Control and Management
No single method will control leafy
spurge in all the environments in which it is found. The most successful
leafy spurge treatment strategies use a variety of control tools
in an integrated and adaptive manner through time (years).
Chemical Control
Traditionally, herbicides have been used to control leafy spurge and long-term herbicide programs have been relatively successful. Many herbicides have been used to control leafy spurge with varying degrees of success (Lym and Messersmith 1983). These include Picloram, 2,4-D, Dicamba, Glyphosate, and others. At the leafy spurge symposium at Montana State University in 1985 it was shown that Picloram is the most effective in controlling spurge. Because Picloram is expensive, the less costly herbicide 2,4-D is sometimes used alone or mixed with picloram on large areas of spurge infestation. However, herbicide use is not always acceptable due to its high cost, potential for groundwater contamination, and prohibition in environmentally sensitive areas. A recent study has shown that 2,4-D when used as a set-up treatment for Picloram has virtually no effect on control of spurge (Gamal 1986). Biannual application of 2,4-D alone likely only prevents seed production and spread of spurge with little change in area of original infestation (Lym and Messersmith 1987). Messersmith (1987) reported that low rates of picloram with 2,4-D in repeated treatments gave the best long-term control of spurge. Although 2,4-D used alone does not offer as effective control as picloram, it may be preferred in some cases due to its lower cost and perceived lower health risk (Welles pers. comm., MRO, 1987). Dicamba and 2,4-D are often used as follow up treatments to picloram but with mixed and often disappointing results (Bybee 1981, Mitich 1972).
Herbicides have been the primary method used for leafy spurge control and have been effective, especially when applied at recommended rates and the proper time (see NDSU Extension Circular W-765 "Leafy Spurge Identification and Control" for more information). However, herbicides have become cost prohibitive when treating widespread infestations which continue to expand. With present and future concerns over groundwater quality and environmentally sensitive areas, herbicide use may become further restricted, or even eliminated.
Biological Control
Non-chemical methods for control have been developed, including the introduction of multiple biological control agents.
The U.S. Department of Agriculture has
demonstrated leafy spurge control using six natural enemies of leafy spurge imported from Europe. These include:
(CLICK FOR LARGER IMAGES)
- a stem and root - boring beetle (Oberea erythrocephala)
- four root-mining flea beetles (Aphthona spp.)
- shoot-tip gall midge (Spurgia esulae)
Large scale field-rearing and release programs of these approved bio-control agents are carried out cooperatively by Federal, State, and local officials in many infested states. Bio-control treatment effects are not as immediately apparent as herbicides but used on an appropriate site, large numbers of biological control agents build up within a few years and leafy spurge reductions may be impressive.
BEFORE BIOLOGICAL CONTROL / AFTER BIOLOGICAL CONTROL
GRAZING FOR CONTROL
Goats and sheep have long been used for weed control. Their use has increased in recent years because of the need for non chemical treatment options in environmentally sensitive areas. Sheep mostly graze forbs (broad leaf herbaceous plants) while goats generally consume shrubs. Sheep and goats became popular control agents to control leafy spurge in the northern Great Plains region in the mid 1980s and the 1990s. Ironically, sheep were proven to be effective for controlling leafy spurge in the 1930s while goats were first used in the 1980s.
Cattle do not utilize leafy spurge and avoid leafy spurge infested sites.
Sheep and goats can be integrated with chemical and biological control as part of an integrated weed management strategy for control of leafy spurge. In addition, sheep/goat grazing can generate an economic return from land that other livestock won't graze. The land manager can control leafy spurge by grazing sheep or goats and provide a highly nutritional diet for the livestock.
CULTURAL CONTROL
Cultural control of leafy spurge includes properly timed cultivation and/or planting of competitive grass species. Less successful cultural methods also include mowing and prescribed fire. All cultural control methods are more successful when integrated with other weed control methods than when used alone.
Few options for weed control in a growing crop are available. Herbicide rates required for leafy spurge control are greater than rates labeled for use in cropland. A non-chemical control method such as cultivation is desirable to prevent the rapid establishment of leafy spurge in cropland, especially in limited-tillage areas.
Two types of tillage programs generally are used for leafy spurge control, intensive tillage throughout the growing season and fall cultivation. The intensive cultivation program precludes crop production and should begin in the spring, two to four weeks after leafy spurge emerges. Using a duckfoot or similar cultivator infested fields are tilled 4 inches deep. Cultivation should continue every three weeks until the soil freezes in the fall for one to two growing seasons. The tillage schedule should not be interrupted because leafy spurge recovers quickly from the effects of cultivation. Pieces of roots as small as 0.5 inch long and 0.1 inch diameter can produce new shoots. Root pieces also will survive two or three hours of drying in the hot sun.
A second option, fall cultivation, is when the plants are 3 to 6 inches tall post-harvest. Research at NDSU has shown that cultivating leafy spurge twice each fall after harvest for three years provided complete control. The fall cultivation program has an advantage over the season-long program because it allows crops to be grown during the season and limits soil exposure to ero-sion. Two fall cultivations will reduce leafy spurge infestations faster than one cultivation. However, a single cultivation may be a more practical man-agement option when minimal tillage is desired or soil erosion is a concern.
The amount of time needed for leafy spurge control through cultivation can be shortened when combined with herbicide treatments. Apply effective herbicides to leafy spurge at rates labeled for use in the prospective crop at least seven days before the first fall cultivation.
Some perennial grass species can effectively compete with leafy spurge and provide control. The most competitive grasses include wheatgrass, wildrye, and smooth brome. Leafy spurge topgrowth reduction averaged 70 to 80 percent in trials conducted at Fargo and Jamestown . The most competitive species can vary by region, so consult with a local agronomist for the species best adapted in your area.
OTHER CONTROL METHODS
Prescribed Fire would not be likely to provide adequate control of leafy spurge if used alone. Fire effects top growth and seeds, and established plants will quickly resprout. Fire used in conjunction with herbicides may give better control than herbicide application alone (Messersmith pers. comm. 1987, Bjugstad pers. comm., South Dakota School of Mines, 1987, Plumb pers. comm., Ordway Prairie, South Dakota, 1987, Smith 1987). Plumb (1987) suggested that burning in early May followed by herbicide application in June (just before seed set) might offer adequate control.