DEET as an Herbicide

Question:  I have an interesting question for you. Word around the local coffee table, is that using a 40% Deet insect repellent kills weeds… A producer is “experimenting” with it in his lawn and he showed me that it does work. It killed the dandelions, lambsquarters, common mallow, etc. The grass surrounding the weeds looks like it was killed too. However, my question is, will anything grow back at all after it has been sprayed with a 40% Deet?! Is it the Deet that’s killing the plant? Any thoughts, comments?

Answer: DEET, the active ingredient in most mosquito repellant will burn the foliage of most any plant and if sprayed with a heavy dose can completed desiccate even large plants. Years ago growers would spray milkweed with mosquito repellant containing DEET and it would quickly burn the plants down to the ground. Milkweed plants would soon after send up new shoots. Years ago one of the major chemical companies investigated developing DEET as a herbicide but as I recall was too expensive to manufacture and formulate and efforts to register the active ingredient was discontinued

The herbicidal action of DEET is contact and can be considered similar to any contact herbicide like paraquat, Liberty, Cobra, etc. It has limited translocation in the plant so any of the growing points not injured by the spray will develop branches and regrowth will occur. If annual plants are sufficiently covered with the spray then the plants will die but perennial plants like lawn grass, milkweed, and dandelion will grow back from perennial underground roots.

Rich Zollinger

Extension Weed Specialist