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What is a Noxious Plant?
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Noxious and Nuisance Plant Management Information System

Many noxious terrestrial and aquatic plants cause serious problems across the country. Problem plants include the terrestrial species snakeweed, knapweed, leafy spurge, various thistles, seepwillow, silver leaf nightshade, tansy ragwort, etc., and the aquatic plants waterhyacinth, waterlettuce, hydrilla, Eurasian watermilfoil, and water chestnut, among others.

Problems arise mainly because of the growth characteristics of these plants, which enable them to reach very large population levels relatively rapidly, thereby displacing and subsequently eliminating native vegetation. This in turn causes significant impacts to native wildlife including the elimination of endangered species, disruption of delicate ecosystems by the replacement of native vegetation, decreases in land use and value, reduction of recreational uses, hindrance of navigation along waterways, increased water loss, as well as increases in human health hazards associated with expanding mosquito breeding habitats. Traditional control procedures mainly involve the use of chemical applications, but these offer at best only short-term solutions, and their use is becoming increasingly more environmentally sensitive.

There are now more environmentally acceptable techniques and integrated procedures for noxious plant control. These techniques involve the use of biological control agents and offer environmentally acceptable and, in many cases, long-term answers for weed management. The use of biological control gained public acceptance as early as 1902 with the release of flower- and fruit-feeding insects for the control of Lantana camara. These insects successfully controlled the invasion of lantana in many areas of Hawaii. Since that time over 190 insects have been released to manage 86 weed species with over half of these attempts considered successful. The use of biocontrol for weed management has not been confined to only the terrestrial environment. Many successes have been achieved in the aquatic habitat. These have included the release of 12 insect species to control 4 problem aquatic plants since the beginning of the aquatic plant biocontrol program in 1959. Biological control is rapidly becoming recognized as an important and viable alternative management strategy for weed control. Since 1987, over 40 insect species have been introduced in the United States for the control of more than 15 weed species.

Because of the expanding number and complexity of available plant management techniques, it is becoming increasingly more difficult to obtain pertinent and current information on their use. This is especially true for biological control technology, where a varied assemblage of both introduced and native agents are available for use on selected plant species. Effective use of biocontrol also requires an in-depth knowledge of the agents, life histories, collection techniques, and potential impact, as well as a working knowledge of basic population biology and ecological principles.