I know that it is almost always recommended to apply chemicals when the water temp is around 60 degrees because of active plant growth and chemical uptake. Could algae be treated, say with cutrine, when the water temp is in the 40's, but a couple of "warmer" days have caused a good amount of algae growth in the shallow areas?
Just curious.

I applied Copper Sulfate days after my ice melted off my pond and it killed it, not sure what the water temp was, but I'm sure it was under 50 degrees.

Mike

If the plant, or in this case algae, is actively growing you will be able to control even in cooler weather.