Yellow Weeds in my Pastures?



News Column
By: Chad Gulley
County Extension Agent–Ag/NR
Smith County

What are these yellow flowers in my pasture?

Have you noticed yellow flowers growing in your pastures lately? There are several plants with yellow flowers but the Texas Groundsel (Senecio ampullaceus) and Buttercups (Ranunculus spp.) are the most abundant right now.

The Texas Groundsel is a cool-season annual herb.  It can grow to 12 to 30 inches tall.  The plant often looks whitish with hair but some can be hairless.  The unlobed, clasping leaves gradually reduce in size toward the top of the plant.  Showy yellow flowers are produced in the spring.  The seedling or winter rosette often has a purplish cast to the underside of the leaves, especially on the midrib.

The Texas Groundsel is primarily found in the eastern half of Texas.  It is abundant in sandy soils.  It can also be seen in areas of freshly cleared forest lands.

The Texas Groundsel is considered a toxic plant.  The toxic agent of this plant is still not determined, nor have experimental feeding trials proven its toxicity.  As with any toxic plant, identification is important.  Also, if cattle have adequate forage, hay or supplementation, they will not readily consume this or other potentially toxic plants.

Cattle are more likely to consume the young plants while they are still in the rosette stage in late fall and winter.  Llamas seem to be more sensitive to the plant or less selective grazers than cattle.  Cattle consuming this plant develop clinical signs and lesions typical of pyrrolizidine alkaloid poisoning as seen in other Senecio species.  Clinical signs of cattle and llamas that have consumed this plant include anorexia, depression, weight loss, aggression, and even death due to liver failure.

Buttercups may be an annual or perennial with 18 different species of this plant.  Buttercups have stem leaves that are alternate, with palmlike veins, and are deeply lobed or dissected. The basal leaves usually have a distinctly different shape.  Flowers are arranged in fan shaped clusters. They usually have five glossy yellow petals and give rise to a small, dry fruit.

All buttercup species grow in wetter soils.  Buttercups can be found growing in seeps, mud flats, and in areas along ditches and roadsides with shallow water.  Buttercup species growing in essentially all vegetational regions of Texas but are predominantly seen in the eastern portion of Texas.

All species are thought to contain a glycoside at various concentrations that is converted to protoanemonin, which acts as a blistering agent. The levels of glycoside increases greatly as the plants mature and reach the flowering stage.

Because protoanemonin is not stable, the plant is not a problem in hay. Although the toxin content varies widely within and among species of buttercup, a large amount of plant material is usually required to cause clinical signs with the species growing in Texas.

The signs of poisoning are those of severe gastrointestinal irritation and include: red and/or ulcerated oral tissues, salivation, blood-tinged milk, diarrhea, abdominal pain, depression or excitation, convulsions, and death.  Most cases of buttercup poisoning in Texas are not life threatening.

How do I control these plants in my pastures?  There are several methods.  In light infestations, hand removal or spot spraying may eliminate the presence of this weed.  In heavy infestations, a broadcast application of a selective herbicide may offer adequate control.

One way to control these and other weed species in your pasture is to stay on top of your fertility program.  Weeds have a hard time competing with a good, healthy dense stand of grass.  Annual weeds are easily controlled in the seedling stage.  Because these are cool-season annuals, the plant will germinate in the fall, grow all winter, then flower and produce seed as we enter late spring to early summer before the plant dies.  Again to reiterate, livestock will not readily consume either of these plant species if they have adequate forage.   As with many weed species, they rob our grasses in pastures and hayfields of much needed water and nutrients.

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