WSU CAHNRS

CAHNRS and WSU Extension

Wheat and Small Grains

Rush Skeletonweed

Also Known As

Gum Succory, Devil’s Grass

Description

Rush SkeletonweedRush Skeletonweed, Chondrilla juncea L., originated from Eurasia and belongs to the sunflower family. Rush skeletonweed was first identified in the Pacific Northwest from Spokane County, Washington in 1938. This species is a stoutly taprooted perennial, reaching heights between 1 and 4 feet at maturity. Stems are slender and generally smooth, except on the base which exhibits course, downward bent hairs (distinguishing characteristic). Alternating leaves are inconspicuous; early stage rosettes resemble that of a dandelion. Scattered flowerheads are present from July to the first frost. Flowerheads retain yellow flowers; petals are flat across the end and distinctly toothed. This vigorous weed regenerates through seeds as well as lateral root segments. An average of 1500 flowerheads is produced per plant each with (usually) 10-12 flowers. Each flower produces one seed so seed production can be as high as 15,000 seeds annually. Each seed has a tuft of fine hairs which aids in its dispersal via wind. Damaged leaves and stems secrete milky white latex. Once established, rush skeletonweed can reduce crop yields by as much as 70 percent. The high fibre content and milky juice in the stems also greatly hamper harvest and tillage operations. Rush skeletonweed infiltrates roadsides, waste areas, disturbed soil, wheat and farm land. Infestations can occur in areas receiving less than 10 inches to areas with more than 60 inches of precipitation.

Distribution: Western Whitman County is heavily infested with rush skeletonweed, primarily in the range and scablands. Large infestations perforate the banks of the Snake River. Other counties have rush skeletonweed scattered throughout.

Control Methods

Rush skeletonweed is difficult to control. Prevent plants from going to seed. Cut or pull isolated plants before flowering. If flowering has occurred, bag and remove plants for burning.

Mechanical: Repeated mowing (mechanical control) is effective only before flowering. Its extensive root system and regenerative ability prevent control by tilling and/or cultivation. When rush skeletonweed is mechanically injured, shoots can form from any part of the main root, from the lateral roots, and from root fragments at least four feet deep.

Chemical: Early spring application with 2,4-D; picloram; 2,4-D + picloram; clopyralid; or clopyralid+dicamba, to rosettes achieve adequate control.

Biological: Biological control agents such as the gall midge (Cytiphora chmidti), a gall mite (Eriophyes chondrillae), and a rust fungus (Puccinia chondrillina) have proven effective. Another insect that may soon be available for the control of rush skeletonweed is the root moth (Bradyrrhoa gilveolella).

Because no single treatment provides long-term control of rush skeletonweed, an integrated strategy must be adopted. The first line of defense is to prevent introductions of the weed. Once the weed becomes established, integrate combinations of competitive plantings, crop-pasture rotations, sheep grazing, biological control agents, and herbicides should be used to reduce rush skeletonweed to manageable levels.

Resources

Wheat and Small Grains, P.O. Box 646420 Washington State University, Pullman, WA 99164-6420, 509-335-1719, Contact Us
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