| Eurasian watermilfoil Myriophyllum spicatum |
||
|
Description |
|
| Growth Habit:
Because it is widely distributed and difficult to control, milfoil is considered to be the most problematic plant in Washington. The introduction of milfoil can drastically alter a waterbody's ecology. Milfoil forms very dense mats of vegetation on the surface of the water. These mats interfere with recreational activities such as swimming, fishing, water skiing, and boating. In eastern Washington milfoil interferes with power generation and irrigation by clogging water intakes.
The sheer mass of plants can cause flooding and the stagnant mats can create good habitat for mosquitoes. Milfoil mats can rob oxygen from the water by preventing the wind from mixing the oxygenated surface waters to deeper water. The dense mats of vegetation can also increase the sedimentation rate by trapping sediments. Milfoil also starts spring growth sooner than native aquatic plants and can shade out these beneficial plants. When milfoil invades new territory, typically the species diversity of aquatic plants declines. While some species of waterfowl will eat milfoil, it is not considered to be a good food source. Milfoil reproduces extremely rapidly and can infest an entire lake within two years of introduction to the system. Although milfoil produces many seeds, we do not believe that these seeds are important for milfoil reproduction in Washington waters. However, milfoil is able to reproduce very successfully and rapidly through the formation of plant fragments. In the late summer and fall the plants become brittle and naturally break apart. These fragments will float to other areas, sink, and start new plants. Milfoil will also grow from fragments created by boaters or other disturbances during any time of year. A new plant can start from a tiny piece of a milfoil plant. This is why milfoil can so easily be transported from lake to lake on boat trailers or fishing gear. Once established in its new home, water currents may carry milfoil fragments and start new colonies within the same waterbody. Habitat: Eurasian watermilfoil is an extremely adaptable plant, able to tolerate and even thrive in a variety of environmental conditions. It grows in still to flowing waters, can tolerate salinities of up to 15 parts per thousand (half the salinity of Puget Sound), grows rooted in water depths from 1 to 10 meters (regularly reaching the surface while growing in water 3 to 5 meters deep), and can survive under ice. It is able to tolerate pHs from 5.4-11. Relative to other submersed plants, Eurasian watermilfoil requires high light, has a high photosynthetic rate, and can grow over a broad temperature range. Eurasian watermilfoil grows best on fine-textured, inorganic sediments and relatively poorly on highly organic sediments. Over the spectrum of infertile to enriched aquatic systems, Eurasian watermilfoil appears to prefer an approximate mid-point, although it occurs in ultra-oligotrophic lakes like Lake Chelan, Washington and hyper-eutrophic lakes like Carlisle Lake, Lewis County, Washington. Growth and Development: Eurasian watermilfoil exhibits an annual pattern of growth. In the spring, shoots begin to grow rapidly as water temperatures approach 15 degrees centigrade. When they near the surface, shoots branch profusely, forming a dense canopy. The leaves below 1 meter senesce in response to self-shading. Typically, plants flower upon reaching the surface (usually in mid to late July). After flowering, plant biomass declines as the result of the fragmentation of stems. Where flowering occurs early, plant biomass may increase again later in the growing season and a second flowering may occur. During fall, plants die back to the root crowns, which sprout again in the spring. In some areas, like western Washington, Eurasian watermilfoil frequently overwinters in an evergreen form and may maintain considerable winter biomass. Eurasian watermilfoil plants do not form specialized overwintering structures such as turions. Carbohydrate storage occurs throughout overwintering shoots and roots.
| ||
