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Management Of Leafy Spurge
Leafy spurge is a creeping perennial that is difficult to control because of the vigorous reproduction by underground stems (rhizomes). This plant contains a milky latex, which is poisonous to cattle causing it to further dominate rangeland. Leafy spurge has been known to establish a monoculture on previously productive rangelands. Early detection and eradication of this species is critical and the most economical method of control.
In Larimer County, leafy spurge is predominately found in course-textured soils, along waterways, irrigation ditches, and riparian areas.
Mechanical Control
Two types of tillage programs - intensive throughout the growing season and fall-only cultivation- have proven useful. The cultivation schedule should be consistent however because leafy spurge recovers quickly from rootstock, and pieces of roots as small as ½ inch long and 1/10 inch in diameter can produce new shoots.
Mowing every two to four weeks will reduce seed production and prevent new infestations to neighbors' properties. However, mowing will provide little long-term control. Handpulling is only effective if the population consists of just a few plants. In addition, the milky latex in spurge can be irritating to the skin.
Chemical Control
The most important thing to remember when applying herbicides is to READ THE LABEL. The label is a legal document. Applying too much of a herbicide could cause injury to desirable plant species and is illegal. Applying too small of a quantity of a herbicide can stimulate weed growth.
At this time, herbicides provide the quickest and most effective method of control for leafy spurge. Small patches of leafy spurge should be managed with herbicides and not biological methods. It is recommended to treat an extra 10 to 15 feet around leafy spurge patches to control spreading roots and seedlings. Eradicating these small patches should be the highest priority of a management program (Lajeunesse et al. 1999).
Current research indicates that effective control is achieved with 2,4-D, Banvel (dicamba), Imazapic (Plateau) and Tordon (picloram). Most herbicides are effective when applied in spring when true flowers emerge (not just bracts). However, timing of herbicides varies and the label should be checked to determine the most appropriate time for application. For leafy spurge, Tordon is the most effective and can be applied at 1 quart/A for three to four consecutive ears. These herbicides can be purchased at an agricultural products supplier (please check the yellow pages for specific stores).
Biological Control
Biological control is most desirable in places where herbicide use is restricted (i.e. riparian areas) or the weed infestation has become extensive enough to make chemical control cost prohibitive. An increasing amount of research has been directed in the use of spurge flea beetles. Data from Colorado State University shows the effective control of leafy spurge with the copper spurge flea beetle (Aphthona flava) used in combination with sheep grazing. During the 1999 season, the Larimer County Weed District distributed various Aphthona species to landowners with significant leafy spurge populations. It is our goal to offer this program for the year 2000 season.
Cultural Control
A healthy plant population is crucial to the control of leafy spurge. Activities such as overgrazing may stress desirable vegetation and thus make them more susceptible to leafy spurge invasion. Also, maintaining fertile soils will assist in a healthy, weed-resistant plant population. Research has shown the most competitive grasses that have been tested were Russian wildrye, pubescent wheatgrass, western wheatgrass, Dahurian wildrye, and little bluestem.
Although leafy spurge is poisonous to cattle, sheep and goats will readily eat this plant, generally preferring leafy spurge to desirable grasses. This is an effective control when used in combination with other methods. Grazing alone has been shown to increase shoot density by stimulating reproduction by rootbuds.