Weed of the Month: Wild Poinsettia

Published: September 22, 2010

Wild poinsettia (Euphorbia heterophylla) is a summer annual weed primarily distributed in the tropical climates of South America but also developing into more of a problem in the southern United States (Jowers et al. 1986; Wilson et al. 1981). In Missouri, we have encountered more of this weed over the past 3 or 4 growing seasons, especially as a weed of soybeans.

Figure 1. Wild poinsettia seedling.

Wild poinsettia seedlings have an egg-shaped cotyledon with the first true leaves arranged oppositely from one another (Figure 1). The first true leaves will be lanceolate in outline and are approximately ½ to 3 inches in length. Once these plants mature the leaves can take on a characteristic poinsettia-like growth habit and often have a dark red spot on the upper surface. Both the leaves and stems are hairy and emit a milky sap when broken. The flowers of these plants occur in clusters at the ends of branches and have no distinct petals (Figure 2).

Figure 2. Mature wild poinsettia plants in flower

Wild poinsettia is capable of germinating under a range of different light, temperature, pH, soil depth, and moisture conditions (Brecke 1995). Brecke (1995) found that wild poinsettia can withstand soil pH ranges from 2.5 to 10 and is capable of germinating from depths of as much as 6-inches 2 to 3 weeks after planting. Wild poinsettia requires very little moisture for germination and has the opportunity to become established under a variety of growing conditions, both in crop and non-crop environments. Wild poinsettia also exhibits a high degree of genetic variability. In one study, researchers found only 40% genetic similarity between 40 different populations of wild poinsettia. (Winkler et al. 2003).

Several researchers have demonstrated that wild poinsettia can cause significant yield losses in soybean. Harger and Nester (1980) found that 8 wild poinsettia plants per meter of row reduced soybean yields by as much as 18% when allowed to compete for 8 weeks during the growing season. Seasonlong competition from this same density of wild poinsettia plants reduced soybean yields by 33%. Similarly, Chemale and Fleck (1982) found that 54 wild poinsettia plants per m2 reduced soybean yields by 50% when allowed to compete for 115 days after soybean emergence.

Based on the literature we have reviewed pertaining to wild poinsettia control with herbicides, it seems that the most effective control of this weed will be achieved with a pre-emergence (PRE) followed by a post-emergence (POST) herbicide program in soybeans. The fairly deep depth of soil from which this weed can germinate can often make PRE herbicides alone ineffective. Some of the more effective PRE soybean herbicides for wild poinsettia include Sencor, Scepter, Valor XLT, and Envive (Willard and Griffin 1993). POST control of wild poinsettia has usually been accomplished with ALS-inhibiting herbicides like Classic or Scepter, with PPO-inhibiting herbicides like Flexstar, Ultra Blazer, or Cobra, or with glyphosate (sold as Roundup and a variety of other trade names). However, when using a POSTonly herbicide program approach, repeat treatments will likely be needed in order to prevent yield loss especially when wild poinsettia populations are high (Brecke 1996). Additionally, selection of wild poinsettia plants resistant to ALS-inhibiting herbicides and glyphosate has been documented in Brazil and other South American countries (Heap 2010), so it is important to be on the lookout for this weed as a potential problem species in the future.

References

Brecke, B.J. 1995. Wild Poinsettia (Euphorbia heterophylla) germination and emergence. Weed Sci. 43:103-106.

Chemale, V.M. and N.G. Fleck. 1982. Evaluation of soybean (Glycine max (L.) Merrill) cultivars in competition with Euphorbia heterophylssa L. in three densities and two periods of occurrence. Planta Daninha 2:36-45.

Harger, T.R. and P.R. Nester. 1980. Wild poinsettia: a major soybean weed. Louisiana Agric. 23:4,5,7.

Heap, I. The international survey of herbicide resistant weeds. Online, Internet. August 11, 2010. Available www.weedscience.org.

Jowers, H.E., J.W. Breman, and J.W. Fletcher. 1986. Effects of several herbicide treatments on wild poinsettia (Euphorbia heterophylla L.) control in soybean. Soil Crop Sci. Soc. Fla. Proc. 45:115-117.

Willard, T.S. and J.L. Griffin. 1993. Soybean (Glycine max) yield and quality responses associated with wild poinsettia (Euphorbia heterophylla) Control Programs. Weed Technol. 7:118-122.

Wilson, A.K. 1981. Euphorbia heterophylla: a review of distribution, importance and control. Trop. Pest Manag. 27:32-38.

Winkler, L.M., R.A. Vidal, and J.F.B. Neto. 2003 Caracterizacao genetic de Euphorbia heterophylla resistente a herbicidas inibidores da acetolactato sintase. Pesqu. Agropecu. Bras. 38:1067-1072.