Diquat is a contact aquatic herbicide, meaning it kills plant tissue on contact rather than moving inside the plant. Because it acts where it touches, it can rapidly knock down vegetation that sits on the water surface (floating-leaf plants), as well as submerged aquatic macrophytes and even algae that come into contact with treated water. This broad action is why it’s used to control multiple types of aquatic growth quickly, so the best choice includes floating-leaf vegetation, submerged aquatic macrophytes, and algae. Other options restrict the target to terrestrial weeds, submerged plants and algae only, or emergent plants, which doesn’t capture the full range diquat can affect.

Fluridone works best when it is distributed across a large, relatively still treatment area so it remains in the water long enough for plants to absorb it. Flowing water moves quickly, dilutes the chemical, and carries it downstream, which makes it hard to achieve uniform coverage and effective control. Spot treatments in moving water create patchy results and can require extra applications, defeating the purpose of the slow-release, broad-area approach. Large-scale or whole-lake treatments align with how fluridone is meant to be used, with low concentrations over a longer contact time to achieve systemic uptake by the plants. And always applying within the annual limits based on acre size ensures you stay within label guidelines and protect non-target organisms.

In deep, poorly lit, and poorly oxygenated water, light-driven breakdown and many microbial (aerobic) degradation processes slow down. That means the pesticide is less likely to decay quickly through those pathways. At the same time, some pesticides have a tendency to bind to sediment particles. When a compound binds strongly to sediment, it is less likely to move with the water and leach into deeper water or groundwater. For imazamox, this combination of conditions means it will tend to stay associated with sediments rather than being carried away by water, so it shows limited leaching due to sediment binding. It’s not typically volatile, and hydrolysis isn’t expected to be rapid under these specific conditions, so those pathways don’t drive the fate as much as sediment binding does in this scenario.

Copper algicides act quickly on simple algae because these tiny, exposed cells take up copper rapidly, leading to rapid disruption of photosynthesis and cell function. Larger aquatic plants, or macrophytes, respond more slowly because they have bigger, more complex tissues and slower growth, so the copper takes longer to reach enough of the plant to cause visible stress or tissue damage. For macrophytes, you typically see noticeable effects after about one to two weeks, though exact timing can vary with growth stage, water chemistry (like pH and hardness), temperature, and how the plants are taking up copper.