WINTER DRAWDOWN & HYDRILLA

by Miss Libby

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Posted on Tue Jan 24 2023

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An excerpt from “Winter Drawdowns for Aquatic Weed Control” from a specialist at the Department of Aquaculture and Fisheries, University of Arkansas at Pine Bluff.

 

“The length of sediment exposure and the number of days temperatures are below freezing determine the likelihood of rhizome, tuber and turion death. Longer, drier and colder periods of exposure will have a greater impact. In addition, frost heaving of the bottom sediments can uproot weeds and aid in their destruction. Ideally, the sediments should be exposed for at least 6-8 weeks, with temperatures below freezing (0°C/ 32°F) for two weeks or more.

 

The severity of the winter weather can affect the results of a winter drawdown. A mild winter, especially one with persistent precipitation, may not provide the freezing and/or drying required for plant destruction. Conversely, a cold winter with lots of snow might also lead to disappointing results. Snow is an excellent insulator, so exposed bottom sediments that are constantly covered by snow may not experience the low temperatures required to kill overwintering structures. High levels of groundwater seepage may also reduce or negate the destructive effects on target species by keeping the area moist and unfrozen. In addition, some tubers and/ or turions are buried deeply in the bottom sediment, reducing exposure. For example, hydrilla tubers can often be found almost 10 inches below the surface."

 

A chart in this research article of aquatic plants (page 5) from the Department of Environmental Protection and Department of Conservation and Recreation, EOEA Commonwealth of Massachusetts, shows that hydrilla actually increases in a winter drawdown.

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