A NATURAL FOCUS with Laurie Sanders

PURPLE LOOSESTRIFE

Many of the plants in our yards, along roadside edges and pushing up through the cracks in the sidewalk aren’t native to North America, to other parts of the world, especially Europe and Asia. Hello, I'm Laurie Sanders. During the last few centuries, thousands of plants and animals have been transported to the US. Some, like many of our crop and ornamental plants, were brought intentionally, others were complete accidents and came buried as seeds in ship ballast, stuck to animal fur or often mixed with other imported materials. The result: of the 2700 plants growing wild in our area, nearly 30% are non-native; that’s roughly 900 species.

Most of these aren’t a problem; the familiar wildflowers, like black-eyed susans, Queen Anne’s Lace, and hawkweed, grow only in the open borders along our roadsides and yards. But, then there is a special subset. A small group of plants that invade, not just altered areas, but natural plant communities too. Under the right conditions, these silent invaders can outcompete native plants and drastically alter habitat conditions. Often referred to as aliens or exotics, these aggressive plants have botanists, ecologists and preserve managers scrambling to come up with techniques to control their spread. To give you a sense of the extent of the problem, nationwide about 3 million acres are altered by invasive plants every year and approximately 60% of the habitats of our endangered species are threatened by aggressive non-native plants.

Of the 900 or so non-native plants in our New England landscape, only a few dozen qualify as serious pests in our forests, wetlands and other natural areas. Of these, the most widely known is purple loosestrife. Most people notice it in July and August when its spectacular magenta spires carpet many of our wetlands and line the drainage ditches along almost every major highway in the northeastern US. A native of Eurasia, purple loosestrife arrived in northeastern North America in the early 1800's. It’s introduction was probably both deliberate and accidental. From a few points of entry, purple loosestrife spread throughout temperate North America; it is presently found in 48 states and into southern Canada. But within this wider range, it’s most troublesome in the northeast, great lakes states and mid-Atlantic region.

Purple loosestrife exhibits all the traits of a model invasive: First off, it can live in a wide range of conditions: Although it doesn’t spread to upland areas, it grows in a variety of wetlands-- in freshwater marshes, along river banks, in floodplains, wet meadows, pond edges, and in roadside ditches. Although it does best open sun, it readily survives in partial shade. It can live in acid soils and basic soils.
Secondly, it matures quickly and lives for years. What's more, its a prolific seed producer. Each stalk can produce more than 2500 flowers and each rootstock can send up 30-50 stalks a season. The flowers attract a wide range of pollinators, and by the end of the summer, a single plant can yield more than two million seeds. The seeds can disperse long distances, via wind, water, on the feet of marsh animals, or the tires of heavy equipment. On top of this, it also spreads underground by its roots.

In spite of its beauty, these extensive, permanent stands outcompete native plants for sunlight, water and nutrients. And although attractive to bees and butterflies, when it replaces a mix of cattails, rushes, grasses and sedges, it reduces the wetland’s value for food, shelter and nesting sites for most birds, muskrats and other mammals. And rare plants wouldn't have much of a chance trying to grow in an aggressive single-species stand like this?

Like many non-natives plants and animals, purple loosestrife arrived free of diseases, parasites and predators. In Europe, insects and disease keep the populations low, generally under 200 plants in a single marsh. In contrast, some of our marshes contain over 2 million plants! Because none of our native insects eat enough purple loosestrife to suppress it, until recently the most common techniques for controlling it were hand-pulling, repeated cutting or spot treatments of herbicide. All these methods are very labor and time intensive and costly. At present, loosestrife control in the US amounts to about 1 million dollars/year. But ecologists have pinned their hopes on new biological controls; specifically 2 types of leaf-eating beetles and a root-mining weevil. Ironically the insects are themselves non-native. They are native to Europe, where they feed on purple loosestrife. After monitoring them in the laboratory and exposing them to 50 types of native plants, botanists are convinced that these insects will eat purple loosestrife and only purple loosestrife. Donna Ellis of UCONN’s Plant Science Department, working in cooperation with Cornell University, has released beetles in several of CT's infested wetlands.
And so far the results are impressive. Where beetles were release last year, their offspring have munched the leaves and dramatically reduced the loosestrife’s size and flowering capacity. At this rate, botanists predict that the three insect species will reduce these dense stands by as much as 90%; within 5 years, some smaller marshes may be largely free of purple loosestrife. But it won’t be gone entirely. The insects will reduce the populations to manageable levels. Rather than the solid stands we have now, purple loosestrife will be just one of the many plants that grow in our diverse wetlands.

Questions and Activities after Watching the Video

1. Do you have any wetlands in your community that have been invaded by purple loosestrife? Use a topographic map to plot their locations and size.

2. Collect a specimen and put it in a plant press. Take some photos of the wetland it came from and prepare an educational poster about this troublesome wetland invader.

3. Do some data collection on the types of insects that are attracted to purple loosestrife. This is a good way to learn how to identify some of our butterflies.

4. Contact your local conservation commission to see if there are any rare wetland habitats that can be monitored for purple loosestrife. Set up a work crew to hand-pull (getting the roots out too!) if an invasion is just starting.

5. Make a display of common non-problematic, non-native plants vs. some that are troublesome invaders.