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Cornell University : Cornell Cooperative Extension
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| Yates Association |
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Purple Loosestrife |
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In the early to mid-1800's, purple loosestrife was introduced to the United States from Europe. Like many other introduced species, this perennial plant gained a foothold on the continent and has since extended its range to include much of the northeast and portions of the midwest. Purple loosestrife occurs most commonly in moist soil habitats associated with floodplains, marsh edges, stream and river margins, drainage ditches, and seasonally flooded impoundments. Once established, the plant is extremely hardy. Its resistance to changes in soil moisture and temperature and its prolificacy give it a competitive advantage over many of our native moist soil plant species, including cattail. Consequently, many wetlands which once were interspersed with a wide variety of plant species are rapidly being taken over by purple loosestrife. This loss in plant diversity can only be followed by a loss in the numbers and variety of wildlife inhabiting such areas. It is relatively easy to recognize purple loosestrife. The plant grows to an average height of 5 feet and has lance-shaped leaves, 2-4 inches in length which are sessile (without stalks) and occur on opposite sides of squarish stems. In mid - to late summer, numerous upright branches bear long spike-like panicles of rose-purple flowers. These flowers continue to develop and bloom into early fall. Even after bloom, the upright stems and copper colored fruiting capsules are distinctive. Purple loosestrife is very hardy and has proven difficult to control. A variety of control techniques ranging from hand pulling individual plants to flooding large stands with water have been used with varying degrees of success. The most important aspect of a control program is a thorough understanding of the plant's life history. Given proper conditions for germination, the tremendous number of seeds produced from only a few loosestrife stems can lead to rapid encroachment of the plant into a wetland area. When detected early, effective control can be obtained by removing individual plants by hand provided that the root system is completely removed as well. Sections of root left in the ground will sprout and form new plants. If loosestrife is allowed to form solid stands, the option of hand pulling is soon lost. As loosestrife becomes established in an area the chances for successful control rapidly diminish. Mowing or cutting loosestrife, where possible, has been shown to decrease plant vigor and retard seed production. However, this method is generally not effective in offsetting growth from resprouting Loosestrife sprouts that arise after mowing in June or early July are still capable of flowering and producing seed during that same growing season. Mowing in mid-August results in sprouts that will not flower, but the cut stems contain many viable seeds. Unless removed, this seed source will be available the next year. The best results from a single mowing are obtained in mid - to late July when the sprouts are not likely to flower and the cut stems do not contain appreciable numbers of viable seeds. Raising the water level in a marsh or impoundment can be an effective method of retarding the growth of loosestrife seedlings and reducing the vigor of established plants. However, the increase in water depth must be adequate to cover all new plants completely. Shallow flooding will have little effect. As a wetland species, loosestrife has evolved mechanisms for coping with periodic flooding. Within days after being flooded, the plant sends out stem roots and forms a porous, spongy bark layer which facilitates the exchange of gases necessary for growth. Very limited control of loosestrife has been obtained through the use of herbicides. Applications of 2,4-D and Dicamba (trade name: Banvel), two growth regulators commonly used on broad-leaved and woody plants respectively, have been found to be of no greater value than mowing. The use of such chemicals presents the added risk of environmental contamination. The early detection and removal of purple loosestrife from wetland habitats can effectively decrease the plant's rate of proliferation. Complete removal of established populations of loosestrife is unlikely without adversely affecting the native vegetation. Invasion of this exotic perennial has already resulted in the exclusion of native moist soil plant species from many acres of wetlands in the northeast. If left unchecked, the detrimental effects of loosestrife encroachment will continue to place an additional stress on wildlife resources already plagued by the loss of valuable wetland habitat. Cornell
Cooperative Extension Yates Association |
