Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants controlling milfoil

10 acre gravel pit, clear water, average depth 10'-12'. Heavy milfoil infestation. Pretty sure it is eurasian milfoil. I'm thinking grass carp or herbacides for solution. I'm wary of herbacides. Since it's not real deep have been thinking of getting out there with a steel rake and getting as much as I can. During winter it dies off somewhat, and as the water level rises in the spring, it stays about 3 feet under the surface. During the summer it carpets the surface and turns brown and slimy. Impossible to fish from the bank now. Any suggestions?

Grass carp aren't overly fond of milfoil and probably won't bring the infestation under control on their own. However, if your lake meets "containment" requirements for a grass carp permit, you may be able to effectively use them to keep the milfoil heavily suppressed AFTER bringing the problem under control with a single herbicide treatment. I dealt with a similar situation right down the road from you (near Mineola) a few years ago. You may wish to contact that lake's HOA representative to verify their experience with this approach. Email or call me for more details and the contact's name & ph#. KD

I have a 20 acre lake near Ft Worth, average depth 6 to 12 feet with heavy milfoil infestation, worse in spring through fall. I need a solution to get rid of this stuff without killing all my Florida hybrids. Also have some hydrilla which has not been a major problem. What brand of aquacide to use, how much and can it be spot treated so as to not deplete oxygen levels, what time of year.

Check out the label for Sonar. If I'm not mistaken, milfoil is exceptionally susceptible to Sonar so high dosage rates aren't needed. Still expensive, but reasonable. Sonar kills slowly, so it's safe to apply to heavier infestations this time of year. It doesn't work well as a spot treatment, pretty much all or nothing.

Sonar will take out the milfoil at fairly low rates. It is also excellent for controlling hydrilla. It will kill the plants slowly (30-45 days) so you should not have any problems with DO. Email me if you need further help.

SONAR is definitely effective on Eurasian watermilfoil. HOWEVER, our circumstances in the South are considerably different by June 1st, compared to the conditions found in central and northern regions. Our water temps are now in the upper 80's+, untreated plant biomasses are comparatively high by now, and most plants have long-since passed their peak growth-rate stage: all of which will impact the efficacy of SONAR on submerged plant species.
SONAR's mode-of-action is dependent upon post-treatment plant growth - the more rapid the growth, the better the results. As many submerged plants become seasonally mature, they become less responsive to SONAR treatments. That is why early-season treatments (rapid plant-growth periods) of SONAR are far more effective than mid or late season treatments (duckweed is an exception). The optimum SONAR treatment-period is usually dictated by the climatic conditions for the region in question (Feb-May in TX).
So, it is wise to keep the vastness of the US in mind (and the differing regional "seasons") when making treatment recommendations that depend upon a plant's physiological response, which is governed by regional climates and any abnormal fluctuations.
In simpler terms: a SONAR treatment for EWM at this time of the season (in Texas) will be very slow to do its thing – 60 to 120 days before “control” can be expected (lots of patience required). In the mean time, the infestation must be tolerated – and there’s always a risk that when the entire plant population does fall-out (around Aug/Sept), the DO level could go with it (without aeration to offset to O2 demand).
Alternately, AQUATHOL or REWARD could be used to rapidly take down sequential portions of the plant population. But, treat too much, too quickly and the DO will suffer the consequences.
SONAR is usually the less expensive treatment, PER-ACRE-TREATED, when the plant infestation occupies MORE than 25% (+/-) of the pond/lake. But, the pond/lake needs to be relatively static – ie. unlikely to receive flow-through events for 30+ days after a treatment. If it doesn’t fit this requirement (as in Lambo's situation), SONAR is a gamble (especially with ponds/lakes designed for storm water retention). In such cases, the other alternatives should also be considered.