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Chemical, Mechanical and Cultural Control

Herbicide

Tansy ragwort can be controlled using auxinic herbicides (mimics of auxin, a naturally-occurring plant growth regulator). The best timing of application is when tansy ragwort is actively growing in the rosette stage either in the spring or mid-fall. Herbicides are less effective after

plants have bolted to produce flowers. In most cases reapplication of herbicide or integration with other control methods will be needed for sustained population reductions. The amine, low-volatile ester, or emulsifiable acid formulations of 2,4-D are effective when applied at 2 lb. a.e./ac. (two pounds acid equivalent per acre). Always check the herbicide label to confirm formulation and proper usage of the product before applying. When using 4 lb. a.e./gal. (four pound acid equivalent per gallon) formulation, apply the mixed product at a rate of 2 qt./ac. (two quarts per acre).

Tansy ragwort is listed on the following herbicide labels at rates in parentheses: picloram (1-2 qt./ac.), aminopyralid (5-7 oz./ac.), metsulfuron (0.5-1 oz./ac. with nonionic surfactant at 0.5 percent [%]), and chlorsulfuron (1-3 oz./ac. with nonionic surfactant at 0.5% volume to volume). Metsulfuron and chlorsulfuron should not be applied where soil pH is greater than 7.9 because under these conditions chemical breakdown is slow resulting in extended residual activity that increases the risk of off-site movement of the chemical and non-target plant injury. Consult individual herbicide labels for other possible soil pH restrictions.

Herbicides are most effective where competitive desired plants are present to fill voids in the plant community following successful tansy ragwort control. However, herbicide injury to non-target desirable broadleaved plants and some grasses should be expected; consult product labels for further information on potential non-target injury. To avoid non-target injury, apply herbicides in the fall after desired plants are dormant for the winter. This tactic is most effective when using herbicides with low residual activity. Always follow label instructions to reduce toxicity or other unintended risks to humans and the environment, and to confirm potential grazing and replanting restrictions. Consult your local County Extension agent or weed coordinator for herbicide recommendations in your area. Herbicide treatments typically increase the concentration of water-soluble carbohydrate in tansy ragwort, making it more palatable to livestock and thereby increasing the risk of alkaloid poisoning. Grazing should therefore be deferred for 3-4 weeks after herbicide application.

Note: Any mention of specific products in this publication does not constitute a recommendation by the NRCS. It is a violation of Federal law to use herbicides in a manner inconsistent with their labeling.

Hand Pulling

Hand pulling and digging that extracts all of the caudex and fleshy rootstock is an effective method to temporally reduce tansy ragwort on small-scale infestations and scattered plants either as new invaders or those persisting after herbicide treatments. Pulling rosette and flowering plants will reduce seed set. Follow-up management will be needed to eliminate plants regenerating from root fragments or seed. Protective gloves are recommended to be worn as a precautionary measure by anyone handling tansy ragwort.

Mowing

Mowing is not an effective control for tansy ragwort. Rosettes are flat to the ground and may be missed by the mower blade, and when clipped, vegetative reproduction is stimulated. Mowing when plants bolt to flower may temporarily reduce seed production; however, plants will survive to flower again. A dispersal study found achenes dispersed as much as two and a half times farther on mowed sites than where the natural vegetation remained. However, in Switzerland, frequent mowing promoted fast-growing grass species and was associated with reduced occurrence of tansy ragwort. Mowing to maintain vigorous grassland communities may help prevent tansy ragwort invasion.

Tilling

The roots and caudex of tansy ragwort have the ability to regenerate after they are broken-up by tilling. Therefore, tillage has the potential to spread tansy ragwort and is not recommended by itself. The disturbance of tillage can create a favorable environment for tansy ragwort growth and reproduction by reducing competitive perennial plants. Tillage should be combined with herbicide management and followed by revegetation with desired, competitive plants.

Irrigation

Tansy ragwort thrives under mesic conditions and therefore irrigation is not recommended as a control by itself. Where tansy ragwort invades irrigated pastures and hayland, carefully planned irrigation management will stimulate the competitiveness of the forage crop and when combined with nutrient, forage harvest, and grazing management practices will help prevent the re-establishment of tansy ragwort after other control practices are applied.

Fertilization

Tansy ragwort is found on pastures of low to moderate nutrient status in Switzerland, which is part of its native range. A Swiss study found the amount of plant-available nitrogen was one of the most important factors predicting the occurrence of tansy ragwort. The model developed from that study predicted a fivefold reduction in the risk of tansy ragwort occurrence by doubling the application of nitrogen from about 50 lb./ac. to 100 lb./ac. On cultivated pastures and hay meadows, nutrient management is important to maintaining the competitiveness of desired perennial grasses. Nutrient management combined with judicious use of herbicides and crop rotation is recommended where tansy ragwort invades non-native pastures and hay meadows.

Prescribed Burning

Fire is reportedly effective in killing reproductive tansy ragwort plants and achenes. Fire is also used to maintain the vigor and density of grassland communities by burning excess plant litter and possibly increasing soil fertility. Fire can therefore be used as a preventative measure or in combination with other control methods to reduce tansy ragwort populations. On forested sites and clearings, the disturbance caused by fire may create openings favorable to tansy ragwort invasion.

Grazing Management

The way grazing is managed is an important factor influencing localized presence and distribution of tansy ragwort in its native range. In the Swiss study referred to in the Fertilization section above, continuously grazed pastures were 11 times more likely to be infested by tansy ragwort than pastures managed under rotational grazing because the former management regime resulted in more openings in the grass canopy where tansy ragwort could establish. Pastures that had greater than 25% uncovered soil had a 40-fold greater risk of tansy ragwort occurrence than pasture with less than 25% bare ground. Prescribed grazing that maintains a continuous grassland community is recommended both for the prevention of tansy ragwort invasion and in pastures where it is already being controlled.

Tansy ragwort leaves and flowers exceed the standard protein and digestibility requirements for sheep. In addition, sheep seem immune to the plant’s toxic alkaloids, and are willing grazers of young plants. In New Zealand, intensive sheep grazing is the predominant management approach for tansy ragwort; the weed generally does not occur where sheep are regularly stocked. In an Oregon grazing study, tansy ragwort seed production was prevented and plant mortality was attributed to sheep grazing in the summer following cattle had grazing in the spring. A separate study found tansy ragwort plants subjected to 75% defoliation were able to compensate fully five months after treatment when grown without competition. When grown in competition with Richardson’s fescue (Festuca rubra), there was no re-growth after 75% defoliation. These studies suggest sheep grazing is effective in controlling tansy ragwort where it grows in a competitive grassland community.

Revegetation

The information presented above strongly suggests tansy ragwort is not competitive in a closed plant community. Control of tansy ragwort regardless of method will most likely be short term where competitive plants are absent. In western Montana, tansy ragwort commonly invades in forest communities after logging because the disturbance associated with logging creates favorable establishment sites and the logging equipment often serves as a vector of spread. Seeding rapidly establishing perennial plants after logging is therefore extremely important to preventing or reducing the severity of tansy ragwort infestations. In forage crop fields, crop rotation can facilitate tansy ragwort control while keeping the crops vigorous and competitive.

Plant species selected for revegetating disturbed sites likely or known to be infested by tansy ragwort should be appropriate for management objectives, adapted to site conditions, and competitive with the weed. Management objectives will determine if forage species or native species should be seeded and specific species mixture components. The environmental conditions of the site, including precipitation, soil texture and depth, slope and aspect, will affect species establishment. On native rangeland, a diversity of perennial grass and forb species that occupy many niches over time and space will most fully utilize available resources and compete effectively with tansy ragwort. Refer to Montana Plant Materials Technical Note 46, 'Seeding Rates and Recommended Cultivars,' and Extension Bulletin EB19 'Dryland Pasture Species for Montana and Wyoming' for seeding rate guidance and revegetation species selection. State, area, and field resource specialists can help determine the most appropriate, site-specific species mix and timing of seeding for local conditions.

Integrated Pest Management (IPM)

Tansy ragwort thrives on disturbed ground with open sites in the plant community. On hay ground, IPM practices include crop rotation, nutrient management, irrigation management (where available), and forage harvest management to maintain a competitive closed plant community. New infestations of tansy ragwort should be aggressively controlled using hand pulling and/or broadleaf herbicide. On pastures and rangeland, herbicide application should be combined with prescribed grazing. Multi-species grazing with cattle and sheep will provide more uniform utilization than single-species grazing. In the spring, grazing sheep first to target tansy ragwort before grazing with cattle will prevent accidental poisoning of cattle. When tansy ragwort plants are mature, cattle will avoid them. Severe infestations should only be grazed by sheep. Forest clearings should be revegetated and monitored for new infestation after logging operations. Roadways, trails, and irrigation ditches should be maintained weed free.

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Last Modified: 06/22/2009