Rush Skeletonweed

Growth Characteristics: Rush skeletonweed was introduced from southern Europe. It grows 1 – 4 feet tall, and flowers in mid-summer through fall. It reproduces by seed, by root fragments, and by spreading vegetatively.

Flowers: Bright yellow, strap-shaped flowers in the axils or at the ends of branches. The flowers are often found in groups of 2 to 5 flowerheads, each with 9 to 12 flowers. Mature, healthy plants can produce 1,500 flower heads, and up to 20,000 seeds.

Fruits/Seeds: Pale to dark brown ribbed achene, with a slender beak at the top, bearing a soft, white plume of fine hairs which allow it to travel long distances by wind.

Leaves: Basal rosette leaves are lance-shaped, shallow lobed, with a pointed terminal lobe and lateral lobes opposite and usually pointing backward toward the leaf base. They are similar in appearance to those of dandelions. The stem leaves are bract-like, and are often lacking. When they do occur, stem leaves are small and linear, 0.8 to 4 inches long, and deciduous. The leaves are glabrous, often showing tinges of reddish-brown, and are usually darker in color than other species which may look similar.

Stems: Wiry branched flower stems. The lower stems have dense, brown, bristly, downward pointing hairs. Milky sap throughout.

Roots: A distinctive long, thin taproot which can be 14 inches deep when a seedling is only a few inches across and over 6 feet deep at maturity. Rush skeletonweed also has lateral roots, especially when growing in sandy or gravelly soils. New plants can arise from broken root fragments.

Rush skeletonweed is found along railroads, roadsides, fields, waste places, and disturbed ground. Areas of road and rail fill and other areas of artificial gravel substrate are particularly susceptible to infestation. It is not tolerant of shade or extremely dry conditions. Because of its deep and extensive root system, rush skeletonweed plants are likely to survive severe fire, sprouting from any part of the remaining root system.

Soils: Most commonly found on either extremely shallow soils over bedrock, or coarse-textured, deep, well-drained soils. Fine-textured soils appear to impede rush skeletonweed root development and regeneration by buds on lateral roots.

Although Rush skeletonweed is not a state declared noxious weed in Utah at this time, the proximity of infestations in Idaho and Nevada, as well as some isolated occurrences in Utah, requires land managers to be alert to the possibility of infestations so they can be controlled quickly. There are three forms of rush skeletonweed in the

U.S.

, each differing in the morphology of their inflorescence and the susceptibility to control methods. Determining which form is present in an infestation is important when determining a plan for control.

Rush skeletonweed rosette leaves are palatable to cattle and wildlife, so small amounts in rangeland are not considered problematic. The more serious problem occurs on overgrazed sites, and those disturbed by off-road vehicles or other means. On these sites, rush skeletonweed is likely to become the dominant herbaceous species. It often invades disturbed open-canopied forest, logged, and burned areas.

There appears to be no single control method which is effective for rush skeletonweed, rather a combination of control methods seems to be needed to gain control over infestations. Control methods include physical, mechanical, chemical, and biological.

Small infestations can be eradicated with diligent effort using physical and/or chemical treatments. Once established, rush skeletonweed is extremely difficult to control using herbicides alone, primarily due to the difficulty of translocating herbicides into its extensive root system. Degree of translocation of herbicides depends on environmental conditions, type of herbicide used, and physiological status of the plant.

There is some evidence that areas with vigorous native vegetation are resistant to rush skeletonweed invasion.

Rush Skeletonweed (Chondrilla juncea). Photo courtesy of Utah State University Archive, Utah State University, Bugwood.org