2006-2007 Weed Management Handbook

Western Rangeland Weeds Resource

A Plant by Any Other Name  -  Another new web page provides access to a specialized segment of the GRIN database devoted to information on noxious weeds. Both taxonomy web pages are part of the GRIN database, which includes over 62,000 botanical names of mainly economic plants.

Montana Knapweeds: Identification, Biology, and Management

Leafy Spurge: Biology, Ecology and Management

Whitetop (Hoary Cress)

Leafy spurge will soon make its annual, albeit unwelcome,appearance on everything from range land to roadsides and railroad
right-of-ways.

Bob Richard, director of the USDA-Animal and Plant Health Inspection Service's Plant Protection Quarantine and Biological Control of Weeds Laboratory in Bozeman, says a lot of the success depends on how, where and when initial releases of biological control agents are made.

"We now know a lot more about how to make the initial release, which agents work best in which situations, and how many insects should be released," Richard said. "By taking a few of these things into consideration, you can significantly boost your chances of making a successful release and getting a good population of biocontrol agents established."

Richard, an entomologist, has made more than 2,000 releases of the host specific Aphthona species leafy spurge flea beetle in a variety of habitats spread across 19 states during the past 12 years. More than 80 percent of those releases have resulted in established populations that are now contributing to leafy spurge control.

"Establishment is absolutely the key," Richard said. "If you don't get good establishment, you can't expect good control."

Don Kirby, a professor of Animal and Range Science at North Dakota State University  said people also need to understand that biological control is a sustainable, long-term solution but not a "quick fix."

"Some people just aren't patient enough, and that's easy to understand - if you've got a leafy spurge problem, you want to get it taken care of NOW," Kirby said. "But biological control isn't going to work overnight - it's something you start with now to achieve inexpensive, permanent control in the future."

Some of the flea beetle release sites Kirby is studying are eight years old, but he said the results have been worth the wait.

"It's pretty impressive," he said. "We've seen dramatic reductions in leafy spurge stem densities - in some cases from 218 plants per square meter to five - and a corresponding increase in the production of desirable grasses."

The sites also provide a good example of why it's important to consider the long-term benefits biological control can provide, he added.

"Leafy spurge will never again be a deterrent to livestock production on these sites because the flea beetles will always be there," he said. "The flea beetles and spurge have reached a natural balance - if the spurge increases, flea beetle populations will increase and keep it under control.

The bottom line is simple: The sooner you get started, the sooner biological control will work."

Richard and Kirby offered the following generalities for increasing the chances of making a successful release of flea beetles:
 

•  Site location: Drier and sunnier is better, and some slope (to provide drainage) is a plus. "Flea beetles will move into shady, moist locations after a population is established, but we've learned that these are not good places to make an initial release," Richard said. There is also some variation according to species, he added. "Aphthona nigriscutis prefers a dry, sunny site while Aphthona lacertosa will tolerate a much broader range of locations."
• Timing: Insects must be released before they lay eggs! "If you release insects too late in the season, they won't reproduce and there won't be any insects next year," Kirby said. Although timing depends on several factors, including geography, elevation and climatic conditions, anything later than mid-July is considered too late, Richard said.
• Number of insects released: More is better. "Early releases generally consisted of 500 or fewer flea beetles, but we're now focusing on releases of at least 1,000," Richard said. "Releasing more insects enhances the chances of establishing a population."

Another common problem, Richard said, is that people often release insects at a site with lots of spurge but none of the other ingredients needed for a successful release.

"Again, people need to understand that successfully establishing a population is the key," he said. "If you can get a population started, they'll eventually move to the places where you most want or need control. But that may not be the best place to try and get a population started."

Richard admits he gets a little defensive when people say the insects failed to work.

"Failure is generally a result of how or where the insects were released," he said. "But we can now minimize establishment failure by using all of the things we've learned over the past 10 years. If you give leafy spurge flea beetles a decent chance, they'll work great!"

While ecologically based tools such as biological control are just one tool to controlling leafy spurge, Prosser pointed out.

"We want people to give biological control a chance, but we don't want them to ignore the other control tools that are available," he said.

"Herbicides are still the preferred tool for containing and preventing the spread of spurge infestations, for example, and sheep are an excellent mechanism for controlling spurge while diversifying cattle grazing operations. Biological control is just one of the tools that are available and can be used."

Prosser, Richard and Kirby encouraged people with questions about biological control to seek out the information that can help contribute to establishing a successful biocontrol site.

"If you have questions about biological control or Integrated Pest Management strategies for leafy spurge, give Dave Phillips, MSU Fergust County Extension Agent, a call at 538-3919 or email at acxdp@montana.edu.

Licking Houndstongue

Nina Zidack, an MSU plant pathologist, has been testing a common type of Pseudomonas bacteria to see whether it can control houndstongue. 

Tests suggest that this strain of Pseudomonas is one of the rare biological control agents that may work better in the field than in the laboratory. 

"It's success is aided by plant competition in the field," says Zidack.

The Pseudomonas is sprayed about June. It attacks new plant growth, interfering with its production of chlorophyll and making it turn white. There may be some regrowth a few weeks after spraying, but generally the plant has been sickened enough that it does not sprout the following spring.

"We're getting up to 80 percent control of the weed in the field," she adds.

Zidack says that some people might see a young houndstongue plant and think it was pretty. Those people haven't seen how houndstongue toxins kill livestock.

Houndstongue is primarily a problem in the northwestern United States. It is common along streams and creeks, where few herbicides are safe to apply. When it matures in its two-year cycle, it sends its seeds far and wide in the form of burrs that stick to everything that walks, from beaver to pant-legs.

Zidack began working with the Pseudomonas pathogen in 1996. Since then, she has worked both to increase its strength and to determine how best to apply it.

"It's native to this area, though the strain we have selected kills houndstongue four times better than the original type," says Zidack. 

She says the bacteria works best when applied with a surfactant--an additive that helps the bacteria enter the leaves of the weed.

Zidack has field trials in Gallatin, Park, Stillwater and Treasure counties. Like all biological control agents, this Because the Pseudomonas bacteria is spot-sprayed on houndstongue, non-targeted plants are not affected. At least one company is talking with MSU about its ability to make more useful plant pathogens to market as biocontrol agents to ranchers. Other MSU researchers working in the area include Dave Sands and Alice Pilgeram.

Ox-eye daisy is an alien weed invading disturbed areas of western and south-central Montana.  Many weed managers are concerned that ox-eye daisy has expanded rapidly over the past few years.  It is an introduced perennial from Eurasia.  The plant spreads by seeds and slowly extending shallow rhizomes.  Ox-eye daisy grows 10 to 24 inches tall with one to several stems arising from the same root. The upper leaves are smaller than the lower leaves.  The heads have the white ray flowers and yellow disk flowers typical of daisies.  Flower heads are borne singly on the ends of long stalks.

Some animals, including horses, cattle, sheep and goats will eat the weed.  In Montana, intensive grazing by cattle reduced ox-eye daisy by about 65 percent over the ungrazed treatments.  However, associated grasses were equally reduced and ox-eye daisy quickly reproduced from vegetative roots after grazing.  It bitter nature can impart a disagreeable flavor to milk of grazing animals.

Ox-eye daisy is resistant to normal 2,4-D applications.  At study conducted at Montana State University indicated that picloram (Tordon 22K) at a rate of 1 pint active ingredient per acre plus one quart of 2,4-D applied during the bud stage provided 100% control for over two years.  In the same study, Transline at a rate of 1.3 pints active ingredient per acre or Ally at a rate of 1/4 ounce active ingredient per acre plus a good surfactant provided similar control.  Studies in which herbicides were used in conjunction with fertilizer to stimulate grass growth showed an increase in forage production while ox-eye daisy populations were decreased.

Foothill and mountain pastures in the central Montana area are most likely to have populations of ox-eye daisy.  Keep a close watch on your pastures for this weed!

Common tansy (Tancetum vulgare), also known as golden buttons and garden tansy, is a perennial herb in the sunflower family.  The plant readily invades roadsides, fence rows, pastures, stream banks, and waste areas throughout North America.  While it is not a statewide noxious weed, it has been declared noxious in Broadwater, Beaverhead, Gallatin, Silverbow, Meagher, and Carbon counties.

Mature common tansy plants are easily recognized by the flat-topped clusters of small, button-like, yellow flowers they bear in the summer. Stems grow in large clusters up to 6 feet high and are mostly hairless, often purplish-red in color, and extensively branched towards the top. Leaves are finely divided into leaflets giving the plant a fern-like appearance.  Common tansy has a strong odor when crushed. Common tansy, native to Europe, has a long history of medicinal use.  It was first introduced to North America for use in folk remedies and as an ornamental plants. Use of common tansy led the governor of Massachusetts to list common tansy as a necessary plant for colonial herb gardens in the 1600s.  This led to widespread cultivation of the plant and its inevitable escape into fields and roadsides.  By the 1800s this weed was growing wild throughout the Northeast.  In 1912, it was reported as far west as Kansas and it was widespread in California by 1952. Limited research on control of common tansy has been conducted.  As with most weeds, prevention of the establishment and spread of infestations is
the most cost-effective management tool.  The most effective herbicide for common tansy control is metsulfuron (Escort).  In herbicide trials in northern Idaho, metsulfuron applied at 0.3 oz/acre yielded 99% control after three months and 98% control 15 months after treatment.  Metsulfuron should always be used with a high quality, nonionic surfactant to ensure penetration of the herbicide into plant tissues. Picloram (Tordon) also provides good, short term control of common tansy.

Neither of these herbicides should be used to control common tansy infestations near water as these chemicals are persistent in soil, and have potential to leach into groundwater.  Accordingly, metsulfuron and picloram should not be used on any site where the depth to water table is less than 20 feet.  This limits the usefulness of these chemicals for control of common tansy because the plants often grow near waterways.  Glyphosate (Rodeo) and 2,4-D amine are alternative herbicides for use near water, but
they are not very effective for controlling common tansy.  Mowing provides an alternative to herbicide use near waterways, and has been reported to marginally control common tansy.

Common tansy contains alkaloids that are toxic to both humans and livestock if consumed in large quantities.  Cases of livestock poisoning are rare, though, as tansy is unpalatable to grazing animals.

Noxious Weed Alert: New Yellow Starthistle Reports

 During September, the noxious weed yellow starthistle was found in Treasure County, which is thought to be the result of contaminated alfalfa seed. An additional report of the weed in Powder River County has

yet to be confirmed. 

"It's very aggressive," says Kim Goodwin, Montana State University-Bozeman weeds project specialist. "We've been trying to keep it out, but it keeps popping up in different areas of Montana." Goodwin and MSU Extension Noxious Weed Specialist Roger Sheley say that eliminating yellow starthistle should be an immediate priority whenever it is found, which is in disturbed areas such as rangelands, pastures, roadsides, cropland and wastelands. However, it can invade undisturbed plant communities as well.

"Once it becomes established it is very difficult to control," says Sheley. The weed produces as few as 700 seeds a year or as many as 170,000 seeds a year. It can cause a neurological problem in horses called "chewing disease." It also forms dense infestations, dramatically reducing rangeland diversity and forage production for livestock and wildlife. 

In the last few years, individual plants of yellow starthistle have been found in Carbon, Flathead, Gallatin, Lake, Ravalli and Sweet Grass counties.

Yellow starthistle is a winter annual forb with yellow flower heads. Each flower is located singly at the ends of branches. Sharp, straw-colored thorns that are almost an inch long distinguish flower heads.

Mature plants are two- to three-feet tall and have rigid, branching, winged stems that are covered with cottony hairs. 

Seedlings usually emerge in the fall, form rosettes and begin growing a taproot. Root growth continues throughout the winter. Yellow starthistle bolts in late spring and flowers June through August.

How to Control Yellow Starthisle

Yellow starthistle does not tolerate shade. Montana State University-Bozeman Extension specialists say it requires light on the soil surface for its usual winter development. It is capable of establishing on deep, well-drained soils as well as on shallow, rocky soils that receive from 10 40 inches of annual precipitation. It favors disturbed sites such as roadsides, ditches, orchards, and overgrazed rangeland and pasture.

Yellow starthistle should be immediately reported and then eliminated. Herbicides are the recommended method and are most effective when applied from the seedling to the early bud stages of the weed.

Picloram at 0.25 lb, dicamba, or 2,4-D at 1 lb active ingredient per acre are the most commonly used herbicides. Hand pulling can be used to remove small patches of yellow starthistle if follow-up management ensures that any overlooked plants are removed before to seed production. 

If plants are allowed to produce seed, the resulting seed bank in the soil combined with a long seed life make this plant extremely difficult to control. Prevent establishment by using only starthistle-free seed mixes and forage. Frequently monitor to implement early detection and eradication strategies. Encourage desired vegetation growth to provide resource competition, focusing on promoting healthy native plant communities.

Contact your local county agent or weed district supervisor for more information or to report a yellow starthistle sighting.

Starthistle closeup: 

Sharp spines are found on flower heads A 300 dpi version is on the web at:

http://www.montana.edu/wwwpb/ag/yellowstarthistle8.jpg

A quick-loading preview version is on the web at:

http://www.montana.edu/wwwpb/ag/yellowstarthistle8sm.jpg

Managing Weeds After Wildfire
By Kim Goodwin and Roger Sheley
MSU Land Resources and Environmental Sciences

The ecological effects of wildfires are often beneficial given the natural role of fire in perpetuating ecosystems. Depending upon fire intensity and plant characteristics, many plants will survive and reinitiate growth soon after a fire. The ability of plants to reestablish, thrive and reseed in subsequent years can be hurt if noxious weeds are inadequately managed.

Burned areas can contain high nutrient levels, exposed ground surfaces and reduced shade. These favor weed colonization and exponential weed growth, which can prevent reestablishment of desired vegetation and displace already established native plants. If permitted to reach large infestation levels, the resulting weed population will be very difficult and expensive to manage.

A well formulated and implemented burned area weed management plan can prevent weed establishment in both burned and adjacent unburned areas and help establish and maintain healthy, weed-resistant plant communities.

Burned areas may have inadequate competitive vegetation cover (below 30 percent). In such cases, it will be necessary to provide a desired plant community that can suppress weeds through resource competition.

Revegetation, when necessary, can be a first step in the implementation of a burned area weed management plan.

A seed mix should contain a diversity of aggressive, quick-establishing grasses and forbs, though forbs should not be included if broadcast treatments of broadleaf herbicides are anticipated. This mix should be able to effectively occupy available burned area niches. Such a plant community is likely to be weed-resistant, because few soil resources are available to a potential invader.

The most successful burned area revegetation efforts have been observed with a fall-dormant broadcast seeding directly into the ash layer immediately after the fire. Burned area revegetation conducted the year after a fire will benefit from seed placement with a no-till drill if the ash layer is absent. If the site is inaccessible to such equipment, doubling or tripling the broadcast seeding rate based upon drill seeding or plowed ground will enhance establishment success.

Integrated weed management is an ecological approach to prevent and manage weed populations. A burned area IWM plan includes: prevention and monitoring strategies, effective in precluding spread and establishment into weed-free areas; eradication of small populations; a cumulative approach in large infestation management towards reestablishment of healthy plant communities.

Preventing weeds from spreading through seed dispersal is the most effective and least costly method of weed management. Because of this, use only certified noxious weed-free seed mixes, forage and mulch; thoroughly clean vehicles and equipment before entering weed-free burned areas; and eradicate or contain adjacent weed populations.

Surveying burned areas to eradicate new weeds through an organized monitoring plan is essential to prevent weed establishment. Monitoring should occur at least three times (spring, summer, fall) and concentrate where weed infestations often begin: along fire lines, roadways, railways and waterways.

Newly established populations or those smaller than 100 square feet are most responsive to eradication. Individual weeds must be removed and steadily replaced with desired vegetation until all viable seeds are depleted from the soil. Seed dormancy and longevity mean that long-term management is required for eradication. If eradication is to succeed, reproduction must be stopped completely.

No method or integration of methods can achieve eradication for large weed populations. Management towards reestablishing healthy plant communities is the most practical management option. This involves shifting the competitive balance from the infestation to the desired plants by revegetating, if necessary, after the infestation has been weakened through an integration of mechanical, chemical, cultural and/or biological controls.