Umatilla County
Most Wanted Weed
Most Popular
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Location
Umatilla County Weed Control
3920 Westgate Street
Pendleton, Or 97801
Info:541-278-5462 Fax: 541-278-5402
dand@co.umatilla.or.us
The Weed Department is open 6:30 am. to 5 pm. Mon. through Thr.
Location and hours for other County offices
Most Wanted Noxious Weed "Rush Skeleton Weed"
Description and
VariationDescription and Variation: Rush skeletonweed
belongs to the chicory tribe of the sunflower family. This herbaceous
perennial ranges from one to four feet tall, with a taproot reaching
down seven feet, or more. The seedlings have a long thin taproot. Rush
skeletonweed overwinters as a rosette of hairless, basal leaves that
are two to five inches long and ½ to 2 inches wide and broader
at the tip. The lateral lobes point back toward the base - very similar
to a dandelion. The mature plant consists of a dark green, nearly
leafless flowering stem, with many aerial branches. The basal rosette
is absent at this stage. The stem and aerial branches support a few
leaves, which are narrow and linear, and 
mostly entire. A
distinguishing characteristic of rush skeletonweed is the presence of
coarse, downward pointing brown hairs near the base of the stem. The
stems and roots of rush skeletonweed exude a white latex sap when cut.
The flower heads, about ½ inch in diameter, grow along the stem
in the leaf axil or at the branch tips, and they are found individually
or in clusters of twi to five. Each flower head has 7-15 (usually 11)
ray flowers, with yellow ligules resembling petals. These yellow
ligules are strap shaped with small teeth across the blunt end. Mature,
vigorous plants can produce 1,500 flower heads, with the capability of
producing 20,000 seeds. The immature seeds are greenish-white, and they
gradually darken to a yellow-brown or olive-green in the 13-15 days it
takes to mature. The seed color can be used as an indication of
maturity, with light colored seeds showing low germination rates (Old
1981). Each seed has a pappus, which is capable of carrying seeds along
wind currents up to 20 miles (Cuthbertson 1967 and Schirman and
Robocker 1967 as cited in McLellan 1991).
Detrimental: Rush
skeletonweed is a threat to irrigated lands of
the Columbia Basin, to the sandy soils of dry land wheat areas (Old
1981), and
it is a threat to
rangelands. Rangeland infestations impact
the cattle industry when rush skeletonweed displaces native or
beneficial forage species grazed by livestock and wildlife. Forage
production is lowered when rush skeletonweed successfully outcompetes
beneficial species for limited resources, particularly nitrogen. Often,
the cost of herbicide control is not economical due to low productivity
of the land (Sheley).
Rush skeletonweed spreads
from rangeland to croplands by seed. Once
established on roadsides adjacent to croplands, mechanical injury to
the plant can produce shoots from any part of the main root, from the
lateral roots, and from root fragments at least 4 feet deep (Old 1981).
Once established in wheat-fallow systems, cu
ltivation is the
major
factor of spread. Crop yields are also reduced as a result of rush
skeleton-weed outcompeting grain for soil moisture and nitrogen. Grain
harvest is difficult because of the wiry stems, and the latex sap of
rush skeletonweed gums up harvesting machinery. In Australia, crop
yields were reduced by 50-70 percent, with some fields later converted
to rangeland.