Purple Loosestrife
Photo courtesy SRC Communications
|
|
|
Purple Loosestrife |
Are You Aware of Purple Loosestrife?
adapted from the WATER HAULER'S BULLETIN 1992
Purple Loosestrife or Lythrum saliciaria has become a serious weed pest in several regions of Canada and the United States. The weed causes severe problems in wetlands, drainage ditches, canals, wet meadows, stream and river margins, and lowlands.
Purple Loosestrife is a perennial flowering plant that can grow up to 1.5 metres tall. It has squarish stems, lance shaped leaves that are 3 to 10 em long, and Purple to Purple pink flowers that form a10 to 40 cm long spike. The brilliant flowers which are present from July to September, allow Purple Loosestrife to be recognized from long distances away. A single plant can produce up to 30 or more stems, giving it a bushy appearance.
Purple Loosestrife grows well where there is an abundance of moisture -- areas such as marshes, wetlands, ditches, strearnbanks, stormwater retention ponds, canals, etc. The problem with Purple Loosestrife is that it displaces almost all other native vegetation. It is a strong competitor, it is not eaten or used by most wildlife, and it is highly reproductive.
"The result is that once established in an area, Purple Loosestrife can eventually become the dominant if not the sole type of plant present. Wet areas dominated by Purple Loosestrife cannot be easily used by either man or wildlife. Ditches and canals can become choked by encroaching Purple Loosestrife, preventing drainage or conveyance of water to downstream users. Purple Loosestrife is a concern to wetland managers, irrigation and drainage system managers, naturalists, hunters and fishermen, park managers and people who enjoy nature", says Robert Burland, Biologist with the Pesticide Management Branch of Alberta Environment.
Germination of Purple Loosestrife seeds begins in late spring as the soil warms up. The plant undertakes rapid growth (up to 1 cm per day) until flowering occurs. In fall, the above-ground portion of the plant dies, however the rootstalk remains viable. The rootstalk produces buds during the next spring from which new stems will arise.
Seeds are the prime means of Purple Loosestrife's propagation. It is a, very prolific seed producer Each stem of a single plant can produce upwards of 90,000 seeds.
The seeds can be carried in the water, or can be disseminated by wind, waterfowl or other wildlife. All a seed needs to begin germination is to come into contact with wet soils.
Purple Loosestrife can spread locally by vegetative fragments. Plants that are cut down by wildlife or disrupted by other environmental factors, can float to a suitable location, produce roots and grow.
"Almost every conceivable approach has been tried in efforts to bring the growth of Purple Loosestrife under control, says Burland. No single method by itself has proven to be a solution to the problem."
Subjecting the plant to flooding or desiccation by altering water depth, is not effective in preventing the plant from becoming established.
Cutting the plant may temporarily relieve problems with drainage and water delivery and will delay seed production, however it does nothing to prevent further growth of the plant. Cutting may actually cause an infestation to spread by releasing viable plant fragments into the water where they can begin to produce new plants.
Hand-pulling has basically the same results as cutting unless all of the root matter is removed with the plant. Getting the root mass out by pulling is very difficult unless the plant is in the seedling stage.
|
|
A Saskatchewan dugout surrounded by Purple Loosestrife |
Digging the plant out, along with its roots, is the best approach when dealing with only a few plants. One must be certain that disturbance to the site is minimal, otherwise new weed species will quickly invade. Close monitoring is required.
Herbicide use is restricted at this time as no products are approved for use when the plants are growing in water. Approvals are underway for effective and environmentally safe herbicide use in aquatic situations.
Purple Loosestrife growing on dry shoreline areas or in dry drainage ditches can be treated successfully with certain herbicides, however special approvals from government environmental departments are required before this can be done.
Experiments are being conducted to determine successful insect species that will feed on and effectively control Purple Loosestrife (biological control). These insects, which originate in the plant's native land, need to be carefully screened to ensure that they will not cause damage to native or ornamental plants, however they provide hope for a successful long-term solution to the problem.
"We, in Alberta, are lucky so far, says Burland. Although Purple Loosestrife is present in some areas of the province, its level of infestation is still comparatively low and there is still an opportunity to bring it under control. This is not the case in Ontario where at least 2,000 hectares of wetlands, meadows and ditches are infested. The same situation exists in Manitoba and Saskatchewan where over 500 hectares in each province have been infested," he states.
Purple Loosestrife has recently been added to the Alberta Weed Control Act as a Noxious Weed. This means that a weed inspector may issue a notice to a landowner or lessee, to take measures to control it.
If Purple Loosestrife is found in any wetland area, stream, ditch, or other water body, its occurrence should be reported immediately to the local agricultural fieldman or to Ducks Unlimited Canada. The reporting of sightings is important, as this will allow the location to be documented and monitored. It may also provide clues as to the location of other new infestations, he concludes.
For additional information on Purple Loosestrife or to obtain an information pamphlet, call Toll Free 1-800-565-6305.
