We have a 1/4 acre spring fed pond with average depth of 8 feet (12 maximum). Intermittently, duckweed and filamentous algae have been a real problem. Last year, May through November the entire surface was covered with duckweed.
We use our pond to irrigate about 1 acre of organic blueberries. I would like to stay away from chemicals in general, although I have used pond dye in the past with little success.
Questions:
Has anybody used herbicide in this situation? If so, what? Needless to say, anything that would harm our crop would be a strict no-no.
I'm currently putting together an aeration system. How much of the duckweed and algae problem with this take care of by itself? I've been lurking in the aeration forum for a while, and have a pretty good idea of what I want to build, but haven't seen much detail on the success of aeration alone to control algae.

Thanks for the help.

Check to see if Tilapia are legal to stock in the pond in your state. If they are, then I'd stock 20-30 pounds. Aeration by itself won't fix the problem.

Great idea!
Tilapia farming is legal in Tennessee and there is, or was, a farm very close to us.

I like all of the non-herbicide solutions first, but sometimes you can achieve better living through chemistry.

Purdue put out a good article on control of duckweed:

Control of Duckweed and Watermeal

One of their non-herbicide recommendations is to reduce nutrients to the afflicted pond. Do you use any organic fertilizers on your blueberries that might wash into the pond? If so, then diverting this nutrient-rich surface flow away from the pond could reduce your duckweed problem.

They also make herbicide recommendations. There is a good "contact" herbicide (diquat) and a good "systemic" herbicide (fluridone).

I would recommend trying the diquat first and seeing how much control you can achieve. The treated pond is then safe for irrigation after 5 days.

The systemic treatment fluridone would probably give you better, longer-lasting treatment. (Sometimes the duckweed control may carry over to the next year.) However, the treated water cannot be used on irrigated edible crops for 30 days. It also cannot be used within 1/4 mile of drinking water intake pipes.

Hopefully, you can beat back the duckweed and FA with tilapia and other means. But you can probably use the diquat for assistance if your blueberries can take a week off without irrigation.

Good luck on your project!