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Spread, Impact, and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands

Research and Information Needs

The recent spread of purple loosestrife into Nebraska and Wyoming (Thompson and Yates 1985) completes a cross-continent distribution, and demonstrates that this weed is a problem of national importance. Since dollars for research and control depend on solid evaluations of economic loss, one of the first needs is for studies that demonstrate and quantify actual losses incurred with infestations of L. salicaria in natural and agricultural habitats. Meanwhile, the spread and expansion of the weed's geographic range should continue to be monitored. Best et al. (1981) demonstrated that 10 species of hydrophytes (4 of them L. salicaria associates) can be identified with remotely sensed imagery. This and other inventory techniques should be applied to purple loosestrife. We also need to know much more about the growth, reproduction, and survival of purple loosestrife in relation to its plant associates so that wetland managers can better work within the constraints imposed by the invasion of this weed. Although special formulations for glyphosate and other wide-spectrum agricultural herbicides have been approved for wetland and aquatic use, we know little about the impact of these chemicals on wetland and aquatic plant communities. We also need to test various infertile cultivars of purple loosestrife to verify that these horticultural clones remain sterile under a wide range of sites and conditions. Last, we should continue work on the search for biological control agents in Europe. An interagency biological control program is potentially the most cost-effective and least environmentally damaging control tactic that can be devised.

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