Floating pennywort
Floating pennywort - Hydrocotyle
ranunculoides - is a North American plant
which was introduced to the UK in the 1980s
by the aquatic nursery trade.
Floating pennywort roots in shallow
margins of slow-flowing water bodies,
particularly in ditches, slow flowing dykes and
lakes. Here it forms dense mats of covering the water’s surface and out
competing most native aquatic plants. This
causes deoxygenation of the water, which in
turn affects fish and invertebrate populations
and causes a choking of drainage systems and
sluices, sometimes causing localised flooding.
Floating pennywort is difficult
to control because of rapid growth rate (up to
20 cm a day) combined with the ability to regrow
from a single node.
Control
Mechanical control - Floating pennywort can be cut by weed cutting boats. These techniques will only offer a very short-term reduction in the local extent of the plant, as it is capable of growing back rapidly from single nodes. Re-cutting will be necessary throughout the growth season. However, without thorough removal of all cut material, the plant will spread .
Where cutting is deemed appropriate, the affected areas should be carefully fenced or, netted off, to reduce the risk of downstream infestation and to ensure that all cut plant material can be removed. This is especially important in flowing situations. Mechanical removal can be practised to reduce the biomass for subsequent chemical treatment and to ease access for herbicide application, especially in dense masses.
Chemical control - Due to the dense nature of the vegetation spraying of approved herbicides has limited effect, but a follow up treatment after our Truxor has removed the weed beds would be advisable using approved herbicides.
Although the growth of Floating pennywort is noticeable throughout the season (it may completely cover small slow flowing channels or ditches in the late summer) it does not usually reach nuisance proportions on larger water bodies until later in the summer or early autumn. However, treatment earlier in the season will reduce manhours, equipment and chemicals needed to control the weed at a later date. Agreement must be obtained from the local Environment Agency office before applying herbicides in, on or near controlled waters.
Removal of the dying weed mass by our Truxor should be doen to prevent deoxygenation of the water due to decomposing weed.
Biological control - There are no known methods of biological control appropriate for use in the UK.
Environmental control - There are several methods that may be used, none of which give a complete solution. Shade may be an effective method of control as the plant does not establish well in shaded conditions, and is best achieved by planting trees on the south side of the water body. This is unlikely to be practical to implement on larger water bodies. Increasing flow will restrict the growth of Floating pennywort in situ but may increase the spread of the plant downstream. Increasing rooting depth to below 1 metre may reduce the ability of Floating pennywort to root at the margins. This, however, is unlikely to be a feasible option.