Weeds are spreading rapidly on Colorado rangeland and in pastures and natural areas. Manage weeds during the current growing season to decrease or prevent future infestations. All too often, weed control during a growing season is evaluated in terms of financial return only for that season and not for future impact. All weed management must be applied and evaluated over an extended time to be successful.
Be persistent in weed management, particularly with perennial weeds. Most successful weed management systems require input for several growing seasons. Weed infestations occur over time and seldom can be cured in a single growing season. Soil seed dormancy of most weeds and the extensive root systems of creeping perennials requires that weed management systems in rangeland, pasture and natural areas need to be designed for input over extended time periods. Weeds to be watchful of in our area include:
Canada Thistle. It is an aggressive, creeping perennial weed that infests crops, pastures, rangeland, roadsides and noncrop areas. Generally, infestations start on disturbed ground, including ditch banks, overgrazed pastures, tilled fields or abandoned sites. Canada thistle reduces forage consumption in pastures and rangeland because cattle typically will not graze near infestations. CSU research shows that under habitat conditions where the root growth of Canada thistle may be restricted, such as high water tables, mowing is advantageous. The key to controlling Canada thistle and other perennials is to exhaust root nutrient stores, regardless of the control procedure used. Canada thistle is difficult to control and may recover.
Leafy Spurge. It is a creeping, herbaceous perennial weed of foreign origin that reproduces from seed and vegetative root buds. It can reduce rangeland cattle carrying capacity by 50 to 75 percent. About half of this loss is from decreased grass production. Cattle won’t graze in dense leafy spurge stands and these areas are a 100 percent loss to producers. Sheep or goats can graze leafy spurge. This stresses the weed and relieves grasses from competition so pastures can be used effectively by cattle and horses. Sheep or goat grazing may make leafy spurge more susceptible to fall-applied herbicides. Leafy spurge is a persistent, hard-to-control weed that often recovers from control attempts.
Musk Thistle. A biennial. The key to successful management is to prevent seed formation. Musk thistle occurs in pastures in direct proportion to moisture and sunlight. The weed grows more in pastures in poor condition than those in good condition. Reseeding once its populations are reduced, may be a necessary final management step to prevent reinfestation by musk thistle. Cut off the weed below the soil line with a hoe or shovel before the bud stage or treat the weed in spring or fall with herbicides.
Diffuse Knapweed. A short-lived perennial, biennial, or occasionally an annual. The key to management is to prevent it from going to seed. Diffuse knapweed invades overgrazed pastures, forms dense stands and may be toxic to horses. After an herbicide treatment, reseed a poor-conditioned pasture so grasses can be present to compete with surviving diffuse knapweed and prevent re-invasion by the weed.
Prevention is the first line of defense and keeps weeds from occurring or increasing in an area. Preventive techniques include planting high quality, weed-seed-free crops or grass seed. Legislative items, such as clean-seed acts and weed-management laws, also can help stop weed problems before they occur or may deter weed spread. An important preventive measure related to control is to keep weeds from going to seed. This is important for annuals and biennials, because that is the only way they reproduce. Perennials reproduce from seed, as well as vegetatively from their root systems. Annual weeds live for one growing season, biennials for two and perennials more than two. However, preventing seed set is extremely important to keep perennials from starting new infestations some distance from existing ones.
Eradication is the removal of weeds from an area so they will not recur unless reintroduced. If eradication creates an open area, one weed problem may be cured simply to create another one. If eradication is necessary, revegetate the ground to prevent another weed infestation. Eradication is desirable for small patches, 10 to 100 feet in diameter, but not always for larger ones.
Control, the most common management strategy, reduces a weed population to a level where you can make a living off of or enjoy using the land. Adequate control also may prevent future infestations. There are four control methods: cultural, mechanical, biological and chemical.
• Cultural control methods promote growth of desirable plants. Seeding is the most commonly used cultural control method and must be combined with control methods that decrease the target weed population and gives the seeded species an opening in the environment to successfully germinate and establish (colonize). The USDA-Natural Resource Conservation Service is an outstanding source of information as to what species to plant in a particular area and at what rate. Fertilization, irrigation and planting at optimum densities let crops compete with weeds and not with each other. While nitrogen fertilization increases yields in grass hay meadows, it also fosters weed establishment and growth. Fertilize cautiously, especially with nitrogen, and only when necessary as determined by soil testing.
• Mechanical control methods physically disrupt weed growth. This is the oldest control method and is used most often worldwide. Tillage, hoeing, hand-pulling, mowing and burning are examples. To mulch or smother weeds often is considered mechanical, even though it simply excludes light rather than physically disrupting weed growth.
• Biological control methods use an organism to disrupt weed growth. Often the organism is an insect or disease and a natural enemy of the weed. This is called classical biological control. Classical is not the only form of biological control. Livestock can be effective weed-management tools if used correctly. However, improper livestock management (overgrazing) can be extremely damaging to the environment and exacerbate weed problems.
• Chemical control methods use herbicides to disrupt weed growth. The first rule of any pesticide use is to read the label before using the product and follow all directions and precautions. (NOTE: Avoid using soil-active herbicides, such as Tordon, Banvel/Vanquish/Clarity, or Telar, near windbreak plantings and other desirable woody vegetation. Plant injury or death can occur. Do not allow any herbicide to drift onto woody or other desirable vegetation for the same reason.)
A weed management system uses two or more control methods. The key is to encourage desirable plant growth with optimum fertilization, when necessary, and/or irrigation. Plant competition is an often overlooked tool and should be used first, but not exclusively. When enhancement of the desirable plant community is necessary, make sure you seed at optimum rates to ensure establishment and subsequent competition with weeds. Generally, perennial, sod-forming grasses compete best with weeds. Till, hoe, hand-pull, mow or mulch (mechanical control) if desired. Herbicides (chemical control) are powerful tools that should be used judiciously, not exclusively. Unfortunately, too often herbicides are used to make up for poor cultural or mechanical management decisions. Herbicides may be a component of the weed-management system. Biological controls can also be part of a system. Several natural enemies currently are available from the Colorado Department of Agriculture. Livestock grazing can be effective, depending on the weed species, if the livestock are properly managed for weed control.
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Youth ages 8 to 13, mark your calendars now for Fun in the Sun Day Camp sponsored by Archuleta County 4-H. Our 2009 camp will take place Monday, June 15, through Friday, June 20, from 9 a.m. to 3 p.m. If you would like to be included in our Fun in the Sun mailing list, call Sandy at 264-5931 or e-mail her at email@example.com.
May 15 — 1:45 p.m., Cloverbuds.
May 15 — 2 p.m., Rabbit project.
May 15 — 3 p.m., Turkey project.
May 15 — 3:45 p.m., Poultry project.
May 16 — 8 a.m., 4-H Livestock weigh-in.
May 16 — 10 a.m., Photography project.
May 16 — 10 a.m., Dog Agility and Obedience project.
May 18 — 4 p.m., Sewing project.
May 18 — 6 p.m., Lamb project.
May 18 — 6:30 p.m., Backcountry Horsemen meeting.
May 19 — 4 p.m., Entomology project.
May 19 — 6 p.m., 4-H Council meeting.
May 20 — 4 p.m., Sportsfishing project.
May 20 — 6 p.m., Fair Board meeting.