Global Agriculture

WSSA Cautions Against Poor Choices That Can Spread Invasive Weeds

26 January 2021, Colorado: Last year many people across the U.S. and Canada received unsolicited packets of seed believed to originate in China. Scientists with the Weed Science Society of America (WSSA) were among those to raise the alarm and say the seeds shouldn’t be planted. Authorities had discovered some packets contained noxious weed seeds that could threaten both agricultural and natural areas.

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Jacob Barney, Ph.D., an associate professor at Virginia Tech who specializes in invasive plants, says the caution is well warranted.

“The decisions each of us make can have long-lasting results that impact future generations,” he says. “When we intentionally or unintentionally plant species that originate outside the region where we live, we run the risk of introducing weedy invaders that can harm our environment, our economy and even human health.”

In fact, some of North America’s most troublesome invasive weeds owe their origins to poor decisions, inattention or a lack of understanding of the potential risks that non-native plants can represent. Even public organizations haven’t been immune – embarking on ill-informed planting initiatives that have triggered new invasions.

Here are a few examples of the many ways new invaders can become established:

Bradford pear trees are a variant of the callery pear, a species that originated in China. They were introduced to the U.S. in the 1960s through the horticultural industry, and millions were planted. Unfortunately, they’ve proved to be a real pest when growing outside their native environment. The trees can crowd out native species and create dense thickets that are virtually impassable. Many cities and states are fighting back by banning the trees and by offering bounties or buy-back incentives to residents who cut them down.

Japanese knotweed was introduced to North America in the late 1860s when a nursery owner in New York received a specimen as a gift from his brother working in Japan. Once planted and shared, knotweed went on to become an aggressive invader that has spread widely across the U.S. It has roots strong enough to grow through foundations, roads, walls and other structures, and it is also hard to eliminate. The New York City Parks Department, for example, has spent more than $1 million over the past decade battling knotweed on city property, but says it is still “out of control.”

Cheatgrass, also known as downy brome in the eastern U.S., is believed to have been introduced to the United States from Europe in the 1800s via contaminated grain and packing materials made from its dense thatch. It then traveled across the country by railway as a contaminant in grain, straw and manure. At one point it was even purposefully planted by the U.S. Department of Agriculture to remediate degraded rangelands. Today cheatgrass infests every region of the U.S. It overtakes native plant species and wildlife habitats, and it is a common pest in crop fields, nurseries and orchards. It also contributes to the spread of wildfires by creating an abundant fuel source that wouldn’t be present in a native sage brush habitat.

Hydrilla made its way to the U.S. a half century ago when a Missouri tropical fish dealer imported the plant from Sri Lanka for use in aquariums. It is now one of the most aggressive aquatic weeds in the South. A separate biotype introduced in the 1980s has now spread across the Mid-Atlantic and Northeast. Today hydrilla is among the most widespread of the 112 weeds on the Federal Noxious Weed list. It can form dense mats of vegetation that grow rapidly and quickly take over a body of water. Hydrilla is known to clog waterways, displace native vegetation, promote fish kills by depleting oxygen, and contribute to harmful algal blooms by disrupting waterflow. It also negatively impacts tourism.

Think Before You Act

To protect against new invasive species and to avoid spreading those that are already entrenched, it is important to think before you act. Here are six tips to help.

Don’t bring it back. You may fall in love with the exotic plants you spot during a cruise or a tour of a foreign country. But take photos and resist the temptation to bring specimens home with you. Federal regulations place strict limits on ANY non-native plant or plant parts you hope to grow back at home. You’ll need a special certification that the plant is safe for import.

Go native. Select plant species native to the region where you live. Unlike non-native plants, you will find they are well behaved and won’t crowd out other beneficial native species. They also provide food and habitat for native butterflies, insects, birds and other animals. Have questions about which plants are native to your region? Consult the resources below:

The Native Plant Society serving your province, state, city or region

U.S. Forest Service List of Native Plant Alternatives

Native Plant Finder, recommended by the National Wildlife Federation

Audubon Society Native Plants Database

Cooperative Extension Service specialists affiliated with the land grant university in your area

Make smart purchases. If you are planting from seed, buy local seeds certified to contain minimal contaminants. Read the label carefully to see what’s included so you don’t plant non-native invaders that can overrun your garden.

Be careful outdoors. Take commonsense measures to make certain you aren’t transporting invasive weeds as you travel and enjoy camping, boating, hiking or other outdoor activities. Carefully inspect and wash your boat, vehicle, ATV, hiking boots or other equipment to remove any plant fragments or seeds you’ve picked up along the way. And avoid carrying firewood with you from one location to another. For additional tips, visit:

Play Clean Go

Stop Aquatic Hitchhikers

Become a “spotter.” Early detection of new invasive weed outbreaks can help authorities take swift action to prevent further spread. Familiarize yourself with the invasive weeds most prevalent in your area – information that is available through the Invasive Plant Council covering your state or region.
These same organizations typically have reporting protocols for new infestations you might discover. If you snap a photo, the GPS coordinates on your phone can help authorities locate and eliminate the invaders you find. EDDMapS can be used across the U.S. to report these weeds from the web or your phone.Another useful resource is Wild Spotter, a program devoted to engaging and empowering the public to help find, map and prevent invasive species in America’s wilderness areas, wild rivers and other natural areas. WSSA and its regional affiliates are partners in the initiative.

Stay informed. Take advantage of webinars and information resources available during National Invasive Species Awareness Week (NISAW), scheduled for February 22-26, and May 15-22, 2021.