Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants getting rid of hydrilla

Our 22 acre lake is full of hydrilla. What's the best way to get rid of it without hurting the fish? I thought about putting a cable between two boats and dragging the lake. Any suggestions?

Triploid Grass Carp will control it...dragging a cable won't do much good at permanent control, might do more harm than good...the other alternative is chemical, plenty of herbacides available out there that will eradicate the stuff...Kelly at Estes Inc. can probably help with the chemical solution...however, personnally, I'd use a FEW TRIPLOID grass carp, some hydrilla is a good thing for your food chain. I've seen and been on lakes where the "grass" was eradicated using "regular" grass carp, the LMB fishery plummeted as the grass disapeared !...

I really appreciate you for the suggestions. I think a few grass carp would help a lot. The vegetation level is about 80% coverage with hydrilla, which is way beyond the recommended 15-20% by Bob Lusk (a.k.a. Dr. Pond Boss). Our lake is getting pretty shallow from all the decayed hydrilla. Maybe we could dredge a channel in it or something to provide some deeper water.

Nearly all of the LMB's are in the 13 to 16" range, with a few larger ones or fingerlings less than 5" long. We are considering culling some of the 13-16ers out. Thanks.

Several comments to be made here.
1) Some aquatic vegetation is generally regarded as being good for a pond or lake's fishery. However, having a little hydrilla is akin to having a little cancer, and equally risky if left unattended. Hydrilla is not a plant specie that typically self-regulates its density within the acceptable level of plant coverage. It is an extremely invasive specie in most water bodies, the exception being lakes that experience widely fluctuating seasonal water levels.
2) Herbicides will NOT "eradicate" hydrilla on their own. Due to its various means of propogation, hydrilla is a very tenacious specie. Though it doesn't sexually reproduce, it is quite capable of rapidly expanding its population through fragmentation, and producing turions and tubors - see pics > Hydrilla Pics . It is the later two structures that are not likely to be impacted by herbicide treatments. Therefore, herbicides are generally considered a temporary control measure (1-5 yrs).
3) In my opinion, LMB populations do not fluctuate as a direct result of hydrilla control. BUT, an indirect result of hydrilla control on public waters may be that catch-n-keep fisherman become more successful due to easier navigation and/or shoreline access. Secondly, the LMB population often becomes scattered - rather than concentrated along the weed lines - making frequent hookups less likely. The net affect of both might make a lake appear to be less populated with fish. In most cases, creel surveys show a dramatic increase immediately after a vegetation reduction. Two popular trains of thought: LMB now have easier access to their forage (hence faster growth-rates), and fishermen have easier access to aggressively feeding LMB (higher catch-rates). Bottom line: LMB populations don't "disappear" in the absence of hydrilla - unless they leave by boat or vehicle.
4) Grass carp on their own, at normal stocking levels, will not bring a severe hydrilla infestion under control. Conversely, stocking too many grass carp may denude the lake of all vegetation for years to come - not a good option. However, using a "hydrilla selective" herbicide treatment followed by a modest stocking of grass carp may be the best plan for controlling and managing the hydrilla population to a more desirable long-term level, or converting the lake's hydrilla mono-culture toward a more diverse and desirable (less invasive) group of plant species.

As for the 22-acre lake in question, the "best solution" requires more details of the lake's unique characteristics. I would be happy to discuss your situation if desired. Otherwise, I would suggest hiring a qualified lake/fisheries biologist in your area to review and advise toward a viable long-term solution to the hydrilla infestation.

Thank you so much for your comments. What would be the conservative recommended # of triploid grass carp per acre for a lake about 4 feet deep?

I have also thought about drawing down the lake to put on the herbicide. My understanding is herbicide will not kill the hydrilla under the water, but only that touching the surface.

Drawing down the lake for a herbicide treatment would likely be counterproductive - but depends greatly upon which herbicide will be used and your overall game plan.

Hydrilla tubers and turions can survive on/in soils for quite awhile. So, if you draw down the lake, then treat the water - the plants in the water may be controlled. However, the tubers and turions above the water line will likely begin to grow unimpeded as soon as the pool level has been re-established.

It might be a consideration to draw down, then treat with SONAR, while also adding 3-4 grass carp per pool-level surface-acre. Let the SONAR control the hydrilla that remains in the water (less product would be required in the reduced volume of water). Then, the grass carp might be able to keep the pool-level perimeter growth in check after the water-level has been elevated.

You can alway add more grass carp - if deemed appropriate. But, if you start out with too many, it is quite a challege to get them thinned out.