Walla Walla County Extension

Weed of the Month

Rush Skeletonweed

Rush skeletonweed (Chondrilla juncea) an introduced species from Eurasia, is a perennial in the Sunflower family. One rush skeletonweed plant can colonize an entire area by producing satellite plants from lateral root formation. It ranges from one to four feet tall, with a taproot reaching down seven feet, or more. The sharp, deeply toothed, basal leaves of the rosette resemble a dandelion but as the flower stems elongate in early summer, red hairs bend downward on the lower 4 to 6 inches of the stem and the basal leaves wither. The remainder of the stem is relatively hair-free and smooth with occasional narrow leaves that are inconspicuous, giving the plant a skeletal appearance. Both stems and leaves exude milky sap when cut.

Flowering and seed production occur from mid-July through frost. Yellow ¾-inch flower heads are widely scattered along the stems in the leaf axils or at the branch tips, found singly or in clusters of two to five. Flower petals number from 7-15 and are squared across the end with tiny teeth. Each rush skeletonweed plant can produce up to 20,000 seeds. Seeds are light brown to black, ribbed, and have white bristles at one end so that they are easily spread by wind.

Rush skeletonweed prefers well-drained, light textured soils along roadsides and in rangelands, grain fields, and pastures. The extensive and deep root system makes control difficult. Cultivation spreads the weed due to shoot growth from any root fragments up to four feet deep. Grazing can inhibit seed production. Sheep will graze the rosette and early flowering plant and cattle will also graze the tips of flowering stems early in the season.

Control with herbicides requires an aggressive follow-up program with repeated applications.

• Picloram (Tordon) applied just before or during bolting from late fall to early spring is the most effective treatment currently available.
• 2,4-D or MCPA applied to rosettes in spring immediately before or during bolting will inhibit aboveground growth but will not prevent new plant development from root buds.
• Clopyralid (Transline, Stinger) is applied to rosette in fall or up to early bolting in spring. However, this product will injure or kill sensitive broadleaf forages and may injure certain crops for several years after application.
  BE SURE TO FOLLOW ALL PESTICIDE LABEL INSTRUCTIONS AND PRECAUTIONS.

The biological control agents are very specific to plant biotypes, making long term biocontrol programs difficult to manage.

• The gall midge larva, Cystiphora schmidti, feeds on the leaf or stem tissues where eggs have been laid. Feeding activity initiates gall formation which is characterized by a swelling and yellowish to maroon discoloration of affected tissue.
• A rust fungus, Puccinia chondrillina, causes development of rust brown pustules surrounded by yellow tissue on stem and leaves. Plants have reduced growth, vigor, and reproductive potential and infected seedlings may be killed.
• The gall mite, Eriophyes chondrillae, is considered the most effective biological control agent available, to date. This mite feeds on developing vegetative and flower buds and stunts the plant, decreases or completely prevents seed production, and commonly results in death of seedlings or first-year satellite plants.