The Five Most Dangerous Plants in America

Invasive species are invading the news. Asian carp are killing off both native fish and the fishing industry in the Great Lakes. Also, a new report links Asian kudzu to air pollution, making the fast-spreading plant an even greater threat than was previously understood. Kudzu tops our list of the newly growing threats from invasive plant species in North America. You could be unwittingly planting these nasties around your house, or simply letting grow as weeds.

Asian Kudzu
The iconic plant was initially welcomed in the United States. Its deep root system was considered beneficial for erosion control. However, the same roots release nitric oxide from the soil at increasing rates. Not only does the chemical damage human lungs, it also blocks the absorption of carbon dioxide among plants that haven't already been crowded out by the kudzu.

Purple Loosestrife
This flowering plant was imported from Europe and Asia as a pretty ornamental, and as a nectar plant for bees. It is now an increasingly costly invader throughout the U.S. It flowers from July to October, quickly spreading seeds and creating large, dense mats that choke out native plants and ruin amphibian habitats.

Several states ban the plant's importation, and an estimated $45 million was spent last year fighting off the "purple plague," as it is now known. Home gardeners can sometimes pull up small patches of purple loosestrife and kill them with herbicides, but larger populations are very difficult to kill.

Japanese Dodder
Another Asian import, this was the only new plant species added to Oregon's 100 most dangerous invaders list. It is a unique-looking gold vine with thick, spaghetti-like stems. Despite a national ban on the sale and transport of Japanese dodder, the vine is widely found in Asian-American neighborhoods, where it is still intentionally planted and used for medicinal purposes. It is a deadly poison, not a medicine, for its host plants, and spreads quickly.

Barb Goatgrass
This ugly weed is also a relatively new invader on the West Coast. It has a higher invasion lever and lower control level than any other plant on the 2010 California Invasive Species List. It also was intentionally introduced as an agricultural crop, but it has since widely invaded rangelands and grasslands. Livestock won't eat the weed, and its namesake barbs can lodge dangerously in animals' eyes and mouths.

Though a small, thriving backyard garden is unlikely to harbor barb goatgrass, it may be spreading in larger properties adjacent to rangelands and grasslands.

Salvinia
This South American invader was first discovered in the Texas 12 years ago, but quickly became a major threat to entire ecosystems. State officials call the ornamental floating fern one of the most dangerous plants in state history, threatening to all but starve the life out of lakes throughout Texas and neighboring states. The most important way to stop the spread of Salvinia is to wash boats and watercraft between uses and between different bodies of water.

Click here for more information about invasive plant and animal species in North America.

Posted by: Steve Graham

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