A Review of Lake Weed Control Products

May 28, 2022

There are nine types of lake weed control products and methods. Of these, I have three categories — Effective, Neutral, and Makes Weeds Worse.

EFFECTIVE

NEUTRAL

In some limited, extreme cases where drawdowns can’t be done and invasive lake weeds have taken over larges areas of a lake, I concede the “temporary” use of “professionally applied” herbicides, only until proper lake management practices can be employed. (I do not recommend the private use of “lake weed pellets”).

I’m neutral on grass carp, milfoil weevils and other insects touted as lake weed eaters. They’ve had some success, but not consistent success.

MAKES WEEDS WORSE

I do not recommend manual removal. Commercial harvesting creates more weeds on a very large scale. Limit hand raking and cutting — it creates more weeds.

I do not recommend sediment agitation — it creates more weeds, though not as bad as commercial harvesting.

I strongly do not recommend rotovation — the list of negatives is very long.

Following is a description of all lake weed control products or methods — appearing in alphabetical order.

Aeration

Aeration is the process of putting more oxygen into a lake. As I’ve written many times elsewhere on this site, aeration is one the best things you can do for your lake.

It won’t kill off many lake weeds, but an aerator will make the area around it much healthier. More oxygen helps good bacteria multiply and digest more dead plant matter, more quickly.

Aeration is good for fish and other aquatic animals, providing a healthier environment and creates more food down the food chain. It hinders algae blooms and helps remove toxic gases like hydrogen sulfide from the water.

Aeration can also cut down on mosquitos by creating a flow in stagnant water. Aeration is awesome — and you may even have fewer lake weeds.

Biological Control (milfoil weevils)

A surprisingly old method of lake weed control is the introduction of organisms like the milfoil weevil, which feed on invasive lake weeds. The milfoil weevil is probably the most successful example of using biological control to deal with a specific invasive weed, in this case, Eurasian milfoil.

Though this lake weed control method — using insects to control invasive plants has been used for a century, it’s not in widespread use at this time. On some lakes, weevils have been effective — on others they haven’t.

Grass Carp

This fish is considered an invasive species, but it is stocked in several states as a lake weed control option. These carp feed primarily on Eurasian milfoil. Carp used for lake weed control in lakes or ponds are sterile. In some cases, grass carp have been effective at controlling some lake weed populations. In other lakes they’ve failed to control weed growth, or they’ve eaten other native plants.

Herbicides (Pesticides, Chemicals, “lake weed pellets”)

The most common lake weed control products are the aquatic herbicides. They use various methods such as weakening plant cells and preventing uptake of nutrients.

There are many drawbacks, toxicity, oxygen depletion, creating “resistant” lake weeds, adding to sediment build up — the list is long.

Yet, herbicides are the most commonly used lake weed control products to treat whole lakes — it’s sometimes necessary.  The term “lake weed pellets” refers to home use herbicides. These pellets, often spread by hand or hand-held spreaders, are granular (often weaker) versions of professional lake weed control products.

Lake Drawdown

In lake drawdown weed control, the water level is lowered as a method of lake weed control. Water drawdown in winter exposes shallow lake bottoms to both drying and freezing, which can kill off lake weeds in shallow areas.

Once the lake is lowered, lakefront owners can get to their lake bottoms easily and remove dead weeds, clean things up and it’s a great time to install lake weed control mats.

The drawbacks of lake drawdown weed control — You have to be on a lake with a dam that can be opened to let water out. And freezing the sediment kills hibernating animals such as frogs and turtles — unless the drawdown of the lake is done before hibernation begins.

Lake Weed Control Mats 

This consists of placing a barrier between weeds and the lake bottom depriving plants of essential sunlight and preventing seeds from spouting. LakeMat Pro is this type of lake weed control product.

Lake weed control mats are the single best method of lake weed control for small areas like personal waterfront beaches and around docks and lifts. They are easy to install, pro-green, don’t harm fish and use no chemicals.

The drawback is — they need to be cleaned annually to stay effective. Cleaning can be done right in the lake with a broom.

Manual Removal (Harvesting and Raking)

This covers a wide range of lake weed control products, from hand-held, lake rakes and lake weed cutters, to commercial lake weed harvesters. The method is straight forward —physically remove lake weeds and dispose of them.

The biggest issue is fragmentation — creating thousands of small weed fragments that quickly settle, take root, and start growing new plants. Here’s a harvesting horror story…

A lake in Minnesota had milfoil on one small part and none anywhere else. A harvester was brought in and removed the milfoil. Small weed fragments broke off from the harvesting floated all over the lake — today the entire lake is covered in milfoil.

Rotovation

Rotovation is sediment agitation combined with an underwater rototiller blade that pulls out lake weeds and disturbs the sediment on the lake floor. Commercial machinery is used for this type of management.

It’s expensive, causes massive weed fragmentation and weed re-growth. In fact, there are so many negative consequences to rotovation, (you can look them all up, if you like) it is seldom seriously considered for lake weed control today.

Sediment Agitation (Weed Rollers)

Sediment Agitation consists of keeping a waterfront area agitated with a weed roller or other device which separates the nutrient-rich sediment from the sand and heavier soils of the lake bottom.

A simple version of this is slowly engaging an outboard motor while the boat is secured to a dock. The prop wash blows plants and soft sediment out of a small area very quickly.

Again, the big issue with this lake weed control product is it creates hundreds of plant fragments that quickly settle, take root, and start growing new plants — which creates an on-going problem.

— Doug Fast