DMA-4 is a liquid 2,4-D product that is mainly used for the control of Eurasian watermilfoil, as least here in Minnesota. So, the question is: Should I used Hydrothol granular or a 2,4-D product if my main aquatic plant is milfoil? The answer is: It depends.
Contact time is needed when using 2,4-D. If you have a small area you are treating, and it is exposed to wind, then no, you should not use it. If you are treating an area that is protected in a bay or channel, or you are treating a large area, then you can start thinking about using it. Though you need to consider dose as well, generally it takes 24 hours of contact time for it to work.
So, why use a product like DMA-4 instead of Hydrothol? There are two good reasons. First, DMA-4 is a systemic herbicide that will not only kill the plant, but the root as well. Hydrothol will only kill the plant, allowing the plant to re-grow shortly after it dies off. Second is cost. 2.5 gallons of DMA-4 should treat a bit more than two 40# boxes of Hydrothol.
DMA-4 can also be used to control waterlilies. A little will go a long way here. Of course, check with your local authorities to see if you need a permit to apply this product. Lakes in MN do require a permit to use this product! If you are still unsure which product to use, please give us a call at 763-463-0365.