There is a common misconception that using dish soap as a surfactant in your insecticide or herbicide will increase its effectiveness. Using a surfactant will dramatically increase the effectiveness of herbicides, insecticides, and many other garden chemicals. In an attempt to save money, some people will use a liquid dish-washing detergent in place of a commercially manufactured surfactant. We do not recommend it, and here are the reasons why.
Understanding the differences between using a true surfactant versus using dish-washing detergent as a surfactant.
The easiest way to explain a surfactant is that it makes water wetter. Surfactants are compounds that lower the surface tension of a liquid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants.
The lowering of the interfacial tension between two liquids can increase the effectiveness of your weed killer up to 3x’s. This allows you to achieve control of weeds faster and with fewer applications.
A true surfactant will promote absorption of the chemical into the plant. The opposite could be true when using a dish-washing detergent since it could potentially block the chemical from penetrating into the plant.
Although using dish detergent was commercially recommended by major garden chemical distributors back in the 70’s, technology has changed. It has recently been deemed possibly ineffective for herbicides and insecticides.
The active ingredients in dish detergent are intended to break down chemical bonds in oil and organic based compounds. Adding dish detergent to your weed killer could tear apart the molecular structure of the chemical, making it less effective in killing weeds. It is possible that adding a dish detergent to your weed killer as a surfactant could increase the adhesion of the chemical to the leaf of the weed. It just would not increase the effectiveness of the weed killer in killing the weed like a true surfactant would.
Zamzows recommends a true surfactant specifically formulated for garden chemicals, like Zamzows StayPut spreader sticker. Zamzows StayPut is a combination spreading/sticking and penetrant agent designed to provide better distribution and adhesion on the leaves of plants with all types of herbicides. It can also be used with insecticides and fungicides. Like dish detergent, StayPut helps your chemicals stick to the leaf of the plant and spread out evenly on the leaf to maximize effectiveness. However, it will not break down the chemical bonds in your herbicides, insecticides or fungicides.