Todd: Never heard of OPTI-AMINE, but suspect it is a formulation of 2,4-D Amine - which is completely ineffective on duckweed, as is glyphosate (in case you should ask).
As for diquat (REWARD) or fluridone (SONAR): IF the pond is static or has very little potential for a flow-through event, and IF more than 50% coverage (assuming at least 1 to 2+ acre pond size), I'd lean toward using fluridone - especially if your application equipment is limited to a low-volume (hand-held) pump-up sprayer. On the other hand, IF your pond regularly experiences flow-throughs/over-flows, or has a high likelyhood of same with minimal rainfall, REWARD may be your only practical option. However, it is best to conduct REWARD treatments before the infestation reaches severe levels, since REWARD must contact all plants that are expected to secumb to the treatment (add CIDE-KICK to REWARD to increase it activity on the targeted plants). With REWARD, use the wind to your advantage. Treat (with the wind behind you) from a boat (pref a 12v ATV type sprayer) when the wind has the duckweed concentrated along a windward shoreline. Strive to contact as many of the duckweed plants as possible with the initial treatment (2 gal. REWARD per TREATED surface acre, diluted in enough water to allow thorough coverage). Conduct REWARD RE-treatments to surviving plants within 3 - 6 days. Otherwise initial-treatment survivors will quickly replace what plants were successfully controlled. Multiple duckweed re-treatments are the norm with REWARD, though each successive treatment should require much less product and time than the prior treatment. Use clean water ONLY when tank-mixing REWARD (muddy water ties up with diquiat very rapidly).
SONAR usually requires only one whole-lake treatment - dosing at 6-8 oz. per acre-foot (under conducive circumstances). Satisfactory control may last beyond one season, unless a reintroduction of the plant should happen, or a flow-through event occurs within the first 30 days after the treatment. SONAR requires this 30-day length of contact-time to impart its effect on susceptable plants. SONAR applications require only a bucket or pump-up sprayer. SONAR's dilution-ratio in the mix-tank is irrelevant - the proper dosage is based on amount of undiluted product in relation to the volume of water in the pond. Focus on achieving and maintaining the targeted concentration for at least 30-days (measure in parts per billion - ppb).
Unlike REWARD, fluridone is applied INTO the pond's water-colume as a properly-dosed pre-diluted solution (Do not apply fluridone solution on top of duckweed infestions. Direct sunlight quickly breaks down fluridone). Alternately, REWARD must be applied as a topical spray to all targeted plants.
Lots of "ifs" and requirements to consider in this thread. Any questions? Let me know.
KD
