Parrot’s feather: Water level drawdown
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
This intervention, although limited to waterbodies in which water levels can be regulated, has the potential to reduce or eliminate aquatic invasive plants (Hussner et al. 2017). Water level drawdown consists of reducing the water level of a waterbody to expose submerged plants to drying (or freezing) conditions (De Winton et al. 2013). Desiccation may then result in plant mortality. However, parrot’s feather plants can withstand some level of desiccation (Cook 2004) and therefore control using this technique is dependent on the duration of the water level drawdown. The reduction of water levels could also impact non-target native aquatic species.
Cook C.D.K (2004) Aquatic and wetland plants of Southern Africa. Backhuys Publishers, Leiden.
De Winton M., Jones H., Edwards T., Özkundakci D., Wells R., McBride C., Rowe D., Hamilton D., Clayton J., Champion P. & Hofstra D. (2013) Review of Best Management Practices for Aquatic Vegetation Control in Stormwater Ponds, Wetlands, and Lakes. Auckland Council technical report, TR2013/026.
Hussner A., Stiers I., Verhofstad M.J.J.M., Bakker E.S., Grutters B.M.C., Haury J., van Valkenburg J.L.C.H., Brundu G., Newman J., Clayton J.S. & Anderson L.W.J. (2017) Management and control methods of invasive alien freshwater aquatic plants: A review. Aquatic Botany, 136, 112-137.
Supporting evidence from individual studies
A replicated, randomized, controlled, laboratory study conducted between 2008 and 2009 in the USA (Wersal et al. 2013) found that water removal in order to expose plants to drying during the summer (summer dry outs) reduced survival of parrot’s feather Myriophyllum aquaticum more than water removal during winter (winter dry outs). For four out of five comparisons, the survival of parrot’s feather plants exposed to dry outs of the same duration was lower in summer (0–75%) than in winter (68–80%). After a dry out of 12 weeks, parrot’s feather survival was 18% in summer and 78% in winter. Parrot’s feather shoots were propagated in 3.78 l pots placed inside 1100 l containers filled with water. Four containers, each with 10 pots, were exposed to dry outs of two, four, six, eight and 12 weeks duration, or no dry out, in each season. Winter dry out was initiated in January and summer dry out was initiated in July.Study and other actions tested