Typically pond weed control should be the focus of discussion during April and May. However during the last two weeks, a number of individuals have contacted the office with weed concerns in ponds. Many are reporting that they are having problems that they have never before noticed in their particular pond. While many aquatic weeds can spread on the feathers and webbing of water fowl, boats, and other means, the massive flooding experienced by Owen and Clay counties no doubt had a role in spreading pond weeds and vegetation.
Vegetation in ponds is important and necessary for a well balanced pond to main habitat and food chain relationships within the pond. Also key is plant diversity with a large number of different species rather than a large number of a single species of an aquatic plant. Rooted plants can help stabilize banks that also provide shady areas around the perimeter of the pond. One's goal of aquatic weed control should never be to eliminate aquatic vegetation from a pond, rather to manage excessive growth, particularly from aggressive plant species.
Oxygen levels are influenced by plant growth and death which can cause fish kills. Plants produce oxygen during the day during photosynthesis and use oxygen both day and night during respiration. The result is low morning oxygen levels during summer where fish come to the surface for oxygen. When oxygen levels are this low, a fish kill may be imminent.
Even if a fish kill does not occur, fish would be at greater risk to disease and toxicants introduced into their environment. A sudden death of plants in a pond also can rapidly decrease oxygen levels. The plant death results in fewer plants producing oxygen from photosynthesis.
Further compounding the problem is that the decomposing plants respire which uses oxygen that would otherwise be available to fish. While it is difficult to predict plant death from temperature swings, cloudy periods, pond turnover, etc., it is critical that poor pond weed management with improper herbicide timing not be the cause for massive plant death.
What can be done now? Should one do anything now to manage vegetation?
Timing is very important when using chemical weed control methods in the pond. Late spring (April-May) is the best time for most methods of chemical control. Plants are small at this time allowing the herbicide to be more effective. Also the smaller plants help to minimize the mass of the resulting decomposing plants that remove oxygen from the water.
At this point in time, one has a couple of choices. One is wait until spring and focus on issues at that time. The other is to treat small sections, perhaps a quarter or less of the pond area. Duckweed may blow to a particular side of the pond where it could be feasible to treat small areas with diquat. Such treatments may help the pond owner mentally as well as getting some control of the problem started. Cool weather periods and paying attention to oxygen levels which are typically lowest in the early morning may help to guide treatment decisions.
Purdue pub WS-21 Aquatic Plant Management is available online at www.ces.purdue.edu/extmedia/WS/WS_21.pdf with tables suggesting herbicides for various plants.
Also specific to weeds most likely spread by the flood, duckweed and watermeal, check out www.btny.purdue.edu/Pubs/APM/APM-2-W.pdf entitled "Control of Duckweed and Watermeal" on the web.
You can contact the local Purdue Extension Office by calling 829-5020 x14 in Owen County or 448-9041 in Clay County for more information or publication copies regarding this week's column topic or to RSVP for upcoming events. It is always best to call first to assure items are ready when you arrive and to RSVP for programs. While most publications are free, some do have a fee. All times listed are Eastern Time.
July 30 No-till Program w/ Jill Clapperton, Cayuga, 9 a.m.
August 1 No-till Program w/ Jill Clapperton, Vincennes, 9 a.m.
August 6-17 Indiana State Fair
September 13 Nature Daze, Brown County, 9 a.m.