Runice posted on October 01, 2011 07:02
At first blush, the rows of lovely purple blooms of the purple loosestrife may seem a desirable addition to our landscape. However, its pleasing appearance conceals a very real threat to our ecosystem. Purple loosestrife, an aggressive perennial plant of European origin, systematically crowds out native wetland vegetation. The plant is widely distributed throughout the United States, is becoming more abundant along the Mississippi River in Minnesota, Wisconsin and Illinois, and ultimately could become the dominant plant.
Purple loosestrife is known for its amazing seed production, producing up to three million seeds per plant, which are small and easily dispersed by wind. Not only are the seeds spread easily, but the plant is extremely hard to remove once it takes hold. The shallow, woody root system forms a dense mat, making adult plants difficult to pull. Moreover, if the entire root is not removed it will resprout. Mowing actually makes it worse because the stem pieces will send out new roots which eventually become anchored and begin new colonies. A final menacing characteristic of the purple loosestrife is that the seeds remain viable for years when submerged and need only a dry season to resprout.
Purple loosestrife has little or no value as habitat or food for wetland animals. Waterfowl avoid wetlands that have become dominated by purple loosestrife. Purple loosestrife overcomes native cattails which are important to nesting waterfowl. In addition, the seed does not provide food for songbirds, nor does the plant provide habitat for muskrats. The loss of waterfowl habitat also decreases the acreage available for hunting.
Unfortunately, the conventional control methods like hand pulling, cutting, flooding, herbicides, and plant competition have not been very effective in controlling purple loosestrife. Biological control (biocontrol), using a living organism to control a pest, has now been introduced as an innovative way to deal with this ecological threat. The Wisconsin DNR coordinates a statewide biocontrol program that was developed after many years of field testing to ensure that there would not be detrimental effects. Illinois also implemented such a program in 1994.
The most successful biocontrols known for purple loosestrife are the Galerucella beetles. The leaf-feeding beetles reduce the growth and reproduction of purple loosestrife by feeding on the leaves of purple loosestrife and laying their eggs on them. Once the eggs have hatched, the larvae feed on the leaves and stems as they move down into the soil. The larvae cause the most damage to the plant and reduce the number of seeds produced. The beetles feed primarily upon purple loosestrife and, although they feed sparingly on a few native species, the risk to these species in releasing the beetle is much lower than it would be if the purple loosestrife were allowed to thrive. Once the loosestrife is controlled, beetles either move on to a new site with loosestrife or die out. In addition, the Galerucella beetles have many predators and are eaten by a variety of birds and insects.
This experiment has been successfully implemented in a number of locations throughout Wisconsin and Illinois since 1994, including many hydroelectric dam projects in Wisconsin. The results are still being monitored, but they are very promising with up to a 90% reduction in purple loosestrife seen in some instances. The goal is not to eradicate purple loosestrife, since that would be almost impossible but to decrease the number of plants, the size of the plants, and the vigor and seed production of the plants. Monitoring shows that the beetles have been successful in doing this, thus increasing the diversity of the native species. This amazing innovation has allowed native plants to flourish once again.
