September 22, 2011

My first encounter with toothed spurge occurred in 1985 when I observed the weed growing in a sugarbeet field near Mitchell. Over the years, it has become a permanent resident on the farm, part of the weed flora when fields have been planted with corn, dry beans, onions, potatoes, or sugarbeets. Over the last 10 years, populations have increased and it has shifted from a novelty weed to one growers in western Nebraska are interested in controlling.

Description and Growth Habit

Tooted spurge, also known as wild poinsettia, is native to the eastern U.S. and Mexico. Its scientific name is Euphorbia dentate. This plant is classified in the spurge family which includes leafy spurge—a noxious weed in rangeland, spotted spurge—a troublesome weed in turf, and cushion spurge—a flower garden spring perennial. Toothed spurge is considered a summer annual and reproduces by producing seeds that germinate in the spring.

As the name suggests, the leaves of the plant are shaped like a lance, have toothed margins, and all plant parts contain a milky sap that becomes evident when leaves or stems are broken. In this area, toothed spurge can attain a height of 2 to 3 feet, is more prevalent in spring-planted rather than fall-planted crops, but can also be found growing in range, pasture, and along roadsides. Toothed spurge seeds are borne in a three-lobed capsule. Seeds are oval in shape, dark brown to black in color, approximately 1/8 inch long, and can remain viable in the soil for many years. Seeds are an important food for birds, especially mourning doves, which may help spread weed seed.

Toothed spurge is small in stature compared to many of the weeds found in western Nebraska, such as sunflowers, kochia, lambsquarters, and pigweeds.

This weed does have a distinct advantage over other weeds: it has a degree of tolerance to glyphosate (Roundup®). As glyphosate use has increased, so has the presence of toothed spurge. Glyphosate kills its neighbors and leaves a nitch for toothed spurge to flourish. Research has shown a single application of glyphosate in sugar beet will only control 50% to 60% of the toothed spurge; two glyphosate applications can increase control to 70% to 80%. A reliance on only glyphosate for weed control has allowed toothed spurge to increase.

A second advantage for toothed spurge is that many of the non-glyphosate herbicides (Dual Magnum, Eptam, Norton, Outlook, Prowl, Sonalan, and Warrant) provide limited toothed spurge control. Fortunately, there are herbicides used in western Nebraska that will provide effective toothed spurge control, and in Roundup Ready sugar beets and corn, these herbicides can be used with glyphosate (Table 1).

A successful control program for toothed spurge will take several years and require controlling the weed in each crop in a cropping rotation. Research suggests that the weed declines with no-till cropping systems compared to preplant tillage before planting.

Robert Wilson, Extension Weed Specialist
Panhandle REC, Scottsbluff