The of bitterweed (Hymenoxys odorata) — yellow flowers sprouting in the pastures and rangeland of the Southwest — may cause farmers and ranchers to groan. This yellow-flowered plant, a member of the aster family (Asteraceae), is poisonous when eaten by sheep, cows and other livestock.
Bitterweed, also known as western bitterweed or rubberweed (Hymenoxys odorata), is a bothersome weed that can take over pastures and lawns in the southwestern United States. This invasive plant produces thousands of seeds per plant and spreads aggressively, crowding out desirable grasses and forbs. Left uncontrolled, bitterweed can become the dominant vegetation, leading to bare ground and soil erosion.
While bitterweed is not harmful to touch, it can be toxic to livestock and wildlife when ingested. Sheep are especially susceptible, with as little as 0.5% of their body weight in green bitterweed plants enough to be lethal. Cattle, goats, and horses can also be poisoned. Bitterweed poisoning leads to symptoms like appetite loss, abdominal pain, trembling, and difficulty breathing. Without treatment, death usually occurs within days.
So what can you do to get rid of this problematic weed? Here are some effective methods for bitterweed control and eradication in pastures and lawns
Promote Healthy Grass Growth
The best long-term approach for controlling bitterweed is to promote vigorous growth of desirable grasses and forbs that can outcompete the weed. Bitterweed thrives in overgrazed pastures where bare ground allows its seeds to germinate and establish. If you reduce stocking rates and use rotational grazing to avoid overgrazing, grasses will be healthier and make it harder for bitterweed to invade.
Other tips for improving grass growth:
- Test soil and apply needed fertilizer, lime, or soil amendments
- Overseed thin areas with desirable grass and legume species
- Aerate compacted soil to improve drainage and root growth
- Control other weedy species that may outcompete grass
With strong perennial grasses and legumes covering the ground, bitterweed will struggle to establish and spread.
Herbicide Application
Using selective herbicides is an effective way to kill existing bitterweed plants while leaving grasses unharmed. Recommended options include
- 2,4-D amine at 1-2 pts/acre applied in May or early June
- Dicamba + 2,4-D formulation
- Metsulfuron (eg. Cimarron Plus)
- Aminopyralid (eg. GrazonNext HL)
Always follow label directions for correct timing, rates, and grazing restrictions when using any herbicide. Avoid spraying near sensitive crops, gardens, or bodies of water. Combining herbicide use with improved grazing practices provides the best control.
Hand Pulling and Digging
For small infestations, manually pulling and digging bitterweed can eliminate plants and prevent seed production. Use a sturdy digging tool to uproot entire taproots to prevent regrowth Pull plants before they produce flowers and seeds to prevent spread.
Place pulled weeds in plastic bags and dispose of off-site, away from areas where seeds may re-establish. Wear gloves while pulling to avoid skin irritation from plant juices. Hand pulling is time consuming but useful for controlling patches and scattered plants.
Mowing and Cutting
Mowing bitterweed before it flowers can help limit seed production and spread. However, plants may still regrow from the stem base unless cut very low to the ground. Combining mowing with herbicide use is most effective. For spot treatment of patches, string trimmers or brush cutters can be used to cut bitterweed down.
Be sure to clean equipment thoroughly after use to avoid spreading seeds to new areas. Dispose of cut material off-site or burn if allowed in your region. Avoid mowing when seeds are present.
Prescribed Burning
Conducting prescribed burns can kill some bitterweed plants and seeds. However, bitterweed is adapted to fire and will likely resprout after low-intensity burns. Follow up burning with herbicide application on regrowth for best results. Only conduct burns where safe and legally allowed.
Grazing Management
While bitterweed can be toxic if eaten in large quantities, some livestock species like goats and cattle are more tolerant than sheep. Rotational grazing can utilize their preference for grass over bitterweed to help control infestations while minimizing risk. Avoid continuous grazing and overgrazing, which favors bitterweed.
Reseeding Treated Areas
Once bitterweed is removed, reestablishing desirable vegetation is key to prevent reinvasion. Consider reseeding treated areas with competitive grass and legume species adapted to the site. Use high seeding rates to quickly establish dense cover.
Prevention and Early Detection
Regularly scouting pastures and lawns can help detect bitterweed invasions early while populations are small. Controlling new patches before they spread prevents more extensive infestations. Avoid overgrazing and poor soil health to limit habitat suitability for bitterweed.
Cleaning equipment, vehicles, livestock, and shoes when moving between properties controls bitterweed seed spread. Pay close attention to supplement and hay sources as well, as bitterweed seed can unknowingly be brought in.
Integrated Bitterweed Management Plan
The most effective approach often combines multiple methods, such as:
- Improving soil health and grass/forb cover
- Selective fall herbicide application
- Spot treating patches by hand pulling, mowing, or digging
- Rotational livestock grazing
- Reseeding treated areas
- Careful prevention and early detection
With persistence using an integrated plan, bitterweed can be successfully removed from pastures and lawns and kept under control long-term. The key is not allowing it to grow and spread unchecked in the first place through good management practices. Talk to your local agricultural extension agent for help developing a customized bitterweed control strategy for your specific site and conditions.
When to Seek Professional Help
For severe, extensive infestations, contacting a professional pasture management service may be warranted. Companies can develop a prescription treatment plan and provide services like large-scale herbicide application, prescribed burning, and reseeding that may not be feasible to undertake individually.
Seeking professional help can speed up control of widespread bitterweed. Costs may be well worth it to avoid livestock losses and regain pasture productivity sooner.
Bitterweed is a challenging foe, but by understanding its growth habits and implementing a targeted, multifaceted management plan, you can get rid of this invasive weed from your pastures or lawn. With vigilance and persistence, your fields can once again be dominated by desirable, productive vegetation rather than the yellow flowers of bitterweed. Don’t let this toxic plant take over your property – take action today using proven integrated control methods.
What Is Bitterweed?
If bitterweed grows in your area, its important to recognize what it is before it affects your livestock. Getting rid of bitterweed before it becomes a problem is the easiest way to control it. Bitterweed is an annual with straight stems that grow up to 2 feet. The plant bears yellow flowers that surround a yellow seed head. Bitterweed multiples because winds pick up these seeds and spread them.
Bitterweed grows across a swath of the Southwest, mostly from southern Kansas south to Mexico and from central Texas to California. Livestock often try to graze on bitterweed in winter and early spring when other foliage is dormant. Bitterweed grows best in spring and early summer, but the plant may bear seedlings at any time of the year depending on rain and temperature. More Like This
Bitterweed has a close cousin, pingue (Hymenoxys richardsonii), a perennial that resembles bitterweed and has a similar toxic effect on livestock. Like bitterweed, livestock wont eat pingue if grass and other forage are available. Another type of bitterweed, Helenium amarum, grows in southeastern and south central states and is toxic to livestock when eaten in very large quantities.
Control Bitterweed in Pastures
If you have bitterweed growing in your pasture, you want to eliminate it because it is particularly toxic to sheep. Sheep are more likely than other livestock to eat bitterweed. Its name comes from the sour milk produced by animals that eat the plant.
Bitterweed not only makes milk taste sour but it also tastes bitter to most livestock. Unless there is no other forage available, livestock will typically not eat bitterweed. One way to control the growth of bitterweed without using pesticides is to mow it and to plant vigorous perennial grasses, which will then crowd out the bitterweed. Another way is to rotate livestock through various pastures.
You can control bitterweed with pesticides applied from fall to early spring but make sure livestock are not feeding in the pasture. Use 2,4-D, picloram, clopyralid or metsulfuron no later than early spring, before the plant starts to flower. Be sure to follow the directions on the label when applying the herbicide and heed any precautions, especially the time frame before re-introducing livestock to the pasture.
Bitterweed
FAQ
What will kill bitterweed?
Bitterweed is readily controlled with 2,4-D amine at 1 to 2 pt/A applied in May or early June.
What kills bitter sneezeweed?
Bitter Sneezeweed is toxic to livestock and should be managed appropriately. 2,4-D and Grazon provide good control in pastures and should be applied when the weed is less than two inches tall and actively growing. When applying a pesticide make sure you read the label and wear the PPE it requires you to wear.
How to get rid of bittercress naturally?
While pulling and spraying can clean up a current outbreak of hairy bittercress, that likely won’t stop new weeds from germinating in the fall to create a repeat problem next winter. In garden beds, a two-inch layer of mulch can help smother hairy-bittercress seeds and prevent them from germinating.
How to get rid of bitter dock plant naturally?
To control docks without the use of chemicals
Dig up individual plants by hand, aiming to remove as much of the tap root as possible, as only the top 15cm (6in) of root is able to re-grow into a new plant.