What Are Noxious Weeds?

Generally, the term “noxious” weed is used to describe any plant that is non-native, unwanted and grows or spreads aggressively.  Some are poisonous to humans and livestock and most will crowd out desirable and native vegetation.  They can reduce crop yields, damage and destroy recreational opportunities, clog waterways and diminish land values. 

Native plants evolved over millions of years to fill unique ecological niches. What we know as weeds today (non-native, ecologically damaging plants) did not exist in the wilderness then. These plants developed in and are native to other countries. Like our native plants, they are kept in check in their native environment by insects or diseases and by competition with other species.

Early European settlers inadvertently brought weed seeds with them, perhaps in the hay they brought for their animals or in the dirt they used as ballast for their ships or even in their clothes or bedding. Some activities, such as clearing the land, opened up niches that created places for weeds to grow. Settlers also purposely brought plants from their “home country” to reseed areas, make dyes for clothing and use as ornamental plants.

These plants have spread at an alarming rate because, unlike native species, there are no native insects, fungi or diseases to control their growth and spread in this country. What began as a handful of plants introduced in the 19th century now number in the hundreds of millions.  Noxious weeds destroy wildlife habitat and forage, increase erosion and prevent recreational activities.

Weeds have invaded approximately 17 million acres of public rangelands in the West – more than quadrupling their range from 1985 to 1995.  Non-native invasive weeds across the US cost an estimated $26.4 billion per year in agricultural losses.  Approximately 420,000 acres of grassland and national forests in the Pacific Northwest are reported to have been degraded by invasive weeds.  Noxious weeds are a leading contributing cause of native species endangerment.