Hi squeeky.
I'm an agricultural engineer and I talk to you about my knowledge of herbicides and lotus (nelumbo nucifera; the american lotus is nelumbo lutea but it's similar).
In my opinion you can efficiently use the 2.4-D in liquid form, taking care to mix it with a special surfactant that allows the product to stick to the water-repellent lotus leaves, otherwise the herbicide would end up in the pond water without results.
2.4-D is a systemic herbicide, so it is essential that is absorbed by the leaves to be translocated to the rhizomes.


Filippo