Weather conditions often dictate “what, when, and how” aquatic algaecides and herbicides should be applied. To ensure proper efficacy, pond products should never be applied during rain or immediately after rain events. Algaecides/herbicides have minimal contact times that must be met in order to be effective. Even a light rain shower can wash the product off of its intended target. You want to keep the product on the pest and prevent off target movement onto desirable species, landscaped areas, or into groundwater.
Wind speed and direction dictate proper application of pond products. In fact, most labels prohibit the use of herbicides in winds greater than 10 mph. This is because they can damage desirable landscaping such as grass, trees, shrubs, etc. It is important to always read the EPA product labels prior to use. The LABEL IS THE LAW!
Fish Kill Due to Over Treatment
Extremely hot weather increases the risk of fish suffocation due to low dissolved oxygen. Decomposing algae/submersed weeds can further drop the dissolved oxygen. When treating expansive areas of algae or weeds with contact products, it is important to treat the pond in sections. For example, treat only a third of the pond at a time and maintain a 14-day interval between subsequent treatments. Again, these sectional treatments are often required by label law. This treatment method will prevent widespread oxygen depletion due to decomposition. Furthermore, there are times of the year when all algaecide or herbicide applications should be placed on temporary hold. These are the dog days of summer when we have extended streaks of 100+ degree days with little or no wind and minimal rainfall.
Cold weather can also impact the efficacy of aquatic products. Some products have a minimum water temperature at which the product will be effective. Most product labels specify that the pest must be “actively growing” at the time of application. If the pest is dormant, then it will not uptake the product and result in wasted product and misspent funds.
And finally, algaecides and herbicides are most effective when applied on sunny days. Algae and aquatic weeds require sunlight for their normal biological processes. The active ingredients in aquatic products disrupt these biological processes to ultimately eliminate the pest. Therefore, a pest growing under normal conditions (direct sunlight) will most efficiently uptake the product.
If you are unsure of “what, when, and how”, we recommend that you contact a qualified lake management professional.