Three kinds of invasive weeds have emerged in Rio Blanco County along Hwy. 13. Leafy spurge (left), musk thistles (center) and white top (right) are all being quite (ob)noxious.
BY LINDA MASTERS AND JANE TURNBURKE
Special to the Herald Times
RBC | Several people have been reporting the spread of thistles and other weeds along the State Hwy 13 right-of-way and adjacent private and public lands in Rio Blanco County. Of real concern is the spread of a legal class of “List B” noxious weeds. Colorado “List B” noxious weeds are designated by the state for mandatory control in regions where they are not yet widespread and where prevention of new infestations in these areas is the primary goal.
On State Hwy 13 south of Meeker, the presence of musk thistle, a “List B” weed, is increasing along state road easements and adjacent rangelands and private pastures. Musk Thistle is a non-native aggressive biennial weed. It produces from seed usually as a biennial, meaning that in its first year it only produces a flat rosette. The second year, it sends up one main and several lateral shoots and may produce 100 or more flowering heads that can then produce 20,000 seeds. Luckily only about 1/3 of these are viable. Still this plant is a very prolific seed producer flowering over a seven- to nine-week period and even blooming again in the fall. Seed dispersal methods include animals, farm machinery, cars, road construction equipment and failure to clean heavy equipment between project sites.
what makes it a NOXIOUS WEED?
A noxious weed is any invasive, non-native plant that threatens local agriculture, ecosystems, or wildlife habitat.
CONTROL
Maintaining rangelands and pastures in good condition is important for control of musk thistle so that desirable plant species have a chance to compete with weeds. Musk thistle thrives in soils disturbed by heavy equipment used during road constructions and other disturbances such as heavy use by livestock and recent drought conditions that add to stressed range conditions. Weeds starting from these disturbances should be addressed immediately and not allowed to spread from their initial sites onto neighboring land. If not controlled, expensive multi-year treatments are necessary to contain the situation. The recent, extensive, multi-year road construction has definitely disturbed the Hwy. 13 roadsides. State Highway departments usually spray herbicides along these areas following large disturbances during construction. It is not clear to this writer if that has occurred along Hwy. 13. Weed control follow-up by the state are usually part of the construction contract so that large weed infestations do not occur.
Since Musk Thistle reproduces by seed, the use of herbicide to control musk thistle is effective when used correctly to prevent viable seed production. Other herbicides are formulated to be applied to the thistle rosette. Click here for more information and a list of herbicides.
Biologic control is also an option. There are two weevils that will kill the musk thistle. The Colorado Department of Agriculture has developed a weevil that attacks the crown of the musk thistle rosette and kills or weakens the plant in the rosette stage. It is currently being distributed throughout Colorado. A request has been made to the Palisade Insectary by the RBC Extension Office to be put on the waitlist to receive crown weevils as soon as they are available. A less effective weevil, the “seed head weevil” can already be found throughout Colorado. This one lays its eggs on the back of developing flowers. More information is available in the above-referenced Fact Sheets. Combining the use of biological control with herbicides requires appropriate timing but can be extremely effective.
MORE WEED PROBLEMS
North of Meeker, two other “List B” weeds are spreading alongside Hwy. 13. These are Leafy Spurge, which has very distinctive greenish-yellow flowers, and White Top, which has tightly packed white flowers that make up a compact head. Both of these will out-compete more desirable plant species, especially in disturbed ground such as roadsides and adjacent lands. They are both non-native, very aggressive, perennial weeds that, once established, are very hard to control and eradicate. Leafy Spurge spreads by seed and also by extensive creeping roots that can extend up to 30 feet producing new shoots and roots. A specific flea beetle can be an effective control, especially when combined with grazing (sheep and goats) and/or herbicides. Rio Blanco County has also been put on the waitlist at the Palisade Insectary to receive these insects. For more information call Linda Masters at the Extension office at 970-878-9494 or click here.
White Top (aka Hoary Cress) is a “List B” perennial mustard. The key to cost-effective control of white top is preventing its establishment through use of weed-free hay, cleaning of road construction equipment and early detection of small infestations. Aggressive management and active plans for eradication should be acted on immediately before this weed is allowed to spread. Once established it is very hard to control. There is no biological control for this weed at this time. For more information on this weed click here. If you have additional questions regarding weeds or weed control contact Linda Masters at the RBC Extension Office at 970-878-9494 or Jane Turnburke at the RBC Weed and Pest Department at 970-878-9672.
All these plus knapweed are infesting Tschuddi Gulch.Knapweed is extemely hard to control once it gets a foothold. This is wintering area for our deer and elk.It’s important that this problem is addressed.