THE FLORIDA CATTLEMAN AND LIVESTOCK JOURNAL
Caesarweed Management in Pastures
Brent Sellers and Jose Dias
For questions or comments regarding this publication contact: Brent Sellers, University of Florida, IFAS
Caesarweed (Urena lobata; Figure 1), known by many as cocklebur, is a non-native species that is believed to have originated in Asia and has spread throughout most tropical and subtropical areas. Originally, this species was grown in many areas as a fiber crop, but has also been used in herbal medicine. Also, the leaves and flowers are considered a famine food in some areas of Africa. Because it was utilized as a crop species in some areas, a lot of research was conducted on increasing seed production as well as seed germination uniformity, etc.
Caesarweed is generally considered to be an annual species, but in the southern part of the state, it can act like a perennial species. When it does act as a perennial species, spread continues to be through seed production like annual plants as there is not a creeping root system. Individual plants can grow from 1.5 to 10 ft tall with 3-inch diameter stems at the base of the plant. Gray-like colored leaves are lobed and covered with star-shaped hairs. It has been suggested that a single plant can produce up to 600 seeds, but may be more in portions of the state where frost does not occur as these plants can flower and produce seed year-round. Seed are dispersed by animals and humans because of the barbed seed coverings. Anyone who has walked through a Caesarweed patch, or has animals that have grazed this plant in the past is very familiar with the seed.
Caesarweed is becoming more common in improved pastures, and especially in areas where livestock congregate. Most often, we see Caesarweed growing under the drip line of large oak trees as well as under other tree species where light penetration into the understory is limited. It will also grow in open pastures, especially in areas that are overgrazed or highly disturbed. Although light is not a requirement for germination, the absence of grass forage to compete with Caesarweed seedlings often leads to rapid establishment of plants. Seed germination typically occurs within the top 2.5 inches of the soil surface, but can occur as deep as 3.5 inches. Soil pH and temperature have little impact on Caesarweed germination, indicating that it can germinate and establish on a wide range of soils throughout Florida. Considering that Caesarweed seed is extremely sensitive to water stress, germination is usually delayed until the rainy season begins in June.
Although cattle and other livestock will readily eat Caesarweed, they typically only eat the most tender, new growth of the plant. Plants that have been grazed, or mowed for that matter, typically have a larger number of branches compared to non-mowed/non-grazed plants giving it a shrub-like appearance. Regardless of whether a plant has been grazed or not, the presence of tall or shrubby Caesarweed plants could affect forage production and persistence in some situations. Remember that bahiagrass does not tolerate shade very well; therefore, the presence of Caesarweed could impact the longevity of the bahiagrass stand in addition to reducing forage yields. This makes control of Caesarweed, in some instances, extremely necessary.
Our research has indicated that Caesarweed is sensitive to many of the pasture herbicides. We treated 6 to 7 ft tall Caesarweed plants at different locations over a 2 year period with Pasturegard HL at 16 or 32 oz/acre, Weedar (2,4-D amine) at 32 or 64 oz/acre, Remedy Ultra at 16 or 32 oz/acre, or Milestone at 7 oz/acre. Our sprayer was calibrated to apply 20 gallons of spray solution per acre. All treatments, except Milestone, provided greater than 90% control 30 days after treatment; Milestone provided only 70% control (Figure 2). By 60 days after treatment, all treatments resulted in 100% control of Caesarweed (Figure 3). New seedlings did occur in all plots, but we had fewer plants in plots treated with Milestone one year after treatment.
Caesarweed, although it can become quite woody, is susceptible to many of the herbicides readily available for weed control in pastures. Although we applied 2,4-D and Milestone separately in our studies, the combination of Milestone and 2,4-D in GrazonNext HL should provide excellent Caesarweed control, regardless of growth stage. Remember, to obtain effective control of any weed species, they must be actively growing. So, avoid herbicide applications during drought and potential frost events.
Figure 1. Representation of Caesarweed growing in the understory of planted pines. Photograph by Brent Sellers.
Figure 2. Response of Caesarweed to Pasturegard HL (PTG), 2,4-D amine (Weedar), Remedy Ultra, and Milestone (MLT) at 30 days after treatment. Bars with different letters indicate significant differences between treatments.
Figure 3. Response of Caesarweed to Pasturegard HL (PTG), 2,4-D amine (Weedar), Remedy Ultra, and Milestone (MLT) at 60 days after treatment.