The largest local duckweed is in fact a type of aquatic fern. It is prominent at this time of the year because it likes sunny days and warm temperatures.
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Not readily recognised as a fern, this plant, known as azolla, breaks into smaller pieces as it grows. In good conditions its area can double in size every week.
Its presence often indicates high nutrient levels, with the plant using nitrogen from both water and air for its growth.
Farm dams and slow moving streams are preferred places for azolla.
It is common at present in some of the channels in Fairyland at Lake Wendouree, where it is used as food by swans, black ducks, grey teal, coots and other waterbirds, although none of them seem to graze it preferentially.
Sometimes we see dams covered with this green “duckweed”, without any open water visible. At times the plants are reddish, with this colour being associated with more sunlight.
Although common and obvious at this time of the year, the forthcoming cooler weather of autumn will decrease its vigour and stifle its growth. It has a low tolerance of frosts.
When it is abundant, azolla can become a nuisance in irrigation channels and drains. Its blanketing effect can result in underwater plants deteriorating through lack of sunlight.
It is not harmful to stock, and its presence – with its fondness of higher-nutrient waters – can potentially reduce the likelihood of blue-green algae outbreaks.
Our azolla has been introduced into other parts of the world. It has become a pest in some places, such as South Africa, where it is a declared noxious weed.
Its scientific name is Azolla filiculoides.
It is sometimes added to ponds because of its attractive appearance and its ability to shade and cool water, thus reducing evaporation. It is easily transported by floodwaters.
Small amounts might be carried from place to place by waterbirds.
FIRE CHASERS
Birds of prey are immediately attracted to smoke – and bird observers chase fires to look for the birds of prey.
Now that the stubble burning season has commenced, there has been an increase in the visiting raptors, which seem to immediately appear from nowhere to search for small wildlife disturbed by the flames and smoke.
At a recent Allendale burn off, one whistling kite, one brown falcon, one black falcon and four nankeen kestrels were seen.
Two more fires provided eight black kites, two distant unidentified falcons and one stubble quail.
