We have a 12 acre lake consisting of 3 connecting sections. The lake has been treated with Sonar at the rate of 1 gallon liquid, 15 lbs fast acting granules,and 10 lbs of slow release. I was first told the grass would be gone in 60 days. It now has been 90 days and we still have the grass. Is this going to work? What do we do now? Thanks.

John,
I recommended a similar treatment for coontail in a 4 acre pond near Bellville which is having similar results; not to mention another larger treatment near Port Arthur that eventually worked - but only after a LONG time (90 days).
This has been an abnormal season for coontail. Normally, it is one of the first plant species to die following a SONAR treatment. The rates used in your pond sound good to me. I'm scratching my head too.
Some questions for you: When (date) were the treatment(s)applied? Were they applied at the same time, or sequentially? Did you experience any flow-through events during the first 45-60 days following the treatment(s)? Was your water relatively clear, or was it murky/turbid? Did you ever notice any discoloration on the plants' growing points?
I'll explain the significance of these questions after viewing your responses.
In the mean time, it may be a little risky to try too much corrective action at this point - especially when it MIGHT not be necessary. Killing too much plant-mass during hot weather can be a problem for your fish.
I'll look forward to seeing your responses.
Kelly

John,
As a fisheries biologist and consultant, I have occasion to work with different materials to treat plants.
I have used Sonar to successfully eliminate coontail. It took 85 days.
Measuring the lake was critical, both surface acreage as well as average depth. As much as Sonar costs, we wanted to be sure the volume of water we were to treat.
Sonar was applied May 1 that year, and ends of coontail quickly turned pink. But, the plant didn't die in that 13 acre lake east of Dallas. I watched it, sweated, wringed my hands. (It was my first ever Sonar treatment) Weekly trips to the site, questions from the landowner we tempered with confidence from the Sonar rep who guided us through that first treatment. Finally, July 25, there was no trace of coontail at the surface, anywhere. It had starved itself to death, fallen to the bottom, where it was decomposing.
A big sigh of relief, and a healthy pond were the results.
So, if you have done your homework, measured the lake accurately, used the recommended amounts of Sonar, keep the faith.
If not, watch for Kelly Duffie's response to your answers. You may need to follow up with plan B.