By DOUG GRAVES
Ohio Correspondent

GREENVILLE, Ohio — From a distance, the bright yellow flower looks like nothing more than a patch of canola. But upon closer examination, this long-stemmed plant is a highly-toxic weed, and it’s appearing in more Ohio fields each year.

The toxic weed is called the cressleaf groudsel. It appeared in just four Ohio counties by 1990. Just recently, it was spotted in Darke and neighboring counties.

“I’ve been getting numerous calls, mostly from livestock producers, about this weed in many of the no-till or minimum tillage fields in the area,” said Steve Foster, extension specialist in Darke County. “This weed looks harmless, but it’s quite toxic to livestock.”

According to Foster, the weed species is relatively new to Ohio, having been recorded in OSU herbarium samples from only four counties prior to 1990. Since that time, cressleaf groundsel has spread to other parts of Ohio and is included in Ohio’s Noxious Weed List because of its poisonous characteristics.

“This weed germinates in the fall,” he added. “Farmers need just to kill it by simply mowing it. It is found mostly in hay fields.”

Foster said although he hasn’t received any notices about animal deaths in his county from the weed, farmers should heed the warning that it is highly toxic to both man and animal.

How to spot it

Cressleaf groundsel is a member of the Aster/Composite family. It goes by many other names, including butterweed, yellowtop, golden ragwort and yellow ragwort. It has a winter annual life cycle, meaning it emerges in the fall and flowers in the spring (after May 10). Cressleaf groundsel reproduces only from seeds. Each plant produces thousands of seeds that are readily moved by wind currents. It grows well in many different environments, including saturated soils.

The stems of cressleaf groundsel are hollow and grooved, and the entire plant is hairless. The flowers are similar to those of other species in the Aster family, having ray (outside) and disk (center) petals. Both petals are bright yellow in color, and the ray petals are 0.33 to 0.75 inches in length.

Individual flowers are grouped together in clusters, and there are usually several branches of flowers. Nearly all species of Senecio are considered potentially toxic plants because they contain compounds called pyrrolizidine alkaloids (PAs). These are metabolized in the liver to other compounds that are toxic, primarily to the liver cells.

The PAs are found in the plant through the growing season, but appear to be at their highest levels when the plant is in the bud-to-flower stage. The flowering portions of the plant and the youngest tissues generally contain the highest concentrations. PAs are not destroyed by the haymaking and curing process.

Danger to animals?

Ensiling of forages may reduce the concentration of PAs, but will not entirely eliminate them. According to Foster, sheep are considered more resistant to the effects of PAs than cattle and horses, and have been used in some areas to control the plant.

“Under typical grazing conditions in Ohio, it is unlikely that animals will consume significant quantities of the weed because of the availability of higher quality, more palatable forages,” Foster said. “Poisoning could result under unusual conditions, such as drought, where good quality forage is not available.

“Hay containing significant amounts of the plant may pose a greater risk. Poisoning usually occurs as a result of consumption of the plants over several days to several months. Because the effect on the liver is cumulative, signs of poisoning can occur weeks to months after consumption of the plant ceases.”

He added, “The signs are directly attributable to liver degeneration and failure. Affected animals usually show depression and loss of appetite initially, and progress to neurological signs with head pressing, aimless walking, poor coordination and rectal straining.

“At postmortem examination, the liver will usually be shrunken and fibrotic, with grayish blue to yellowish discoloration. Treatment is only symptomatic and not usually successful once signs appear.”
Management

While there are no confirmed deaths attributed to this toxic weed, liver lesions suggestive of PA poisoning have been observed on rare occasions. Although the presence of the occasional plant in a hay field is probably not cause for concern, producers are advised to avoid harvesting areas of the field that have high concentrations of the plants. Subsequent cuttings during that growing season may be safe, although the plant may be present again in the fall.

The goals of a cressleaf groundsel management program should be to minimize its occurrence in areas where it could poison livestock, and prevent seed production to reduce future infestations. This can be accomplished through mowing in the spring, where size of the field or groundsel patches allows.

To minimize the risk to grazing livestock and reduce the amount of groundsel in hay, mow often enough to prevent the plant from becoming more than several inches tall. This strategy can also minimize seed production, although small groundsel can still flower and produce seed.

Delaying mowing until the plant is in the bud-to-flower stage will most effectively prevent seed production, but may not minimize the risk of poisoning. The groundsel is not likely to grow again after the first cutting of hay in the spring, but a goal of control strategies should be to prevent it from contaminating the first cutting.

Cressleaf groundsel is most easily controlled with herbicides in the late fall or early spring. Most plants will have emerged by late October and will be small enough in fall or early spring to be controlled with 2,4-D or other low-cost treatments.

Plants become considerably more difficult to control once they have started to grow in the spring and are more than several inches in diameter.

Cressleaf groundsel should be controlled by the flower stage in roadsides and fallow areas, and neighboring corn, soybean, and wheat fields. Movement of seed from mature groundsel plants in these areas can be a source of new infestations in nearby pasture and hayfields.

This farm news was published in the June 2, 2007 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee.