely at flowers for signs of attack:

  • If flower buds are drilled with small holes, rose curculio (Merhynchites bicolor) may be the culprit. A weevil, it chews into buds to feed or lay eggs. Larvae gnaw the bloom as they develop, then drop to the ground to pupate. When disturbed, the curculio plays dead, dropping off the plant to avoid capture. Use this against them by knocking the bugs into a bowl of soapy water. Snip and remove infested flowers to keep larvae from developing.
  • Droopy blooms, distorted flowers or buds failing to open are indications of rose midge (Dasineura rhodophaga). Insects slice young tissue around new leaves or buds. Midges emerge in April from the soil. They require less than four weeks to grow from egg to adult and five generations or more can develop over aphidssummer.
    Bare root stock helps prevent the spread of rose midge. To control midge, clip off and destroy all infected buds, or treat with imidicloprid (Bayer Shrub & Tree Insect Control).
  • Aphids (Macrosiphum rosae) are a yearly problem, coating plants in shiny, sticky honeydew. Look closely at buds and new growth for these soft bodiedinsects.
    A strong jet of water hoses them off the plant to the ground, where poor eyesight and broken legs prevent them from finding their way back again. Severe infestations can be controlled with insecticidal soap.
  • When mysterious brown flecks scar the flowers and leave them looking spent before they open, suspect thrips (Frankliniella spp.). These small insects feed thripson cells one by one, leaving a silver trail across the flower. Often confused with heat damage, roses may be deformed if thrips attack as the budfirst shows color. Check for thrips by tapping the bloom over a white sheet of paper. If the specks that fall start moving around, you have them. Deadhead flowers to remove thrips but serious cases may require spraying with Spinosad, or imidicloprid (Bayer Shrub & Tree Insect Control).

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Updated Monday, February 24, 2014