Weeds: Butterfly bush – Buddleja davidii

• Family: Scrophulariaceae
• Cycle: Perennial
• Plant type: Broadleaf

Biology

Butterfly bush, Buddleja davidii, is a deciduous shrub that grows from 3 to 15 ft tall. Until only recently, this species was celebrated for its robust growth, fragrance and range of bloom colors, and often recommended for its ability to grow in poor soil and to attract butterflies. Unfortunately, the butterfly bush, Buddleja davidii, is now considered an invasive species. Flowers bloom between mid-summer and the first frost in Washington State. These flowers have 4 petals and can be purple, white or pink. The flowers produce high quantities of nectar and are attractive to butterflies, hence the common name. Butterfly bush is a prolific seed producer; a single flower cluster can produce over 40,000 seeds. Seeds are dispersed by wind and water and may remain dormant in the soil for many years. New plants can even establish from cuttings. These shrubs also alter the nitrogen and phosphorous amounts in the soil, giving it an advantage that displaces native species, particularly in riparian areas. In forests, it competes with Douglas-fir tree seedlings. Butterfly bush was added to the Washington State Noxious Weed list in 2006. In Oregon, the ODA (Oregon’s Department of Agriculture) officially classified it as a class “B” noxious weed in 2004. In addition to ODA’s “B” noxious weed listing, Buddleja davidii appears on the “Most Invasive” species list of the Pacific Northwest Exotic Pest Plant Council and the Native Plant Societies of Oregon and Washington. The OSU Extension Service Master Gardener Program no longer recommends it for butterfly gardens because of its invasiveness. Both OSU and ODA scientists are encouraging home gardeners to pay close attention to choosing butterfly bushes that are cultivated varieties, not the straight wild species, Buddleia davidii. Only this species, Buddleia davidii, not specially bred cultivars are subject to Oregon’s noxious weed listing. Many seedless varieties have been developed for home gardens. A few native and ornamental alternatives to use other than planting the butterfly bush include varieties such as; Lewis’s Mock Orange, Red-flowering Currant, Black Chokeberry, Meyer Lilac or California Lilac.

Habitat

Spreading rapidly by windblown seed, butterfly bush displaces native vegetation in disturbed, open areas and along coastal forest edges, roadsides and especially on sunny stream sides and riverbanks. Along riversides it can develop roots on branches that have been buried or broken off. Although butterflies will use this plant as a nectar source their larvae cannot survive on it. By replacing native larval food source plants butterfly bush can have a negative impact on wildlife.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Removal of butterfly bush is best when it first comes into flower but has not yet produced seeds. Small plants can be easily hand-pulled when the soil is moist. Remove larger bushes by cutting the plant at the base. Dig up the stump and cover it with a thick plastic bag, or mulch to prevent regeneration. Remove new shoots until the rootstock dies, and do not leave stems on the ground, or they may root.
• Don’t let Buddleia go to seed. Deadhead, or clip off all flower heads in the fall. Do not wait until spring.
• Do not leave the clippings on the ground, as they can easily take root and create a new plant. Dispose of plants by sending away in your yard debris pickup service, where it will be ground up and composted. Whatever you do, don’t dump the clippings along a roadside or along a creek or river, as these are preferred habitats for escaped butterfly bush.
• Watch your property for new seedlings. Dig up and get rid of any volunteer bushes. Don’t give them away to friends.
• To control butterfly bush, without killing the plant, the shrub can be pruned back severely in the fall. This will produce a smaller, more compact plant in the spring. Flowers, then, will be more accessible, allowing them to be removed after flowering. If flowers are being removed from the plant after the flowers have dried, it is best to put a plastic bag over the flower before it is cut, to catch any falling seeds.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• Controlling butterfly bush by spraying with a brush-control herbicide is somewhat effective. But for better results, cut the trunk off at the base and apply concentrated glyphosate or triclopyr to the freshly cut surface.
• For more detailed information on the cut stump treatment method and more information on using herbicides to control weeds in different crops and locations, please see the Pacific Northwest Weed Management Handbook.
• Always follow the label directions on any herbicide product you use to minimize any potential risks to you and the environment and follow all applicable laws and regulations regarding herbicide use on your site.
• Contact the Noxious Weed Program if you are unsure about what to do. (Source: kingcounty.gov)