Leafy Spurge Control
Leafy spurge is a deep-rooted perennial that ranges in height from 6 inches to 36 inches (15 to 91 cm). Its greenish-yellow inflorescences are borne in an umbel pattern, and it typically blooms from May to October. Each umbel supports seven to 10 groups of tiny, inconspicuous flowers, subtended by four crescent-shaped glands and two conspicuous greenish-yellow bracts. The bluish-green leaves of leafy spurge are usually alternate except for those located immediately under the inflorescence. These are in a whorled arrangement. Another characteristic is the two kinds of leaves present on the stem: leaves located on the lower half of the stem are scale-like, while those on the upper portion are linear to oblong. Leafy spurge has milky white sap that will flow from any part of the plant following injury. This sap may cause severe irritation to human skin and is reported to cause blistering and hair loss on the legs of horses in heavily infested pastures.
The most conspicuous features to look for when distinguishing leafy spurge from other plants are its greenish-yellow inflorescences; alternate, linear to slightly oblong or scaly leaves; and milky-white sap that flows readily upon injury to the plant. Leafy spurge should be accurately identified before attempting any control measures. If identification of the species is in doubt, the plant's identity should be confirmed by a knowledgeable individual and/or by consulting appropriate books.
Native to Europe and temperate Asia, leafy spurge currently is found throughout the world with the exception of Australia. It was probably introduced into the United States as a contaminant in imported grain. Since its introduction, the plant has become a serious management problem, particularly for the north and central plains states. States with the greatest infestations include Colorado, Idaho, Minnesota, Montana, Nebraska, North Dakota, Oregon, South Dakota, Wisconsin and Wyoming. The plant has been documented in Missouri from Grundy and Chariton counties, but it is probably more widespread in northern Missouri than records indicate.
Leafy spurge is adapted to a wide range of soil moisture conditions from moist to dry. However, it is especially aggressive in very dry situations where competition from native species is less intense. Areas most sensitive to leafy spurge infestation include pastures, roadsides, abandoned fields, railroad ballasts, disturbed and undisturbed mesic to dry prairies, and possibly open natural communities such as savannas. It is not a common invader of tilled cropland sites.
Leafy spurge emerges in the early spring when temperatures still fluctuate around freezing. Seedlings at this time may be deep red or purplish in color. As the temperature rises, the stems grow rapidly and, if the plant is over a year old, flowers may appear as early as May. After four to six weeks, each stalk may produce and disperse more than 200 seeds with a germination rate of 60 to 80 percent. However, in spite of this impressive germination rate, the key reproductive capabilities of leafy spurge remain underground. The root system of the plant is very extensive. Some roots may penetrate to a depth of 12 feet. Vegetative reproduction from both crown buds and root buds explain not only the persistence of this weed, but the difficulties encountered in eradicating it as well. Even if the foliage of the plant is removed or destroyed, the living root tissue will regenerate new shoots, and the new shoots can emerge from buds located anywhere along the length of the root.
Effects Upon Natural Areas
If leafy spurge becomes well established in Missouri, it will probably threaten mesic to dry prairies. Forbs and native grasses can be completely displaced by leafy spurge in a few years if the infestation is left unchecked.
Leafy spurge is not a widespread species in Missouri at present. It does occur in at least two counties of northern Missouri. Great Plains states northwest of Missouri report expanding populations of this weed, and there is every reason to believe that it will continue to spread in our area.
Leafy spurge is well established in the central plains states where much time and effort is spent trying to find a control. Most agree that the key to stopping this pest revolves around the ability to destroy its root system. The best way to inhibit this nuisance plant from becoming as destructive as purple loosestrife and multiflora rose is to recognize it as a pest now; treat the initial invading populations and prevent it from spreading any further. The sooner you attack leafy spurge--in its first year if possible--the better the chances of controlling it. All methods below may need to be repeated for five to 10 years.
Whatever the treatment, it is important to remember that leafy spurge cannot be controlled with a single herbicide application. At Devil's Tower National Monument in Wyoming, managers have been spraying on an annual basis for about 20 years and have significantly reduced but not eradicated leafy spurge populations.
Several chemicals have been used for leafy spurge control. These include picloram, 2,4-D, dicamba and glyphosate. Picloram is thought to be the most effective; but, due to its expense, it is often mixed with 2,4-D to treat large infestations. Picloram's residual activity in the soil may harm non-target species in natural communities. Biannual application of 2,4-D alone will probably prevent seed production and limit the spread of leafy spurge. It is unlikely to reduce the size of the original infestation, however.
For top growth control, the herbicide 2,4-D amine can be sprayed on the foliage in a 25-percent solution (1 part 2,4-D in four parts water) twice a year. The most effective time to apply the herbicide is mid- to late June when the true flowers (not the bracts) begin to appear. The second spray application should be made early to mid-September when fall regrowth has begun but before a killing frost occurs.
The nonselective herbicide Roundup (a formulation of glyphosate), sprayed on leafy spurge foliage as a 33-percent solution (one part Roundup in three parts water), will provide 80- to 90-percent top control if applied between mid-August and mid-September. A follow-up treatment with a 25-percent solution of 2,4-D amine between mid-June and mid-July of the following year is necessary to control seedlings.
Apply the herbicide with a hand-sprayer until the spray coverage is uniform and complete. Do not spray so heavily that herbicide drips off the target species. Roundup is a nonselective herbicide that kills grasses and broadleaf plants. 2,4-D is a selective herbicide that kills broadleaf plants, but not grasses. Try to spray leafy spurge only, and carefully avoid contacting non-target species. Native non-target plants will be important in recolonizing the site after leafy spurge is controlled. The herbicide should be applied while backing away from the areas to avoid walking through the wet herbicide. By law, herbicides only may be applied according to label instructions.
Prescribed burning and herbiciding
Fire in conjunction with herbicides may be more effective than either method alone. Burning stimulates vegetative growth, making the plant more vulnerable to herbicides. Plants can be sprayed with 2,4-D in autumn (September) and burned the following spring (April). This should be followed by another 2,4-D treatment in June and a fall burn in October. The process may have to be repeated many times.
Biological control is being actively researched at many locations and since the 1960s several insects have been released in certain location, most notably the spurge hawk moth, Hyles euphorbiae. Biocontrol agents alone have not so far been effective in controlling spurge populations, but may become valuable if several different insects can be successfully used together or in conjunction with other control methods.
Grazing by goats has been used to control the spread of leafy spurge in pastureland, but the plant will probably resume its spread as soon as the grazers are removed. Cattle avoid grazing this plant.
Failed or Ineffective Practices
Mowing or hand cutting is not completely effective because the root system remains undamaged and new sprouts will reappear rapidly. Also, mowing would have to be done continuously because it stimulates development of inflorescences on the lateral branches. Hand-pulling, digging or tilling is not completely effective because the entire root system must be excavated for complete control of leafy spurge. Pulling and digging can rip or cut the root into smaller pieces, leaving portions to re-sprout. This method could actually increase the number of plants.
Prescribed burning will not be likely to provide adequate control if used alone because its effect would be only on top growth and seeds. Established plants would quickly re-sprout.