Either from shore will be tough to get an even coverage without a boat. You need to apply it evenly over "X" area at "X" rate. One person in a kayak not being able to move the kayak while working the spreader makes it hard to get even coverage unless it's an electric or battery powered spreader.

I'd have to look up the label to see what the application rates are, but you need to follow what the directions on the label say to do for application rates.

I have a tank sprayer that I have in the boat, and I can use weighted lines on a boom to get the herbicide down to the plants while the boat is under motor power.

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