Table of Contents
Coltsfoot (Tussilago farfara) is a perennial weed native to Europe, North Africa and parts of Asia. It was introduced to Canada in the 1920's, and can now be found in most provinces. It has been positively identified through the Weed Alert Program in 27 counties in Southern Ontario. While widespread in Southern Ontario, coltsfoot is still found on only a relatively few farms. For example, up to 1986, it has been reported on only 10 farms in Middlesex County. The most common location for coltsfoot is on roadsides, both township roads and highways. From this foothold, it can spread by seed or rhizomes to adjacent fields. While this weed has not spread rapidly, it is of concern because there are very few herbicides that will control it adequately, and it thrives in several crops.
Figure 1. Coltsfoot patches in winter wheat, late flower
stage in early May.
Figure 2. Coltsfoot patch in flower, late April. Note absence
Figure 3. Coltsfoot, flowers and unopened seed heads.
Figure 4. Fully developed coltsfoot leaves in July.
Figure 5. Rhizomes and emerged flower heads.
Figure 6. Coltsfoot patch in corn in June. Leaves only partially developed.
Figure 7. Coltsfoot patches in seed on roadsides.
Coltsfoot is a low growing perennial plant. It has large, deep green leaves, somewhat similar in size and shape when fully grown to those of velvetleaf or cocklebur. The plant has no main stem, however. The leaf petiole holds the leaves 10 to 20 cm above the soil, often forming a complete canopy covering the soil. The top leaf surface has a smooth, almost waxy appearance, while the underside of the leaf is covered with white wool-like hairs. Usually leaf stems and larger leaf veins are distinctly purple in color.
Coltsfoot spreads by underground rhizomes, which develop mainly in the plow layer (5 to 20 cm deep). These rhizomes produce quite dense stands of above-ground foliage. It is common to find only 2 or 3 patches of coltsfoot in a field, with patches gradually expanding outward due to rhizome growth. These patches usually range from 3 to 6 metres in diameter. Coltsfoot has a very unique flowering characteristic. The bright yellow flowers, similar to dandelions but slightly smaller, appear early in the spring, before any leaves emerge. In Southern Ontario, coltsfoot flowers in April, often before the last of the snowbanks have melted. Flower heads have even been known to push through snow. The white, fluffy seed heads also resemble those of dandelions. However, coltsfoot seed will mature by the time the very first dandelions are coming into bloom. Coltsfoot is not a prolific seed producer compared to many annual weeds, with each plant reported to produce about 3500 seeds.
As seed on earlier flowers ripens, the coltsfoot leaves finally begin to emerge above ground. Leaves will continue to grow in number and size for several weeks, so that the canopy does not reach full density until late June to mid-July. During the summer, food is stored in the rhizomes for the following year's early spring growth.
Coltsfoot has the ability to thrive on gravelly soils, and is a common weed in gravel pits. When gravel from infested pits is used in roadbed maintenance, some rhizomes survive, and start up new coltsfoot patches. Coltsfoot seems to compete strongly with the roadside grasses, and is not controlled by commonly used roadside herbicides. Eventually the patch may expand to creep under the fence and into an adjoining cultivated field. Tillage operations can then spread the weed throughout the field. Seed blown by the wind may also start new patches, depending on the herbicide program being used on the field where the seed germinates.
In field crops, coltsfoot has been reported in corn, soybeans, winter wheat, spring grain and alfalfa stands. Once well established, coltsfoot appears to hold its own against competition from these crops. Field observations indicate that tillage equipment, particularly chisel plows and cultivators, will carry rhizomes from a main patch, and drop them elsewhere in the field, giving rise to new patches. The spread of coltsfoot by this method is much slower in a field than is the spread of quackgrass. However, if not controlled, coltsfoot can in time take over a field.
While no doubt seed is a method of reproduction, it is much less significant than for the common annual weeds. Seed production is relatively low, and seed of coltsfoot will completely lose its viability one year after production.
Field observations and research trials indicate no control of established coltsfoot by the herbicides 2,4-D, MCPA, 2-4DB, Kil-Mor®, Banvel® or Basagran®. Rates of atrazine up to 2 kg/ha active have not given control in corn. The ppi and pre herbicides registered in soybeans have not given control.
Roundup® has been used for the non-selective control of coltsfoot and has often given good control. Poor control has usually been due to herbicide application too early in the season. Coltsfoot foliage is slow to develop in the spring, particularly if the field has been worked and planted to a crop. Leaves may not be fully developed until late June or mid-July. Application of Roundup at an earlier stage will kill all foliage, but not eradicate the rhizomes.
When coltsfoot is detected while it is still present in only a few patches, the application of a 2% solution of Roundup in water, applied to runoff on fully developed coltsfoot leaves, has given good control. A knapsack sprayer works well for such an application. If applied in corn or soybeans, apply before corn starts to silk or soybeans begin to pod. The crop will be killed in the sprayed area.
Control in an alfalfa stand is often not practical. There may not be sufficient foliage development in coltsfoot prior to each alfalfa harvest. Since Roundup will also kill the crop in the sprayed area, the sprayed spots soon become infested with other weeds such as dandelions. Any affected forage in the treated spots cannot be harvested until treated plants turn brown.
To date, most coltsfoot occurs in only a few patches in a field. If the weed has been well distributed in a field by tillage operations, it may be necessary to apply an overall spray in a non-crop situation.
Additional information on use and precautions when using this herbicide is available in the Ontario Ministry of Agriculture, Food and Rural Affairs publication 75, Guide to Chemical Weed Control.
The best approach to coltsfoot control is to stop its spread when only a few patches are present and before it becomes a serious problem throughout the field or farm.
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