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5. "KNOW THINE ENEMY" - UNDERSTANDING WEED MANAGEMENT THROUGH BIOLOGICAL RESEARCH. James V. Anderson, David G. Davis, Michael E. Foley, and David P. Horvath, Research Chemist, Plant Physiologist, Research Leader, and Plant Physiologist, United States Department of Agriculture-Agricultural Research Service, Plant Science Research, Biosciences Research Laboratory, 1605 Albrecht Boulevard, Fargo, ND 58105-5674 USA.

Abstract. Leafy spurge (Euphorbia esula L.) is an invasive perennial weed which infests greater than 3 million acres of range land in the United States and prairie provinces of Canada. In the U.S., 36 of the 50 states report infestations with the Dakotas, Montana, Nebraska and Wyoming suffering the greatest environmental and economic impact. In the four-state area of the Dakotas, Montana and Wyoming, reports estimate the loss due to leafy spurge infestations of grazing land and wild land to be $129 million annually. Leafy spurge is a major concern to ranchers and environmentalists because left unchecked, leafy spurge can quickly out compete native vegetation in pastures, rangelands, and native habitats. In fact, The Nature Conservancy has termed leafy spurge as "one of the dirty dozen of America’s least wanted invasive species of U.S. ecosystems."

Plants classified as weeds possess 12 or more unique characteristics that collectively impart a weedy growth habit. Several of these characteristics deal with reproductive behavior. Most annual weeds reproduce by seeds; however, perennial weeds like leafy spurge also have the ability to reproduce from vegetative root buds. It is the variable growth and development of reproductive organs (seeds and root buds) that allow weeds to avoid conventional weed control measures. Dormancy is a term used to denote variation in the growth and development of seeds and root buds and is a characteristic of most weeds. Reports have indicated that seeds of leafy spurge can remain in a dormant state for 5 to 8 years; however, most germinate within the first 2 years. Unfortunately, the fundamental basis for dormancy in plants is still poorly understood. To address this problem, the Plant Science Research Staff is currently investigating many facets of dormancy in leafy spurge, wild oats and red rice. To paraphrase the ancient Chinese philosopher Sun Tzu - "know thine enemy and victory will be forthcoming." The impact of understanding dormancy in weeds, as well as the physiology, biochemistry, and genetics of weeds, will improve our knowledge and help us to develop new and useful strategies for weed management.

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