Weeds, Weeds Everywhere!

The hot days of summer really bring on the growth of weeds in pastures and gardens, making it important to recognize and control weeds before they mature, flower and produce seed to further their spread.

A particularly aggressive non-native noxious weed is leafy spurge (Euphorbia esula). Some taxonomists (Webber) also name it as Tythimalus uralensis. Native to Eurasia, leafy spurge was first recognized in North America in 1827, and is now in most states, continuing to spread. In a Colorado survey in 2002, it was estimated to infest almost 74,000 acres. As an invasive species, it causes great economic loss because it displaces nutritious grasses and other plants, depriving livestock of food. Once leafy spurge becomes established in an area it is also expensive to control with herbicides.

Leafy spurge is a perennial that emerges in April and May, producing flowers and seeds by June. When in bloom it is quite showy, and some may be tempted to think it is a desirable wild flower! It is an erect plant growing to three feet tall, with bluish-green leaves up to four inches in length. A milky sap is present in the stems and leaves that can be a skin irritant. At the tops of the stems, yellowish-green bracts are often mistaken for the flowers. In fact the true flowers are small paired structures (cyathium) situated between the bracts. (The poinsettia is a member of the same family as leafy spurge, and has red or white bracts.) Seeds are produced in capsules which when dry, open explosively propelling seeds as far as 15 feet. It is common to see leafy spurge along river banks and irrigation ditches because the seeds float and can be carried to new locations by water. Once a seed germinates, it quickly develops an extensive root system with buds that enables the leafy spurge to spread in subsequent years.

Horses and cattle will not readily eat leafy spurge because of its taste, and the irritant sap can cause excessive salivation and diarrhea. Sheep and goats will readily graze the plants making them useful biological controls. Since some of the seeds of the leafy spurge pass through the digestive system of sheep and goats and remain viable, it is important to hold the sheep and goats for a week in a corral, or in the same area after they have eaten all the plants to ensure they do not spread the seeds in new areas via their droppings.

Early recognition of leafy spurge improves the chances of effectively controlling it. Once established in a pasture, it requires a combination of methods to control the plant. A variety of herbicides are effective for controlling leafy spurge if they are applied repeatedly at the appropriate times of the plants growth. See Fact Sheet # 3.107 - Leafy Spurge.

In addition to herbicides and sheep and goats, a variety of flea beetles have been developed that will selectively feed on leafy spurge, and hold promise as an effective biological control. Using a combination of control measure and being persistent makes it possible to effectively control leafy spurge.

Photographs: Taken by Tony Knight; close-up of bract structures and biological control of leafy spurge using goats.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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This page updated:  July 18, 2007