I need help in eliminating/controlling American Pondweed. We tried Sonar AS @ 40ppb and struck out. Zero results. The next year (2006) we tried Sonar AS @ 90ppb on the advice of Sepro (manufacturer of Sonar) and struck out again. Zero results. Last year, I gave up in frustration. Back at it this year. Any help or advice on how to deal with this weed will be greatly appreciated. Thanks.

Are you sure it's American pondweed?
http://aquaplant.tamu.edu/database/submerged_plants/american_pondweed.htm

Treatment options:
http://aquaplant.tamu.edu/database/submerged_plants/american_pondweed_mgmt.htm

Have you tried Reward (diquat)?

I had some American Pond weed along with my crop of Elodea.

I used a mixture of Reward and Cutrine Plus and had fantastic results on both the pond weed and elodea.

The second link above recommends this mixure.

I have eliminated it quite often with grass carp. Can you get them in California?

Thanks for the responses & suggestions.

Shorty, the plant has been positively ID'd as APW by both UC Davis Ag Dept. and two chemical manufacturers.

Jeff, I have tried Reward on an experimental basis. The infestation of APW is so dense that there is no practical way to get the diquat in contact with the entire plant surface as recommended. This weed is growing in water depth to 11 feet and each stem is covered with algae. The Diquat was somewhat effective near to shore where the plant was fully in contact with the chemical due to the shallow water. Of course, the Diquat is not a systemic, but a contact weed killer, and,therefore, does not kill the root system. At least that is my understanding.

Dave, the grass carp in not an option as there is a
flow-through creek which runs up to 6 month out of the year. CA Fish & Game will not issue the needed permit in situations where a flow-through creek exists.

I paid close to $1,700 per gallon for the Sonar AS since the systemic herbicide seemed like the best way to go. I have had zero luck so far dealing with Sepro in an attempt to be made whole by Sepro, either with a refund or with additional product at no cost. The Sepro West Coast rep recently visited the ponds and could not believe the amount of weeds I am dealing with. He said the Sonar "should have worked". I told him "it didn't. How about some help?".

We are into this about $5k now for the 3 gallons of Sonar with nothing to show for it. Any additional ideas by anyone experienced with APW will be greatly appreciated. Thanks.

Did the water flow-through effect your Sonar application? Aquathol worked better for me than Reward. It does not kill the roots and the stuff comes back. Glyphosate and Habitat applications did not work. Removal by track-hoe may be and option to reduce them to a measurable amounts then by chemical methods.

Wow ohmanlee, I had no idea that American pondweed grew to those depths, I always assumed it was just a shallow water plant. I would still go with the Reward, cutrine plus, and would then amp up the mixture with a surfactant too. I would put down a treatment every two to three weeks until it was knocked out. My understanding is that with Sonar you can't have any water flow though otherwsie the treatment won't work like it is supposed to. A good down pour and flushing will ruin the Sonar treatment.

Thanks, ewest. No, the flow through is not a factor, as I waited until the pond had stopped spilling for the season before using the Sonar. Sepro tested the water 16 days after application and said the ppb was as required. The Sonar made the APW sick (whitish, pink color to the leaves) but could not kill it as advertised.

My latest idea is a tool called a Weed Razor, which cuts a 4 foot swath through the vegetation, which then floats to the surface. Quite a bit of work, but with two 14 year old helpers and two Weed Razors, I cleared one entire one-acre pond last Friday. We cut and removed 90% of the vegetation in the pond and I am now waiting on Sepro to come across with some chemical to treat the pond again before the re-growth gets too thick.

Shorty,
The APW will grow in water even deeper than 11 feet, if the water is clear enough for the light to penetrate to the pond bottom for seed germination. Our pond is 13' in depth in the deepest place. No weeds in that small area, as the water is not clear enough.

We don't get enough rain in the summer (usually zero) to be a factor. Sonar is actually used by some irrigation districts in their canals with continuously flowing water. They meter it in at higher rates, up to 130ppb, to maintain the target amount of chemical in the water.

The irrigation districts must be metering the dose during periods when the water will not be used for irrigation, since SONAR has a 30-day(+) irrigation restriction (unless below 10ppb, and only for established turf).
AQUATHOL SUPER K (endothol on polymer granules) might be your best bet (and hopefully not a third strike). Then again, I'm puzzled why the SONAR didn't perform.
Do you know the scientific name of your specific plant? Several rooted/emergent plants with eliptical leaves on the surface are often called Americal pondweed (sometimes incorrectly).

ohmanlee.....I just purchased a weed razor to remove illinois pondweed from my 1 acre pond. It is 95% pondweed. I just started using it and it works great. I think a long weekend and a few nights I can have it cleaned up. What did you use to get the floating weeds out of the pond? For me that is the tough part.

I watched 4 Grass Carp yesterday afternoon in my pond munching on APW like cows grazing. Now, if they would go after the chara...