Alligator weed is a highly invasive and destructive weed that can invade ponds and nearby land. It tends to displace both beneficial crops and the native fauna. When it grows in water, it often covers much of the water surface and can disrupt the flow of water in the pond. Because it is not native to North America, any population that is encountered should be treated.

Mechanically Removing the Weed

Alligator weed is sometimes eliminated by cutting it. However, this is ineffective because the weed will usually grow back quickly. Use a rake to pull the weed mats toward you. Remove as much of the weed as possible because any weed that is left behind will send out more roots that will reestablish the plant. 

Killing the Weed with Herbicide

Before applying a herbicide, purchase safety goggles. Choose a day that isn't windy, since wind can encourage the herbicide spray to drift and can cause you to come in contact with it.

Systemic herbicides are the best treatment because they will work through the alligator weed and kill the roots. When applying an aquatic herbicide, measure out the proper amount based on the number of gallons of water that you anticipate treating. The herbicide is usually applied by spraying it into the pond. Many herbicides are contact herbicides that are only effective if a portion of the alligator weed is exposed. Therefore, the herbicides should usually not be applied if the plant is completely submerged.

Make sure that you time the application of the herbicide properly. For example, Isopropylamine Salt of Glyphosate needs to be applied when the weed is in bloom. Apply your herbicide when the water temperature is 60 degrees or higher. If you aren't sure how much herbicide you should use, talk with a place like Snyder's Weed Control.

Treat the pond in sections rather than trying to treat the entire pond at once. Adjust the spray nozzle so that it will allow you to have good enough coverage without concentrating the herbicide too much in one area.

Cleaning Up Afterward

As the alligator weed browns, you should remove it or the weed will accumulate at the bottom of the pond and turn into mulch. By eliminating the conditions that encourage the growth of more alligator weed, such as water containing decaying matter, it will be easier to bring the problem under control. The weed will mostly be gone within two to three weeks, but you will need to check regularly to make sure that it has not grown back.