Attractive, yellow-flowered weeds may harm livestock

The delayed planting this spring has allowed many weeds to survive longer and get larger compared to other growing seasons. Currently, some fields have weeds with striking yellow flowers. In fact, some of these fields have so many yellow-flowered weeds that it resembles a new crop in the area. Agronomists call this yellowed-flowered plant cressleaf groundsel because the leaves resemble those of garden cress and watercress. Butterweed is another common name, as are yellowtop, golden ragwort and yellow ragwort. Packera glabella (Poir.) C. Jeffrey is the scientific name for cressleaf groundsel, but one may also see the older taxonomic name, Senecio glabellus. Groundsel belongs to the Aster/Composite family, which includes dandelions and sunflowers. Some people may mistake groundsel as wild mustard, such as yellow rocket, but mustard plants are in the old taxonomy family of Cruciferae because their flowers are four petals in a cross shape. Flowers in the aster family are daisy-like, and seed heads look like miniature dandelion puffballs. Daisy and groundsel have two types of flowers. The center area of the flower head is a composite of hundreds of little flowers called disk flowers; and the perimeter of the head has a ring of big petals surrounding the disk flowers called ray flowers. Seeds form from the disk flowers. Cressleaf groundsel is a winter annual; it emerges in the fall and overwinters as a rosette of leaves. Often, these leaves will be deep purple on the underneath side. In the spring, the main stem will elongate and produce flowers at the end of branches and the top of the main stem. The main stem is a thick stalk that has reddish streaks giving a purplish tint. Leaves on the main stem will be hairy, irregular in shape, and lobe-like, with deep cuts to the midrib. Groundsel reproduces only from seeds. However, it is a heavy seed producer, and each plant may produce hundreds of seeds that are blown by the wind, like dandelions. The seeds can remain viable in soils for many years. Cressleaf groundsel is a native to the U.S., ranging from Texas east to Florida, up the Atlantic Coast to Virginia, and west to Nebraska. In recent years, it has moved northward from southern Ohio. It is generally found in wastelands, pastures, fence rows and alongside roadsides, but has been become more common in no-till and reduced-tillage fields. Groundsel contains compounds that form toxins in the liver of livestock. These compounds are not destroyed by the haymaking and curing process, and ensiling may only reduce the concentration. Cattle and horses are more susceptible to the toxins than sheep. However, under typical grazing conditions, it is unlikely that livestock will consume significant quantities because of the availability of other higher quality, more desirable forages. Livestock affected by the toxins will have signs of liver degeneration and failure. Symptoms initially include depression and loss of appetite and, if severe, will progress to neurological signs with head pressing, aimless walking and staggering. Because of the plant's toxicity, it is included as one of the 31 weeds on Ohio's Department of Agriculture Noxious Weed List (http://codes.ohio.gov/oac/901%3A5-37). Property owners need to be responsible and control this weed in livestock production areas. Herbicides used by farmers in cultivated fields will control cressleaf groundsel in most situations. For pastures, control is more difficult and may require a combination of herbicides and mowing. Herbicides are available for alfalfa but are more difficult to manage. At this time, areas in hay fields that have groundsel should not be harvested with the first cutting. These areas should be mowed off. Since it is an annual, it will not be a problem for the second cutting. Typical broadleaf herbicides are effective in lawn situations and would eliminate groundsel. In other landscape settings, plants may have to be removed by hand. The weed with bright yellow flowers will soon disappear as farmers apply herbicides and plant crops over the next few weeks. Additional information on cressleaf groundsel may be found at https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/7/3461/files/2014/04/Cressleaf_groundsel_article_-_p-zna9t9.pdf Lentz is Extension educator for agriculture and natural resources for Ohio State University Extension-Hancock County.