Grazing Control, Cultural Control and Biological Control

Grazing Control

Common tansy is reported to be toxic to livestock and abortions in cattle were reported from the mid-west United States. However, in Montana most classes of livestock and some wildlife have been observed to eat common tansy with no known adverse effects. The potentially toxic volatile oils produced by the leaves and inflorescences of common tansy can be metabolized by mammals and the metabolites excreted in the urine. Research indicates that herbivores have a toxin blood-level feedback mechanism for some of the oils produced by common tansy that, when threshold levels are reached, deters further grazing. This natural feedback mechanism may be sufficient to prevent poisoning as long as alternative forages are available to the herbivores.

Sheep have been used to manage common tansy in Montana. Clipping data from grazing enclosures paired with grazed plots suggest sheep consumed up to 90percent of the aboveground bio-mass of common tansy while consuming a slightly greater or lesser quantity of perennial grass bio-mass depending on the availability of each forage class (where more common tansy than grass was available, more common tansy relative to grass was consumed). Long-term impacts of repeated sheep grazing on common tansy population size and plant community dynamics are not known, but observations suggest common tansy populations may be decreased and grass populations increased with consecutive years of season-long sheep grazing (see Figures 5a and 5b). While no toxic effects of eating common tansy were reported from the flock used in the study, it is recommended to remove sheep from common tansy infestations four weeks prior to breeding to avoid reproductive problems. Similar grazing recommendations most likely apply to goats.

Photos of a common tansy population in western Montana grazed by sheep for two years;

Figure 5a.  a. the plant community in 25 June 2004 before sheep grazing started;

Figure 5b. the plant community in 15 May 2007 after three seasons of grazing.

The difference in season between photos does not provide an accurate comparison considering grasses may initiate growth in the spring before common tansy. However, it appears that grasses are increasing where sheep have grazed.

Cultural Control

Plant competition reduces the invasiveness of common tansy and increases the effectiveness of control applications. Therefore, practices that increase the competitiveness of desirable plant species such as conservation crop rotation, nutrient management, irrigation water management, forage harvest management, critical area planting, and prescribed grazing will make the environment less hospitable for common tansy to survive and spread.

Biological Control

Currently, no biological control agents are available for management of common tansy. There are numerous insects and diseases that attack common tansy in its native range and several biological control insects have been identified: Isophrictis striatella is a moth that mines the flowerhead, stem, and rhizome; Microplonus millefolii is a stem-mining weevil; moths in the Dichrorampha genus feed on rhizomes; Cassida stigmatica beetles feed on leaves; and the gall midge Rhopalomyia tanaceticola attacks the rosette, stem, and flowerhead. A joint United States and Canadian consortium is currently funding a program of insect biological control of common tansy.

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Last Modified: 02/27/2008