A successful weed control program depends on the resources available, the weeds present and the ability to carry out effective control methods. The decision-making process, with regard to managing aquatic weeds, needs to follow a number of steps.
Determining the cause of the problem will allow the selection of the best management techniques to address the problem. Consider a number of other factors. Do you need to get rid of the plant entirely, or only partially?
Some plants may grow prolifically in some seasons but not in others and are therefore only a short-term nuisance. Others may proliferate because of temporary conditions, such as low water levels due to drought, but in normal circumstances are less problematic.
If a weed is covering a dam and preventing stock from watering you may think the weed is the problem, but look at what is causing the weed to grow. Nutrient runoff and lack of shading around the dam may be allowing the weed to expand due to high nutrient levels and sunlight exposure. In this case treat the cause of the problem, by preventing nutrient rich runoff going into the dam – plant appropriate vegetation around the dam.
If aquatic weed growth is depleting oxygen levels in the water and causing fish to die it may be appropriate to treat the weed. However, using control techniques that leave dead and decaying plants in the water can also cause de-oxygenation of the water. Large amounts of decomposing plant material lower the dissolved oxygen levels in the water affecting fish and other aquatic organisms.
Consider the long-term consequences of any control method. Using the wrong method could make the problem worse. To prevent a recurrence of the problem, you need to be prepared to manage the water body and its surrounds well into the future. It is also best to use a unified approach when managing aquatic weeds. Individual control methods used in isolation rarely provide adequate long-term control.
Unified management combines two or more techniques in a unified program. A unified program usually provides more efficient and stable control in the long term with fewer undesirable side effects. The advantage of unified management is that it maximises the benefits of the methods and minimises their limitations.
Following is a step-by-step example of unified control of weeds in a small dam.
Mechanically or physically remove plants when they first appear.
If practical, take advantage of dry periods by dredging the dam to deepen it. Deeper water discourages growth of plants rooted in the bottom by limiting sunlight penetration.
Divert nutrient run off away from the dam as nutrient rich waters encourage aquatic weed growth.
Plant trees to shade the dam and therefore, as with dredging, reduce available light to the plant.
Use biological control agents if they are available and are suitable to the particular situation.
Strategic placement of barriers or booms to contain the weeds and to prevent them from spreading can be highly effective.
Continual monitoring of the site is necessary.
Article: AquaticHome5 (permalink) Date: 28 January 2013; 10:39:19 AM AEDT