Cressleaf Groundsel Identification and Control

Cressleaf groundsel (Packera glabella, formerly Senecio glabellus) has spread in Ohio since the early 1900s. With the adoption of no-till or reduced tillage, cressleaf groundsel has become more prevalent in Ohio across a variety of cropping fields, pastures, and other landscapes. Also called butterweed, this plant can spread aggressively. It has poisonous characteristics, making it a potentially toxic weed for livestock.

Characteristics and How to Identify

Part of the Asteraceae family, cressleaf groundsel is considered a winter annual weed, meaning that it emerges in the fall, and flowers and sets seed the following spring. Once the plant reaches maturity, it reproduces hundreds of thousands through seed. Cressleaf groundsel thrives in every habitat under cool, wet conditions. It does not grow well in hot, dry conditions.

Fruits/Seeds Seeds are white with feathery structures (not dissimilar to dandelion seeds); they spread mainly by wind.
Leaves Seedlings form a basal rosette, with leaves in an alternate pattern. Leaves are deeply lobed with a slight round-toothed leaf edge.
Stems Hollow stems are a key identification characteristic for cressleaf groundsel. They are also succulent and smooth with grooves. Older plants can have a purplish tinge on the outside and inside of the stem.
Flower Flowering occurs from April–June. The plant produces vibrant, yellow clusters of daisy-like blooms. Green bracts enclose each flower.

Livestock Toxicity

Cressleaf groundsel is toxic to livestock when present in forage grazing systems, or in stored feeds (e.g., dry hay or ensiled forages). Harvesting and drying the forage does not eliminate the threat to livestock. Cressleaf groundsel produces pyrrolizidine alkaloids, secondary metabolites that produce a toxic compound that negatively impacts liver function, resulting in liver disease via necrosis. When assessing poisoned livestock, clinical symptoms may include, but are not limited to:

• lack of appetite
• loose stool
• anorexia
• incoordination
• sensitivity to light (in severe cases)
  (Bildfell, 2024).

Consumption of cressleaf groundsel has also been linked to abortions in grazing livestock, specifically cattle.

It should be noted that livestock rarely seek out this plant in mixed-species pastures, as the coarse woody stem is not palatable. Increased consumption rates of cressleaf groundsel are often associated with a reduction in pasture availability (e.g., drought, overgrazing) and when offered in stored and processed feedstuffs where animals are unable to effectively sort out the toxic weed. Ensiling the forage may reduce but will not eliminate the concentration of the toxins. In hay fields with high concentrations of cressleaf groundsel, baling and disposing of the hay may be a last resort effort to reduce further risk.

When comparing livestock species, cattle tend to be the most susceptible to the negative effects of cressleaf groundsel, with horses being intermediate, and small ruminants being the least susceptible. Sheep and goats are the least susceptible, as they are more selective in their grazing and feeding behaviors than cattle. In general, sheep and goats are more resilient given their increased metabolism rate compared with cattle and horses (Kolrep, et al., 2017) and require 20 times more plant material to be consumed before fatalities occur (Bildfell, 2024). Additionally, Knight and Walter (2001) demonstrated that cattle grazing fresh, green plants that consumed 4%–8% of their body weight over a short period (1–2 days) or approximately 0.1% of their body weight over an extended period (20 or more days) both resulted in animal death. In horses, neurological issues are most often reported, mainly incoordination. The concentration of cressleaf groundsel horses need to consume to demonstrate clinical signs is not well established.

Control of cressleaf groundsel growth is the best management strategy to safeguard animal health. Animals demonstrating clinical signs of cressleaf groundsel toxicosis seldom recover. Even if animals do not show clinical signs after consumption, complications associated with liver disease often lead to secondary challenges, resulting in decreased animal performance or, in severe cases, death. When cressleaf groundsel toxicosis is the suspected cause of death, a necropsy performed by a veterinarian is recommended for confirmation.

Control

Cressleaf groundsel is easiest to control when it is in the rosette stage, before bolting or flowering. Scouting early—late October–early November—is paramount when deciding how to manage cressleaf groundsel.

Control in Grass Pastures/Hay

Since cressleaf groundsel is toxic to livestock, it is important to scout and identify the plant. Once spotted, a few options are available for control.

Mowing can be an effective way to keep cressleaf groundsel from going to seed. To avoid risks to livestock, mowing is most effective when the plant is just a few inches tall and less than several inches in diameter.

With chemical control, applying 2,4-D or 2,4-D + dicamba in late October through early November can prove successful. An amine formulation is suggested when sensitive broadleaf vegetation is nearby; otherwise, a low-volatile ester formulation provides greater control. More than one application may be necessary for complete control.

A premix of aminopyralid + 2,4-D (GrazonNext HL) can provide excellent control in hay fields, but, as always, check and follow label restrictions for grazing or mowing (Sellers et al. 2019).

Control in Alfalfa or Grass/Alfalfa Hay Fields

Many herbicides effective on cressleaf groundsel can injure legumes. The most effective herbicide treatments in legume hay or alfalfa fields are:

• Sencor 75DF (1.3 pounds per acre) or Velpar (2–3 quarts per acre)
  Applied in late February when alfalfa is still dormant. These herbicides can only be applied to established alfalfa (more than one year old). Sencor can be used in fields that have established grasses in addition to the alfalfa. Do not use Velpar in fields with desirable grasses or fields that will be rotated to another crop within the next two years.
• Pursuit (2.16 ounces per acre)
  May suppress groundsel when applied in late fall or early spring. Fall applications are likely to be most effective. Plants should still be in the rosette stage and less than 3-inches tall at the time of application. In the spring, apply during periods of relatively warm weather with daytime temperatures above 60 degrees Fahrenheit and nighttime temperatures above 50F. Include the proper spray adjuvants per the herbicide label. Pursuit can be used in seedling or established alfalfa, but alfalfa seedlings must have at least two trifoliate leaves at the time of application. Do not use this treatment where desirable grasses are present.
• Glyphosate
  Can be applied as a spot treatment in the spring in any legume or legume/grass hay field. This treatment will injure or kill all vegetation in the treated area and should be used only when all other control measures have failed.

Control in No-Till Corn and Soybeans

Adding glyphosate at 1 quart per acre (30 ounces per acre with Roundup PowerMax 3) and an ester formulation of 2,4-D at 1 quart per acre to fall spray applications has proven to give good control of cressleaf groundsel. Applying glyphosate and 2,4-D with a premix of chlorimuron ethyl and tribenuron methyl (i.e. Canopy EX or Cloak EX) has excellent control in a fall burndown with residual control. If applying before a corn rotation, simazine can also provide excellent control at 1 lb per acre + 2,4-D (Lake & Hager, 2009).

If unable to complete a fall application, early spring burndowns before cressleaf groundsel has grown out of the rosette stage can still be provided with glyphosate and/or 2,4-D.

Control in Winter Wheat

Apply a mixture of 2,4-D and either dicamba or Harmony Extra to control cressleaf groundsel in winter wheat. It is best to apply in the early spring when the plants are still small in diameter.

Additional Resources

• OSU Weed Management
  (u.osu.edu/osuweeds)
• Packera glabella (Poir.) C. Jeffrey.
  (plants.usda.gov/plant-profile/PAGL17)

References

Bildfell, R. (2024). Pyrrolizidine alkaloidosis in animals. Merck Manual.
merckvetmanual.com/toxicology/pyrrolizidine-alkaloidosis/pyrrolizidine-alkaloidosis-in-animals

Lake J. T., & Hager A. G. (2009).Herbicide selection and application timing for control of cressleaf groundsel (Packera glabella). Weed Tech 23(2):221–224.
researchgate.net/publication/250056160_Herbicide_Selection_and_Application_Timing_for_Control_of_Cressleaf_Groundsel_Packera_glabella

Knight, A. P., & Walter, R. G. (2001).    A guide to plant poisoning of animals in North America. Teton New Media.
emt.oregonstate.edu/sites/agscid7/files/emt/endophyte-lab/clinical-research/15.pdf

Kolrep, F., Numata, J., Kneuer, C., Preiss-Weigert, A., Lahrssen-Wiederholt, M., Schrenk, D., & These, A. (2018). In vitro biotransformation of pyrrolizidine alkaloids in different species. Part I: Microsomal degradation. Toxicokinetics and Metabolism, 92,1089–1097.
link.springer.com/article/10.1007/s00204-017-2114-7

Sellers, B., Devkota, P., & Ferrell, J. A. (2019). Cressleaf groundsel (Butterweed) identification and management in pastures [Fact sheet]. University of Florida.
edis.ifas.ufl.edu/publication/AG406

Originally written by Mark M. Loux, PhD, Weed Science Extension Specialist, Ohio State University Extension; William P. Shulaw, PhD, Extension Veterinarian, Beef/Sheep, Ohio State University Extension; and Jeff M. Stachler, Extension Weed Program Specialist, Ohio State University Extension.