The Colorado Noxious Weed Act (www.colorado.gov/ag/weeds) states that noxious weed management is the responsibility of local governing agencies: incorporated municipalities, counties, and lands owned by state and federal agencies. The Act states that the board of county commissioners of each county in the state shall adopt a noxious weed management plan for all the unincorporated lands within the county. The Larimer County Noxious Weed Management Plan was approved by the Board of County Commissioners on March 6, 2008. Enforcement procedures stipulated by the management plan are the responsibility of the Land Stewardship Manager under the County's Department of Natural Resources. Larimer County, in cooperation with the Colorado Department of Agriculture, Colorado State University Cooperative Extension, and other agencies, actively promotes compliance of the Noxious Weed Act. The County will enforce with the Act's provisions, on noncompliant landowners. For an interesting article on this topic see "Noxious Weeds and the Law."
The Larimer County Weed District emphasizes identification and management of the following 16 List B species, but reserves the right to enforce on any state-listed noxious weed if the infestation size and density deems it necessary. As mandated by the State Noxious Weed Act, the Larimer County Weed District also must eradicate all List A species (Click here to view the complete list). Photos and local information of the six known to exist in Larimer County can be found here: List A county information.
The following is a list of the troublesome weeds of Larimer County that the Weed District is frequently asked about, though these are not currently on the County Weed List.
Listed below are escaped ornamental species formerly available for purchase at nurseries, now on the state's prohibited sales list. These species have escaped to natural areas throughout Colorado and have demonstrated noxious weed characteristics. Other escaped ornamental species listed under the List A or List B species on the Larimer County Management Plan are: cypress spurge, dalmatian toadflax, dyer's woad, Mediterranean sage, myrtle spurge, purple loosestrife, tamarisk, teasel, and yellow toadflax.
The following 71 weed species are on the State's noxious weed list. The list is divided into categories by priority. The Colorado Department of Agriculture Website provides detailed information on identification and management of these species - www.colorado.gov/ag/weeds. Further information on specific descriptions, county locations, and management recommendations for highlighted species are given in this website.
List A species in Colorado that are designated by the Commissioner for eradication:
List B weed species are species for which the Commissioner, in consultation with the state noxious weed advisory committee, local governments, and other interested parties, develops and implements state noxious weed management plans designed to stop the continued spread of these species:
List C weed species are species for which the Commissioner, in consultation with the state noxious weed advisory committee, local governments, and other interested parties, will develop and implement state noxious weed management plans designed to support the efforts of local governing bodies to facilitate more effective integrated weed management on private and public lands. The goal of such plans will not be to stop the continued spread of these species but to provide additional education, research, and biological control resources to jurisdictions that choose to require management of List C species.
The following is a list of plants that the Weed District is asked about quite often for management recommendations or other advice. Some of the plants listed here are native and some are not. The information that follows each is based on our experience thus far, however; through collaborative research efforts and education, we hope to provide more information on each in the future.
Black medic (Medicago lupulina) - Black medic is a non-native member of the legume family with an annual or short-lived perennial life cycle. The plants are very low-growing with small yellow flowers. In areas where control is desired black medic can be controlled by Garlon, Milestone, Quicksilver, Transline, or Vista.
Broadleaf cattail (Typha latifolia) - Broadleaf cattail is a native perennial herb that thrives in marshy areas throughout Larimer County. Cattails reproduce by seed and rhizomes, and grow to 10 feet tall. Cattails can present a problem along ditches and roadsides. Selective control can provided by applications of Clearcast. Non-selective herbicides that provide control are Rodeo and Habitat.
Common cocklebur (Xanthium strumarium) - Common cocklebur is an annual of the sunflower family and native to the United States. Cocklebur grows to 4 feet tall, and by late summer produces spiny burs that can be a nuisance to livestock, pets and hikers. Cocklebur is a problem in farmland, run-down pastures, ditchbanks and abandoned fields. The most effective herbicides for control are Curtail, Milestone, Redeem, or dicamba + 2,4-D - product names Outlaw, Rangestar, Veteran 720, Weedmaster and others.
Dandelion (Taraxacum officinale) - Dandelion is a non-native perennial plant of the sunflower family. Dandelions produce a bright yellow flower that matures into a cottony seedhead that disperses windborne seed. Reproduction also occurs by way of shoots sprouting from the root crown. Dandelions are not typically considered a weed problem outside of turf areas, but can become a dominant plant in run-down pastures. Though palatable to livestock, dense infestations inhibit the growth of perennial grasses and other desirable species. Control of dandelions in range and pasture is best achieved by establishment of competitive grasses and applications of Curtail, Escort, Milestone, Redeem, Telar, Transline, Vista, or dicamba + 2,4-D pre-mixes of Outlaw, Rangestar, Veteran 720, Weedmaster, and others.
Foxtail barley (Hordeum jubatum) - Foxtail barley is a native perennial grass that reproduces by seed. Plants grow 1-2 feet tall and produce 2 inch long awns at maturity. Foxtail barley is tolerant of alkaline soils, and is an indicator plant of wet, poorly drained pasture areas. Such swales are often dominated by this grass which is palatable to livestock early in the season, but the awns of mature plants can be injurious to the mouth, throat, nose and eyes of livestock. There are currently no selective herbicides for controlling foxtail barley in pasture. Glyphosate (Roundup and others) can kill the plants, and would take out any desirable grasses as well. Tillage can be used to non-selectively take out infestations of foxtail barley. But even after re-seeding such areas with desirable pasture grasses, foxtail barley will eventually come back in if the soil remains poorly drained and saline conditions favor foxtail barley over other grasses.
Japanese knotweed (Polygonum cuspidatum) - Japanese knotweed is a shrubby, non-native perennial plant that can grow to 9 feet tall. Japanese knotweed was introduced into this country as an ornamental, but has escaped to become a major weed problem in natural areas of the Pacific Northwest and other parts of the United States. Not yet common in Larimer County, some plants have been identified and landowners are encouraged to eradicate this plant before it becomes a problem here.
Milkweed (Asclepias spp) - Showy milkweed is a native perennial frequently found in pastures and on roadsides in Larimer County. Plants grow to 5 feet tall, contain a milky latex, and produce large, spiny seedpods in late summer. Seed is dispersed in windborne clusters of cotton-like pappus. The densest infestations of milkweed typically occur on poorly drained sites due to the plant's tolerance of alkaline soils. Though not palatable, milkweed is toxic to livestock. In areas where control is desired, applications of Tordon or dicamba (Vanquish, Banvel, Clarity) can provide selective control.
Pigweed (Amaranthus spp) - Pigweed species most common in Larimer County are redroot, tumble and prostrate pigweed. These species are non-native annuals that germinate in May and set seed by August. Pigweed is a problem primarily in crop production, but can be found in abandoned fields and run-down pastures. The most effective herbicides for control are Milestone, Telar, Vista or dicamba + 2,4-D - product names Outlaw, Rangestar, Veteran 720, Weedmaster and others.
Poison ivy (Toxicodendron rydbergii) - Poison ivy is a native perennial vine-shrub that can be found in a variety of habitats in Larimer County. The leaflets are arranged in characteristic groups of 3 and often have reddish coloration and tend to droop. Because of the toxic residue that causes severe skin rash, poison ivy is seldom a desirable plant. Best products for control are dicamba (Banvel, Clarity, Vanquish), Garlon, Milestone, and Redeem.
Prickly lettuce (Lactuca serriola) - Prickly lettuce is a non-native biennial plant that can grow to 5 feet tall. Prickly lettuce grows from a taproot, producing small yellow flowers in mid-summer. The stems contain a milky juice. At maturity the seeds disperse in puffballs, much like a dandelion. Prickly lettuce is an invader of abandoned fields, roadsides and run-down pastures. Best control provided by applications of Escort, dicamba (Banvel, Clarity, Vanquish), Garlon, Milestone, Redeem, Vista, Telar, or Transline.
Rabbitbrush (Chrysothamnus nauseosus) - Rabbitbrush is a common name for 12 species in the western United States. The species most common in Larimer County is gray or rubber rabbitbrush. This native perennial shrub can grow to 4 feet tall, thriving on dry sites. Unpalatable to horses and cattle, rabbitbrush can dominate over-utilized pastures. Controlling rabbitbrush is difficult. Spot-spraying individual plants with a non-selective herbicide, such as Arsenal, is most effective.
Ragweed (Ambrosia artemisiifolia) - Ragweed species common in Colorado are western and giant ragweed. Western ragweed is most common in Larimer County. These plants are native annuals that produce a pollen causing hay fever. Ragweed is not highly competitive or invasive. In areas where control is desired, applications of Curtail, Milestone, Redeem, Vista, or dicamba + 2,4-D - product names Outlaw, Rangestar, Veteran 720, Weedmaster and others.
Redstem filaree (Erodium cicutarium) - Redstem filaree is a non-native, low-growing forb of the geranium family. This plant typically follows a winter annual life cycle; germinates in the fall, over-winters as a rosette and produces showy purple-lavender flowers in the spring/summer. After flowering, the plants produce a long thorny seed head, which gives this plant it's other name, storksbill. The seed heads are considered a nuisance and can be aggravating to livestock. Redstem filaree typically completes it's life cycle by mid-summer, dries up and is not noticeable again till the following spring. Redstem filaree is controlled by Escort, Plateau and Telar. Most infestations are not dense enough to warrant an herbicide application. A healthy stand of grass easily out-competes this low-growing forb and keeps redstem filaree populations down to a minor nuisance.
Rye (Secale cereale) - Rye is a cereal crop that has escaped into natural areas, pastures and roadsides and become a weedy species. Referred to as feral rye or volunteer rye, this grass is highly competitive and difficult to control. The life cycle of feral rye is the same as cheatgrass, winter wheat, and other species known as 'winter annuals'. This cycle begins with germination in late summer or early fall (some spring germination can occur as well), over-wintering as a green grass, and resumption of growth in the spring. Winter annuals set seed and complete their life cycle by mid-summer. Feral rye has grazing value in the spring, but the invasive character of this grass over-rides such value. If left unchecked, feral rye can dominate the plant community and is a wildfire hazard. Most effective control is Landmark or Oust (read label carefully for application within appropriate areas) or an application of glyphosate (Roundup and other brand names) at a rate and timing that is not injurious to desirable perennial grasses. Other selective herbicides are being investigated by Colorado State University and the Larimer County Weed District. Recommendations are available yet best practice would be to set up a site visit with a Weed Specialist to insure best management.
Smooth brome (Bromus inermis) - Smooth brome is a non-native perennial grass commonly utilized for hay and forage production in Larimer County. Smooth brome is a sod-forming plant that, once established, is extremely competitive and is often found in pure stands. Smooth brome's competitive ability and invasiveness has made this grass undesirable in areas where establishment of a native plant community is desired. Control is difficult and may require 2 or more applications of glyphosate (Roundup and others). In some cases, moldboard plowing, or complete turnover of the soil to disrupt the extensive underground root system is necessary, in addition to glyphosate applications.
Sunflower (Helianthus spp) - Sunflower species common in Larimer County are prairie sunflower and common sunflower. These native annuals can grow to 10 feet tall under favorable conditions. In situations where dense stands of sunflower are undesirable, control can be attained by applications of dicamba (Banvel, Clarity, Vanquish), Escort, Milestone, Redeem, Telar, or Vista.
Western salsify (Tragopogon dubius) - Western salsify is a non-native biennial of the sunflower family. The plant has long, narrow leaves and a milky juice. Western salsify produces bright yellow flowers early to mid-summer, followed by mature puffball seedheads similar in appearance to dandelions. This forb grows 1-2 feet tall and is most common on disturbed sites and neglected pastures. A vigorous stand of grass will keep this plant in check. In situations where western salsify populations are dense enough to be a problem, control can be achieved with an herbicide application of dicamba + 2,4-D - product names Outlaw, Rangestar, Veteran 720, Weedmaster and others.
White locoweed (Oxytropis sericea) - White locoweed also known as silky crazyweed, is a native perennial plant of the legume family and is common on western rangeland. White locoweed produces white flowers and contains a compound called swainsonine, which is toxic to all livestock. Locoweed can be controlled by Escort, Tordon, and Transline.
Yellow sweetclover (Melilotus officinalis) - Yellow sweetclover is a non-native plant of the legume family that grows to 6 feet tall. This alfalfa-like plant has an annual or biennial life cycle, producing a profusion of yellow flowers by mid-summer. Yellow sweetclover was introduced into Larimer County for roadside restoration, but is no longer utilized for that purpose. Occurrence appears to be affected by moisture patterns, some years sweetclover seems to be everywhere, other years not much can be found. Yellow sweetclover is not often a desirable species due to a 'stemy' growth habit, invasiveness in certain situations, and potential to cause bloat in cattle. Landowners wishing to control sweetclover should apply a tank mix of Milestone + 2,4-D, or Milestone + Escort (brand name - Chaparral).
Yucca (Yucca glauca) - Yucca is a native perennial plant found on dry, sandy sites. Also referred to as soapweed yucca, these succulent plants grow to 4 feet tall with long, stiff pointed leaves. The flower pods are highly palatable to wildlife and livestock. On run-down rangeland yucca may become dense enough to be undesirable. Herbicides labeled for control are Velpar and Chaparral (pre mix of Milestone and Escort).