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Biological Control of Leafy Spurge

The Problem


JPEG - Grazing cattle ignore leafy spurge areas
Cattle tend to ignore stands of leafy spurge because chemicals in the weed irritate their digestive tract.
 
JPEG - Map of affected areas

Leafy spurge stands cause heavy damage in the northern Great Plains. Ranchers need to take precautions to limit further spread.


Leafy spurge (Euphorbia esula L.) has taken over millions of acres of western grazing land. An aggressive, exotic perennial weed, it has greatly reduced the carrying capacity of the range. It readily outcompetes desirable native vegetation. Because of irritating chemicals in the weed, cattle and horses generally don't graze on it, and they even avoid nutritious forage growing nearby. The damage costs ranchers an estimated $35 to $45 million per year.

Herbicides have been used against leafy spurge, but infested acreage is so extensive that chemical control isn't practical. For one thing, herbicides sprayed to kill spurge also kill desirable broad-leaved range plants.

Secondly, chemical control is expensive. A 1984 study by the University of Wyoming put the cost of applying herbicides at $72 per acre. Costs of spraying outweigh the benefits by as much as 10 to 1.

Furthermore, the weed is hard to kill with chemicals. It has a pervasive root system and seems to be able to block the downward movement of herbicides.

To bypass these difficulties, the U.S. Department of Agriculture is coordinating a major biological control program that involves importing and distributing the weed's natural enemies. Biological control specialists in USDA's Animal and Plant Health Inspection Service are concentrating on insects that have evolved to feed only on the target weed, leafy spurge. Collectively, the feeding insects inhibit the weed's growth and reproduction and reduce its ability to compete with desirable range plants.

JPEG - Infestation of leafy spurge
Spurge infestations can be quite attractive to the eye. Only when it comes to economics does the plant take on an ugly cast.


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