By Joel M. Lerner
Saturday, October 11, 2008
Here's the test: How do you feel when you see a large slope planted with English ivy?
If you gasp in horror, you're in the vanguard of the native-plant movement. If you think, "How pretty," you might be aesthetically correct. But, from a practical standpoint, you may want to reconsider.
The plants and animals that naturally exist in a place evolved together, adapted together and coexist for mutual benefit. Birds, insects and other animals help pollinate plants and distribute seeds. Plants provide food and shelter for the animals.
When you start adding exotic or nonnative species, or subtracting native species, you disrupt the balance. Native creatures may not be able to get nourishment from nonnative plants, and indigenous plants may not be able to compete with invasive alien plants.
Another problem with nonnative plants is that some of them can escape. Even a well-tended garden can naturalize into the wild with the help of birds, bees, wind and a vigorous growth habit, driving out native species.
Norway maples ( Acer platanoides) are a prime example. The leaf looks like that of a sugar maple but without the magnificent fall leaf color and sugary sap. They are prolific seeders. One Norway maple can eventually colonize many areas of otherwise native woodland. The mixed, deciduous woodlands typical of the mid-Atlantic could give way to stands entirely of Norway maples, if we don't manage the woods and give time for slower-growing seedlings to dominate, such as oaks and hickories.
Russian olive trees, once used to control erosion, are highly invasive and damage habitat for wildlife. Purple loosestrife ( Lythrum salicaria and Lythrum virgatum) are garden plants that have escaped to colonize millions of acres of wetlands.
Faced with a 60-foot-long slope of English ivy, or a big Norway maple on your property, what should you do?
The simple answer is, rip it out, according to the Maryland Native Plant Society. "If you cannot effectively contain these plants within your property, by clipping seeds, fruits, or runners, consider removing them," according to guidelines on the society's Web site, http://www.mdflora.org/publications/invasives.htm.
Replace invasive plants with native shade trees such as white oak ( Quercus alba), red oak ( Q. rubra), Southern red oak ( Q. falcata) and mockernut hickory ( Carya tomentosa). Instead of English ivy, the native plant society recommends American bittersweet ( Celastrus scandens) or trumpet honeysuckle ( Lonicera sempervirens).
So, how do you get rid of these unwanted plants? The Maryland Native Plant Society offers the following suggestions.
In the case of Norway maples, there are a number of methods: pulling seedlings and digging out larger plants; cutting down the tree and grinding out the stump; clipping off sprouts and girdling the tree (cutting through the bark and the growing layer all the way around the trunk about six inches from the ground), which is most effective in the spring; hacking several holes into the growing layer and squirting in glyphosate, which is sold under many names including Roundup, Touchdown Total, Rodeo Herbicide and Glypro. Cut down the tree and paint the stem or stump with glyphosate, or paint the foliage with glyphosate following all labeled directions for a "wiper" method of application. This is most effective in middle to late summer.
Most amateur gardeners are surprised to learn that mature English ivy will flower and go to seed. To control English ivy, clip off any flowers or fruits and pull up seedlings. To eradicate it on trees, cut the stems as far above the ground as you can reach. Then pull them down and paint the lower portion of stems and foliage with a bush and stump killer containing triclopyr, sold under the names Crossbow or Garlon 3A herbicides. Avoid getting any on the tree bark.
To get rid of ivy as a ground cover, pull up as much as you can, dig out the roots as thoroughly as possible and keep doing so until it no longer resprouts -- or treat it with triclopyr, if you must.
Controlling or getting rid of English ivy can be hard work. You might want to consider tackling small areas at a time. Make sure you identify poison ivy as you work. It is a native plant, good for wildlife, but it can be a nasty skin toxin to humans.
Other recommended methods of controlling or ridding your property of invasives include deadheading ornamental plants, mowing, cutting back grassy areas at least three times a season and using a corn-based pre-emergence herbicide (for use in lawns and gardens, not woodlands). Spot-treat difficult plants with a broadleaf weed-killer.
The native plant society strongly recommends physical methods for getting rid of plants, as opposed to using herbicides. But where plant stands are large or hard to control by clipping or pulling, chemicals may well be the last resort.
Glyphosate should not to be used near bodies of water. The runoff is not good for aquatic life. So cutting, pulling, stump grinding and removal of seedlings by hand might be the best methods. Follow labeled instructions for any chemicals.
Biological control is another emerging treatment for management of large populations of undesirable plants. This method is more often used to control undesirable insects.
A report this spring from the Weed Science Society of America, a nonprofit professional group, says weed scientists at the University of Minnesota and the Minnesota Department of Natural Resources released two types of beetles that feed on purple loosestrife, which is listed as one of the top noxious weeds in 33 states. Just one plant can produce 100,000 to 200 million small, lightweight, easily distributed seeds. Two years after the release of the beetles Galerucella calmariensis and Galerucella pusilla, they found significant reduction of loosestrife populations and seed production. Five years later, they found a dramatic reduction in loosestrife stands.
Like the loosestrife, the beetles are imported from Europe. But according to a University of Michigan Web site, these beetles eat only loosestrife, so they're not a danger to native plants. And they're also harmless to humans and pets. When the loosestrife dies down, so does the beetle population.
The program has been so successful since its inception in the early 1990s that it has been adopted in 13 Midwestern and Northeastern states. Beetles have been handed out to agricultural inspectors, transportation department personnel, schoolchildren, and members of 4H and garden clubs to distribute in infested areas.
Minnesota has released an astounding 8 million beetles since the program began, and Nebraska has released about 500,000 per year since 1997 to combat loosestrife along the Niobrara National Scenic River in Nebraska and the Missouri River. A U.S. Army Corps of Engineers park ranger who oversaw the Nebraska effort said that loosestrife populations had been reduced by two-thirds in eight years.
A researcher at the University of Nebraska, Stevan Knezevic, reports that the beetles decimate the loosestrife not only by stunting it but also by delaying the weed's flowering by stripping away its canopy. That reduces the need for herbicides.
According to the Weed Science Society, the research that led to the beetle bio-control program was an international effort involving scientists and managers from the University of Minnesota, the Minnesota Department of Agriculture, the Minnesota Department of Natural Resources, local parklands, Cornell University and CABI Bioscience of Delemont, Switzerland.
As time goes on and awareness grows regarding the destructiveness of invasive, nonnative plants, we hope that more types of biological and other kinds of interventions will be developed. It would be great to find a beetle that likes to chow down on Norway maples.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site,http://www.gardenlerner.com.
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