Roundup & Aquatic Weeds

Roundup is the most widely used weed killer in the world because of its effectiveness in eradicating unwanted plants in driveways, lawns and commercial crops. Designed specifically to kill terrestrial perennials or a plant that lives for more than two years, Roundup is not rated for use in aquatic environments.


Aquatic weeds can be managed.
Monsanto's patent expired in 2000.

Roundup was introduced to the consumer market in 1976 by the Monsanto company as a broad spectrum systemic herbicide and has been the number one selling herbicide since 1980. However, in 2000 the company's patent on the active ingredient, glyphosate, expired and stiff competition entered the weed-killing marketplace. As of last year, Monsanto's sales of Roundup herbicide only represent about 10 percent of the company's revenue.

Active Ingredient

The glyphosate molecule was patented by Monsanto in the early 1970s as the active ingredient in Roundup. It works to kill weeds by preventing the synthesis of certain crucial amino acids and relocates itself in the growing points of a plant. The amino acids would normally be used to produce peptides, which are the short polymers that hold strings of amino acids together. Without these, the plant cannot metabolize and create new growth.

Resistant Crops

Some plants have been developed to be resistant to glyphosate, or Roundup Ready, and can be indiscriminately treated for weeds without the risk of killing the crop. The first crop developed with this trait was soy. Other crops resistant to the chemical include corn, sorghum, canola, alfalfa and cotton. Several varieties of wheat are still in the development stages.

Aquatic Impacts

Amphibians can die from exposure to Roundup.

Since Roundup is not rated for aquatic use, it must not be used to kill shoreline vegetation or anywhere near water that receives runoff, despite the fact that the residence time is considerably lower in water than in soil. The European Union classifies the herbicide as toxic to all aquatic organisms, especially amphibians because studies have proven its deadly potential on tadpoles. It can also interfere with metabolic processes in some fish.

Aquatic Versions

Aquatic rated weed killers can eliminate cattails.

Aquatic rated versions of weed killers exist that also use the active ingredient glyphosate. Rodeo, ShoreKlear and AquaStar are commonly used by homeowners and lake management companies to eliminate cattails, torpedo grass and alligator weed without harming aquatic life. These herbicides must be diluted with water and are often mixed with a surfactant, or sticker-spreader, to help the chemical adhere to the plant cuticle. Glyphosate products are typically among the least expensive herbicides for purchase.