Posted on September 12, 2009 - by mckenzie

Noxious Weeds Part II: Leafy Spurge

Leafy Spurge

Leafy Spurge, also known as Wolf’s Milk, or Wolf’s-milk is a flowering plant found in North America, but native to Eurasia. It is classified as an invasive species by the United States Department of Agriculture.

Leafy spurge is characterized by plants containing a white milky sap and flower parts in three’s. Leafy spurge is an erect, branching, perennial herb 2 to 3½ feet tall, with smooth stems and showy yellow flower bracts. Stems frequently occur in clusters from a vertical root that can extend many feet underground. The leaves are small, oval to lance-shaped, somewhat frosted and slightly wavy along the margin. The flowers of leafy spurge are very small and are borne in greenish-yellow structures surrounded by yellow bracts. Clusters of these showy, yellow bracts open in late May or early June, while the actual flowers do not develop until mid-June. 

Leafy spurge displaces native vegetation in prairie habitats and fields through shading and by usurping available water and nutrients and through plant toxins that prevent the growth of other plants underneath it. Leafy spurge is an aggressive invader and, once present, can completely overtake large areas of open land. 

Leafy spurge tolerates moist to dry soil conditions but is most aggressive under dry conditions where competition from native plants is reduced. It is capable of invading disturbed sites, including prairies, savannas, pastures, abandoned fields and roadside areas. 

Leafy spurge was transported to the U.S. possibly as a seed impurity in the early 1800s. First recorded from Massachusetts in 1827, leafy spurge spread quickly and reached the Western United States within about 80 years. 

Control:

Biological control agents (several stem/root boring beetles, a shoot tip gall midge, a stem boring moth, and 3 root/defoliating flea beetles) have been inconsistent in Idaho. Sheep and goats have been used to check the rate of spread of leafy spurge. Herbicides are available for control.

For more information, click to visit Idaho’s Virtual Field Guide presented by the Weed Awareness Campaign.