We are getting closer to think about treating ponds for weeds as we approach spring. If a pond is infested with a particular weed, it is generally recommended to clean out the weeds with a herbicide application. Sometimes it may take more than one application. Then we will follow with stocking the pond with grass carp. Grass carp can help with many weeds, but may not help with all weeds. Grass carp help maintain smaller weeds, but will not eliminate a weed infestation.
I was asked to look at a common pond weed last week which turned out to be watermilfoil. Watermilfoil is a submergent, perennial weed that has reddish stems that can be branched and two leaf forms. All leaves are in whorls of four to six. The submerged leaves are feather-like and flaccid. This is what we observed. UGA Extension Aquaculture Specialist Dr. Gary Burtle says both liquid and granular herbicide formulations can be used to control water milfoil. Diquat, 2,4-D, and triclopyr all have acitivity. However, with granular applications, 70 degrees water tempuerature is needed for good results.
Here is some more information on Variable-Leaf Watermilfoil.