Canada thistle is just one of the many broadleaf weeds that may be lurking in your horse pasture.
Do you have broadleaf weeds in your horse pasture? Of course you do!
“Broadleaf” is a term used for a group of plants that have leaves that do not look like grass. When that plant is an invasive weed found in your pasture, it reduces the health of the land and competes with the forage you are hoping to provide your animals.
Common broadleaf weeds found in local pastures include tansy ragwort, oxeye daisy, false dandelion, and Canada thistle. There are identification guides for these and other common weeds online or you can use the iNaturalist app that you can download to your smartphone. This app can help you be more efficient when scouting your pastures. Identification can also help you save the broadleaf plants in your pasture that are good forage for grazers.
That Broadleaf Weed May be Toxic!
Just as important as selecting the best types of forage plants for your pasture is avoiding invasive plants that can be toxic or cause harm to your horses. Check out our Pasture Bullies publication for common plants that are toxic to horses.
Speaking of toxic plants, be on the lookout for plants that accumulate nitrates such as lambsquarter and redroot pigweed. Learn more about high nitrate and oxalate plants here. There are also plants coming up in spring pastures that contain alkaloids which are lethal to most livestock, including horses! Learn more about alkaloids here. These plants include comfrey, groundsel, fiddleneck, houndstongue, and the particularly notorious Tansy Ragwort.
Do not be fooled by the pretty Tansy ragwort flowers!
Tansy Ragwort is Pasture Public Enemy #1
Tansy ragwort leaves emerge as a rosette in the first year and then return in the second year to produce bright clusters of daisy-like flowers. The best plan is to control the plant in the first year instead of racing against time to control it before the flowers go to seed in the second year.
Control tansy ragwort by using biological, chemical, and/or manual methods. As with any control method, it is important to avoid disturbing the soil as much as possible. Soil disturbance can bring buried seeds to the surface, and lead to increased soil erosion. Due to the toxicity of tansy ragwort, be sure to wear gloves and protective clothing when removing this plant.
You may pull or dig out Tansy ragwort plants. The best time to pull plants is between May and June after they bolt (sudden growth of a flower stalk) and before they flower. Pulling and digging are easier when the soil is moist. Later in the season, soils dry and harden making tansy ragwort plants much more difficult to remove. If you are digging out rosettes, remove as much of the root as possible.
Tansy ragwort forms a rosette in the first year.
Take Control of Your Broadleaf Weeds
Late spring/summer mowing is a good control method for the control of many broadleaf weeds. However, mowing is not a suggested means of control for tansy ragwort. While mowing may prevent the plant from immediately producing seeds, it also stimulates additional growth. This leads to more plants and more stems per plant in the same season! To make matters worse, mowing in pastures can spread the toxic leaves making it harder for grazing animals to avoid.
Be sure to remove pulled or dug-up tansy plants from pastures and hayfields. Bag and dispose of these plants as garbage. For large infestations, remove plants from the field, pile and cover them in an area inaccessible to livestock. Be careful to prevent the dispersal of seeds, as seeds can develop even after pulling the plant.
Herbicide application can also be an effective means to control tansy ragwort infestations. But, beware! Both mowing and spraying will create wilted plants which actually become more palatable to livestock. Wilted or dried tansy retains the toxins and, whether consumed in the field or mixed in the hay, it is poisonous. It is always best to remove dead plants from pastures.
Tansy ragwort is susceptible to several systemic herbicides. Be cautious when using herbicides on pasture with grazing animals. You can find chemical recommendations for tansy in the Pacific Northwest Pest Management Handbook.
Be Aware of Beneficial Weeds in Your Pastures
An important thing to note — if you treat broadleaf weeds with herbicides, you are also going to reduce your beneficial broadleaf legumes like clover, vetch, and trefoils. You will also reduce edible weeds like plantain and chicory.
Make a point to know which plants are in your fields so you can make a good decision on whether to broadcast spray or spot spray. If your pasture contains mostly edible weeds and clover, do not use a broadcast spray that will also kill the beneficial plants. Consider spot spraying the weeds and leaving the other plants alone. However, if you have mostly non-edible or toxic weeds, you might consider broadcast spraying. Not certain? Check with your local Soil and Water Conservation District for assistance.
Oxeye Daisy is an invasive broadleaf weed that can be found in horse pastures. (Photo: USDA.gov)
Healthy Pastures Mean Less Weeds
In general, a healthy pasture is the best defense against invasive weeds. However, until you have a lush healthy pasture, here are the steps to consider for successful control of most pasture weeds:
- Identify weeds.
- Pull, mow, dig, or spray established weeds.
- Bring in other livestock to graze undesirable plants.
- Cut off and remove weeds before seed heads develop.
- If you choose to use an herbicide, select the right one and apply it at the right time in the weed’s growth cycle. Read the label and follow all directions.
- Analyze soil and use test results to correct nutrient deficiencies that may limit grasses’ ability to compete with weeds.
- Use the grazing practices outlined in this publication to encourage desirable pasture plants.
From Managing Small-Acreage Horse Farms in Western Oregon and Western Washington
By Melissa Fery, David Hannaway, Garry Stephenson, Linda J. Brewer, and Scott Duggan
Healthy pastures, fewer weeds, happy horses…hmmm. This sounds like a worthy goal!
If you need help with your pastures, check out the links in this article for additional information. You can also contact our office and talk to one of our conservation planners. Contact the Clackamas Soil and Water Conservation District at 503-210-6000 or email us at planners@conservationdistrict.org.