THE FLORIDA CATTLEMAN AND LIVESTOCK JOURNAL
Cressleaf Groundsel/Butterweed Infestations on the Increase in Pastures
During the past couple of years we have seen an increase in the number of calls of a succulent plant that produces many yellow flowers. In some cases, the infestation has been so high that the pasture looks like a sea of yellow in April and May. In row crops we think of wild radish when we see a sea of yellow, but the plant infesting pastures during the late winter and early spring is commonly known as butterweed or cressleaf groundsel (Packera glabella formerly known as Senecio glabellus).
Butterweed is a winter annual, with emergence beginning as early as November in some areas of the state. It tends to prefer moist soils, so presence of the weed in low lying areas in pastures is quite common. It first grows as a rosette, with leaves oppositely arranged on the stem, but it may appear to have whorled leaves as the internode length on the stems tends to be fairly short (Figure 1). Leaves of this plant tend to be deeply lobed, except at the seedling stage when the leaves are nearly entire (without lobes). As the flowering stalk elongates, the stems are ribbed with streaks of red or purple (Figure 2). The leaf arrangement becomes alternate on the succulent and hollow stems. Butterweed is typically not recognized until it begins flowering. Many bright yellow flowers are produced on the stems. Individual flowers, like many of those in the aster family, have both inner (disk) and outer (ray) flowers (Figure 3). Butterweed will have 5 to 15 outer ray petals, which helps differentiate this species from mustards, which only have 4 petals in a cross-like pattern. Seeds are dispersed by wind through a white feathery pappus.
Butterweed is toxic to both cattle and horses. It is known to cause liver disease in cattle with symptoms including listlessness, decrease of appetite, and photosensitization in extreme cases. Horses tend to appear uncoordinated after ingesting the plants and often become entangled in fences and awkwardly bump into objects. Acute liver necrosis and death in 1 to 2 days in cattle occurred when fed 4 to 8% of the animal’s body weight in green plant over a few days. Cattle that ingested 0.15% of a species in the same genus as butterweed for a minimum of 20 days had 100 percent mortality. This equates to a 20-day cumulative dose of 2% of an animal’s body weight of dry plants (Knight and Walter 2001). Also, it appears that this species has been responsible for abortions in cattle, making control of this plant a necessity.
Control of butterweed is successful with 2,4-D during the rosette growth stage. We have observed excellent control of butterweed with GrazonNext or Milestone during any growth stage. Currently, many of these plants are in the rosette stage, which is the best time to control this plant. However, it is common to see plants at all stages of growth in late February to late March. Since 2,4-D has limited residual activity, it is likely that more than one application may be necessary in some situations.
If you have seen this weed in your pastures in previous years, it is extremely important to scout those pastures this winter. Timely herbicide applications will help prevent poisoning from this toxic species. If you have further questions concerning this species, please contact your local county agent.
Reference: Knight, A.P. and R.G. Walter. 2001. A Guide to Plant Poisoning of Animals in North America. Jackson, WY: Teton New Media.
Figure 1. Butterweed rosette in a bahiagrass pasture. This size of rosette is commonly observed in late December to early January, and is often seen when other plants are already flowering. Photo by B. Sellers.