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Noxious Weeds & Invasive Species

BLM NEVADA'S WAR AGAINST WEEDSInvasive species can be hazardous to public lands and waters! Prevent their introduction and spread by cleaning your vehicles, machinery, and boats.

Maintaining or restoring land health is one of BLM’s highest priorities. Among the obstacles to maintaining healthy lands and restoring impaired ecosystems are noxious and invasive weeds. These plants dominate many sites, can cause long term damage to plant communities, and degrade resource values.

In the Great Basin, Mohave Desert, and other parts of the intermountain west BLM’s "War Against Weeds" now has two parts. The rapid spread of noxious weeds on western range and forest lands over the past half century has been well documented. The other part of the “War Against Weeds” is non-native invasive annual grasses, i.e., cheatgrass, medusahead, red brome, and others. Based on satellite imagery from 2003, about 11 million of the almost 48 million acres of BLM Nevada lands had at least 10% cover of cheatgrass and other annual grasses. While this may not seem like much, when such areas burn, the cheatgrass can be released, greatly increasing in coverage, initiating a cheatgrass fire cycle, and ecologically dominating that site. There are some important differences between the noxious weed and invasive annual grass problems.

Noxious weed is a legal and regulatory designation. The BLM defines a noxious weed as: "A plant that interferes with management objectives for a given area of land at a given point in time." Nevada Revised Statute (NRS) 555.005, says noxious weeds are: "… any species of plant which is, or is likely to be, detrimental or destructive and difficult to control or eradicate." In 2008, 47 species were on the Nevada Noxious Weed List, which is in Nevada Administrative Code (NAC) 555.010. The Nevada Noxious Weed List ( is updated from time to time. To date it has never gotten shorter. All of Nevada’s noxious weeds can be found somewhere on Nevada’s public land. So, in addition to BLM’s inherent stewardship concerns about noxious weeds we also have legal responsibilities.

Presently cheatgrass is by far the most problematic of the invasive annual grasses in Nevada. It is common and occurs throughout the state. Red brome is established in the Mohave Desert. Smaller infestations can be found in other parts of Nevada. Medusahead is moving into Nevada. Most infestations are still in the western and northern parts of the state on clayey soils. In Nevada medusahead is a Category B noxious weed, and the only one of the invasive annual grasses on the noxious weed list. Schismus spp. or Mediterranean grass is still mainly restricted to southern Nevada. Currently these are the problem non-native invasive annual grasses, but others will likely show up.

One problem with invasive annual grasses is the “annual grass fire cycle.” In years with weather favorable to cheatgrass, for example, it can fill in the natural open spaces between the native plants. If a fire starts it spreads easily through these continuous fuels and can get much bigger than without cheatgrass. Many native plant species recover slowly from burns, while cheatgrass is adapted to respond quickly to the open space and release of nitrogen and other nutrients following a burn. Native plant communities that once burned every 75 to maybe 250 years are now burning every five to ten years. Several repeated fires can remove many of the native species from the plant community. The resultant plant communities are much simpler with fewer resource and habitat values. Currently the impacts from these annual grasses are more severe in lower elevation and drier plant communities. In other words, mid to low elevation sagebrush, most salt desert shrub, and Mohave Desert plant communities have shown themselves susceptible to ecological damage by annual grasses. We don’t really know how long, or what it would take, for a cheatgrass dominated salt desert shrub community to return to a more or less native plant community on its own. There are persuasive arguments that it won’t.

Many of Nevada’s noxious and invasive weeds came from regions with comparable climates in eastern Europe and western and central Asia. They were introduced through human activity, both accidentally and intentionally. Cheatgrass is believed to have come to the west as a wheat seed contaminant. Salt cedar was planted along streams for erosion control. Purple loosestrife was planted in gardens for its pretty purple flowers. In the intervening 100 years they have become noxious and invasive weeds.

Noxious and invasive weeds have a combination of traits that make them more competitive than natives. Tall whitetop, for example, produces thousands of seeds each year. Some of which can survive in the soil seed bank for 5 to 10 years. Plus it is rhizomatous. Rhizomes are underground stems with buds that can form new plants. Its roots can reach 20 feet deep in the soil. This combination of traits means that successful tall whitetop control requires years of treatment followed by decades of vigilance.

Cheatgrass also produces a lot of seed. It is a winter annual. The seeds germinate in the fall, put up some leaves, and then as soon as spring comes they grow to maturity and produce seed. Few native species have analogous life histories. Cheatgrass can initiate active growth at cooler soil temperatures than most natives. This means that the early spring growth of cheatgrass occurs largely free of competition from other plants. Cheatgrass spring growth is completed before active growth begins for most native species. During droughts cheatgrass can use up all the available soil moisture before the natives begin growing. Cheatgrass is more responsive to fire than most natives. Cheatgrass production is stimulated by nutrient release following fires. The native plants in the Great Basin that are released by fire are also adapted to the nutrient poor Great Basin environment. They do not respond as quickly or vigorously to fire as cheatgrass. This combination of traits means that in drier years cheatgrass can grow, use all the available soil moisture, and set seed, while the native plants may not even break dormancy. Both prolonged drought and fire favors cheatgrass over many native plant species.

Noxious weeds impact native ecosystems by:
• Reducing biodiversity
• Altering hydrologic conditions
• Altering soil characteristics
• Altering fire intensity and frequency
• Modifying successional pathways
• Competing for pollinators
• Displacing rare plant species
• Serving as reservoirs of plant pathogens
• Replacing complex communities with simple communities

Noxious weeds have economic impacts. In general, noxious and invasive weeds are expensive to control and can reduce agricultural production, property values, and water availability. It is estimated that invasive plants cause about $123 billion in damages and losses to the U.S. economy annually. About $5 billion are spent annually by agriculture to control weeds. A 1988 survey in Washington State found that 130 million pounds of forage were lost annually on knapweed infested rangelands. This equaled $951,000 in lost forage requiring the purchase $2.9 million of replacement hay. Total annual agricultural loses in North Dakota from leafy spurge are $87.3 million. Noxious weeds affect all Americans as an added cost of food production. A ranch in North Dakota that was badly infested with leafy spurge went on the market in 1975. It sold in 1991 for about $40 per acre. Comparable ranches without leafy spurge were selling for $100 to $125 per acre. In Klamath County, Oregon a 1,360-acre farm infested with leafy spurge sold for $27,000. Comparable farms without leafy spurge sold for $170,000 to $204,000. In Douglas County, Nevada the cost of treating 75 acres of tall whitetop was $12,647 in the year it was detected. Ten years later treatment costs had risen to $174,350.

While the preceding sounds bleak, oddly there is a positive part to the noxious and invasive weed story. Cooperative management of noxious and invasive weeds has clearly been a BLM success story for several decades. People who had nothing to do with each other now work together in cooperative weed management groups. Local service organizations, ranchers, and school kids get together to pull weeds. Much of the actual weed treatment that occurs on the public lands is done by cooperators and county weed crews.

Cooperative Weed Management Areas (CWMAs) are one of the ways this happens. CWMAs start for many different reasons, but successful CWMAs tend to have some common traits. First they have a geographic identity. To start this is often a group of landowners or a group of county and federal employees who decide to work together to tackle noxious weeds in a specific area, or a particular weed. BLM encourages and participates in many of these groups. Often BLM provides herbicide, a big upfront expense. As these groups gain experience they often get more neighbors involved, growing in size. Some of them move towards integrated pest management, including insects and controlled livestock grazing. As they mature and have success stories to show, some CWMAs start sponsoring field days, community events, and training sessions. While weed control from community weed pulling events may take years to show an effect, the public relation and educational values begin accruing at once. Where there are successful CWMAs the BLM weed specialists often spend much of the winter and spring working with the CWMAs to develop work plans, coordinate the next year’s activities, figuring out who’s paying for what, planning tours, spraying weeds, and reinforcing each others enthusiasm for weed control. There are laws that authorize the use of federal money on non-federal lands as part of coordinated noxious weed management.

In Nevada BLM weed specialists are actively engaged in 25 different cooperative weed management groups. All the BLM districts have cooperative weed management groups. The groups are composed of land owners; employees of County, State and Federal agencies; and members of the public. BLM also contracts several Weed Districts and Conservation Districts for weed control.

The two most common forms of noxious and invasive weed treatments on BLM lands are reseeding as part of ES/R and herbicides. BLM weed specialists receive training and hold federal and state licenses for the use of herbicides. Some herbicides are “restricted use herbicides,” which means a state license is needed to buy them. These are not the herbicides available at Lowes. Tordon and Escort, two herbicides widely used on BLM lands are restricted use herbicides. Tordon is commonly used on the knapweeds. Escort is used on whitetops and leafy spurge. People using such herbicides on public lands must hold state certification and be under the supervision of someone with federal certification.

BLM funding for noxious weed control steadily increased until 2001. Since then BLM Nevada’s funding for noxious weed management has been about $1.5 million, annually. A much more nebulous number is the amount of money spent on cheatgrass control. To date BLM Nevada’s biggest cheatgrass management effort has been post-fire emergency stabilization and rehabilitation (ES/R). The goal of ES/R is the reestablishment of perennial vegetation. This in turn prevents cheatgrass establishment or competes with the cheatgrass. Because the cheatgrass management effects are indirect and the results are variable, quantification of the cost of cheatgrass management is very difficult to determine.

Another cheatgrass management tool that recently became available for general use on BLM lands are herbicides containing the active ingredient Imazapic. These herbicides have been shown effective against annual grasses, including cheatgrass and medusahead. Plus, they can be somewhat selective. This means that a plant community that contains cheatgrass plus desirable perennial plants can be sprayed to kill the cheatgrass while having little or no impact on the desirable perennial plants. Imazapic can also be used in fire rehabilitation to reduce cheatgrass competition with the desired seeded plants. The use of herbicides always involves tradeoffs.


• Awareness – Learn to identify the noxious weeds. Be aware of your surroundings. Contact your local BLM weed specialist or University of Nevada Cooperative Extension Service with noxious weed identification and management questions. Extension has a wealth of noxious weed identification and management information ( look under “Natural Resources”). The Nevada Dept. of Agriculture (NDOA) offers herbicide certification training ( Join a CWMA near your home, or start one. NDOA can help do that.

• Prevention – Prevention is the cheapest and most effective noxious and invasive weed treatment. Simply don’t let them get started. Do not plant weed seeds or spread plant parts that can grow into new plants. That’s all there is to it.

Here are some ways to prevent the spread of weeds:
o Be cautious of new varieties of flowers that will “grow everywhere.” Purple loosestrife and Dalmatian toadflax were imported into the U.S. as garden flowers.
o Wash vehicles including the undercarriage and wheels. This should be the standard practice for individuals and agencies. OHVs easily transport viable parts and seeds of knapweeds and whitetops. The dried mud on field, ranch, construction, and fire vehicles can be weed seed banks.
o Drive on established roads and trails. These are the places people are looking for and treating noxious weeds.
o When using pack animals, carry only feed that is processed or certified weed free.
For 96 hours before entering public lands, feed pack animals only certified weed free feed.
Remove weed seeds from pack animals by brushing them thoroughly and cleaning their hooves.
o Sheep camps should be switched to weed free hay and processed feeds.

• Detection – If you find some noxious or invasive weeds, identify the location and extent of the infestation. Tell the landowner or land managing agency so they can take steps to control the weeds. The public is encouraged to report noxious weed infestations found on public lands to the Noxious Weed Specialist at the nearest BLM Office. Such reports need to include a very definite location. This could be a location on a detailed map, an unambiguous location description, or GPS coordinates (lat-longs or UTMs).

• Treatment – In order to effectively treat or manage noxious weeds you have to correctly identify and know something about them. For example, hand pulling established leafy spurge, tall whitetop, or whitetop may be worse than doing nothing. These are perennial rhizomatous species. Removing the above ground growth just activates buds on the rhizomes to produce new plants. It is unlikely that you will pull out all the roots. I know of a man in Reno who lives along the Steamboat Ditch. He has been pulling the tall whitetop in his back yard more or less weekly for over a decade. He’s down to not that much. He has about 90 feet of ditch frontage.

Conversely, a small patch of spotted knapweed, cheatgrass, or yellow starthistle may be controlled by pulling for several years until the seed bank is exhausted. Pulling works better for these species, because they are annuals or biennials, dependent on seed for the next generation. Once begun you will need to return to the location for several year before seed set and pull all the weeds you can find. This prevents resupply of the seed bank. Although most seeds can last for 3 to 5 years a few will last longer. After several years that infestation will be eliminated. The safest thing to do with the pulled weeds is put them in a plastic bag in the trash. Don’t use them for mulch. Composting may not kill all the seeds. Think about wearing gloves. Yellow starthistle has nasty spines. Spotted knapweed stems can be course and abrade your hands.

For further information or questions concerning BLM’s weed program in Nevada, please contact the State Weed Program Coordinator, Mark Coca at (775) 861-6475, or e-mail

Stop the Invasion! Prevent the introduction and spread of invasive species! Clean your vehicles, machinery, and boats.