Aquatic weeds in farm dams
Rising temperatures and falling water levels over summer lead to a spate of enquiries concerning control of aquatic weeds in farm dams.
Although farmers are often concerned about whether the weed is declared or is a potential problem, most water weeds sent for identification are native plants that present few problems.
Most commonly found species belong to the pond weed family: Potamogetonaceae. Of these, floating pond weed (Potamogeton tricarinatus), and blunt pond weed (Potamogeton ochreatus) are the most common. Duckweed (Lemna spp.), red azolla (Azolla spp.) and common water milfoil (Myriophyllum propinquum) are also widely distributed, but stonewort (Chara spp.), and sea tassel (Ruppia maritima) are also occasionally reported.
Declared aquatic weeds found in WA include water hyacinth (Eichornia crassipes), salvinia (Salvinia molesta), parrot’s feather (Myriophyllum aquaticum), hydrocotyle (Hydrocotyle ranunculoides) and leafy elodea (Egeria densa). These are not common to farm dams.
Aquatic weeds provide food and shelter for bird life, small crustaceans and fish.
Aquatic weeds can be categorised as follows:
- Emergent weeds: weeds that have stems and leaves protruding above the water surface or grow where the watertable is near ground level. Examples of these are cumbungi, rushes, sedges, paspalum, water couchgrass, arum lily.
- Free floating: these weeds are not attached to the soil, but they may have root systems. Examples are salvinia, water lettuce and water hyacinth (in deep water).
- Floating leaf: these water weeds are rooted to the soil but have long stems that stretch to the water surface and floating leaves. Examples are water lilies, nardoo and hydrocotyl.
- Submerged: these water weeds are mostly completely submerged in shallow water up to 3-4m depth. They are rooted to the soil. Examples are pond weeds (Potamogeton spp.) and elodea.