I’ve had a number of questions regarding the identity of the “yellow weed” in fields. It is seemingly everywhere, especially in fields not yet planted to soybeans. Many people notice the large yellow field along northbound Interstate 65, just before the Boone County 4-H Fairgrounds.

This weed in question is not a mustard, as many people think, but rather a member of the daisy and aster family (Asteraceae/Compositae). In the past mustards were responsible for turning fields yellow. For the past several years it has been ragworts and groundsels doing the work, according to Glenn Nice, a Purdue University weed specialist.

In his travels throughout the state, the weed scientist has been seeing large amounts of cressleaf groundsel.

Many people previously knew them as Senecio species, but they are being placed in the Packera genus (USDA), Nice said. In Indiana we generally have cressleaf groundsel (P. glabella), a winter annual. Occasionally we see golden ragwort (P. aureus) in Indiana which is a perennial. Other than one being an annual and the latter being a perennial, cressleaf groundsel will have a thick hollow stem and golden ragwort will have slender stems, Nice said.

The most common- name is cressleaf groundsel. Other common names for the same weed are groundsel, ragwort, and butterweed. It is not nearly so toxic as a related Senecio species out west.

Seed heads can look like small dandelion seed heads. Cressleaf groundsel can be told apart from mustards by counting the petals. Looking close-up at the flowers, see if they look like a miniature “daisy-type” flower. Mustards have four petals per flower, cressleaf groundsel will have seven to 12 petal like ray flowers (daisy-like). Common groundsel can be found along roadsides, in pastures, and in wet nutrient rich areas. It grows best in cool wet conditions and will die out in periods of hot and dry conditions, as is often found in an Indiana summer.

Packera spp. species can be toxic to cattle and horses. Cressleaf groundsel, not as toxic as its cousin to the West, tansy ragwort (Senecio jacobaea), can still produce toxic alkaloids. Poisoning is most often a chronic, taking several weeks to show symptoms. Senecio (Packera) poisoning is called “seneciosis” or “pictou disease”. Symptoms in cattle can range from scaly noses and rough coats to listless, and a decreased apatite with digestive problems (diarrhea or constipation). In severe cases, cattle may be jaundiced and/or photosensitive. Calves can develop swollen jaws. Horses can become nervous and have the “sleepy staggers,” bumping into objects or becoming entangled in fences. Long term exposure can cause liver damage.

To prevent seneciousis learn to identify Packera spp. species in the pastures and in hay. Remove contaminated hay and avoid feeding on senecio infested pastures.

Learn more:

For information on the control in soybean and corn fields see the article “What Do We Do About the Yellow Fields?” at www.btny.purdue.edu/weedscience/2006/GroundselControl06.pdf.

WHAT TO USE:

Metsulfuron methyl , sold under the brand names Cimerron and Ally, has been reported to control cressleaf groundsel in grass pastures. The use of 2,4-D in the fall or early spring while the plant is still in the rosette stage is a cost effective control method. However, consistency of control begins to drop when cressleaf groundsel begins to bolt.

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