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Smartweed growing along the edge of a pond

We have been looking at many ponds and aquatic issues this week and last. We’ve been talking about pond water samples and liming as well as weeds. In this pond, one weed species was a primrose – that if you see during the season, has a yellow flower. It can be mistaken for alligator weed which has a white flower. Another common pond weed, smartweed, was growing along the edge. UGA Extension Aquatic Scientist Dr. Gary Burtle says that a 1.5% solution of glyphosate with surfactant would be effective on both of these weeds. The issue we are having is timing. As plants are shutting down and weather turns cold, treating an infested pond at this time is not a good idea.

When is too late to treat aquatic weeds?

UGA Extension Aquatic Scientist Dr. Gary Burtle says our water is borderline for treatment right now. 70 degrees F is when we are generally safe to treat ponds. We still need to consider, however,  that some compounds work better at 80 degrees F though 70 is our cutoff. Right now, plants are not growing as fast, and chemical reaction is slower.

What does this mean? Some of our compounds are systemic and others contact. Diquat, cutrine and clipper are contact herbicides. Sonar, which is good on watermeal and duckweed, is systemic. Systemic chemicals needs 3 – 4 weeks of actively growing plants to be effective. We are certainly too late in the season for this kind of treatment. Clipper also works good on duckweed when watermeal is mixed. But the issue with contact herbicides is though they may provide a kill with borderline temperatures, timeliness is key. If we do not already have a plan, water temperature could drop to 60s in a short time.

We must to also consider pond converge. Dr. Burtle reminds us that if the pond is 80-100% covered, two treatments of a contact herbicide would be needed. Considering the cost, one application of a systemic herbicide (for a small pond < one acre) would be less expensive – which we are too late to apply.

Conditions now are essentially the same as conditions will be in late Febrary. At this time in the season oxygen in a pond is actually higher. This will keep us from losing too many fish and should also be considered. Cooler weather will also slow weed growth. Dr. Burtle says it is not totally bad to treat during these conditions; however, once all factors are considered, waiting until spring would be more beneficial.

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