Pond Bacteria and Herbicides

One question often asked about using pond bacteria in a weed infested pond is: “What effect do aquatic herbicides have on pond bacteria?”  The interaction is important to consider when one’s pond is subjected to obnoxious submerged weed growth.

The primary thing one should consider is keeping the bacterial population at a healthy, high level.  Adding bacteria to a pond at least once a month will help to keep that level at an optimum level.  Natural Pond Cleaner is a great source of friendly pond bacteria.

Now, what kind of an effect do herbicides/pond-algaecide have on pond bacteria?  Research has indicated that copper sulfate can have a destructive effect on pond bacteria.  It has long been known that copper sulfate is an excellent bactericide, fungicide and antiseptic.  It is used for cattle to kill hoof bacteria and fungus, after all.  If the pond is treated along the perimeter, it is likely that the bacteria in those areas of application may perish, or, at the minimum, will be harmed by the copper sulfate.  However, if the copper sulfate never makes direct contact with the bacteria, that bacteria will remain unaffected.  So, copper sulfate may be used and not harm all of the bacteria if used within reasonable parameters.  Using aquatic herbicides seems to depend on the type and how much is applied.  Speaking only to Sanco’s product, Tsunami DQ (37% diquat dibromide), diquat seems to have little effect on pond bacteria.  In fact, it appears that bacteria may indeed uptake the diquat and utilize it.  Regardless, we caution people to apply the herbicide at a separate date from applying bacteria in order for both products to achieve their respective results.