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Adjuvants: The Magic Ingredient in Herbicides

July 1, 2016

As much as we may love flexing our green thumbs and nurturing our precious plants, sometimes we need to eliminate other plants from our professional cannabis grows. We typically think of these unwanted plants as “weeds among weed,” which can rapidly spread through a garden and snuff out the plants we’re actually trying to grow.

Herbicides are essential, especially for larger outdoor grow. Pollen and seeds travel by wind, and even greenhouses remain susceptible to a wandering seed blown into an otherwise clean garden area. Herbicides come in all sorts of varieties. Some target specific types of plants, while others kill everything they touch.

Adjuvants, which are chemicals and other agents, give you more control over what your herbicide does and how it does it. Adjuvants come pre-added to some herbicide solutions, or you can add them yourself directly into the solution or into the spray tank. To understand adjuvants and what they do, consider their two types: activator and special-purpose adjuvants.

Activator Adjuvants

Activator adjuvants amplify the herbicide’s effectiveness. They can do this in a number of ways: They can increase herbicide’s adsorption (or adhesion) to a plant’s surface or its absorption directly into the plant. They can prevent the herbicide from degrading under sunlight, or keep the weed killer from simply washing off after a feeding or a bout of rainfall.

Activators work in different ways, depending on what the compound is. Some weaken the wax coating on the plant, allowing the herbicide to easily travel into that weed’s tissues. Others work by exploiting chemistry you’re already familiar with, like nitrogen fertilizers that can combine with herbicides to potentially “burn out” targeted plants.

Special-Purpose Adjuvants

For more precise modification of your herbicides, consider special-purpose adjuvants. These can tweak an herbicide’s buffer, which can prevent the herbicide from naturally breaking down, or the buffer can neutralize the herbicide so it slips past cellular barriers. Other special-purpose adjuvants act as anti-foaming agents, or they can enhance compatibility between two herbicides that normally can’t mix.

When using sprays, consider a spray-drift adjuvant. These chemicals keep the spray droplets closely packed together, so more herbicide ends up on the weeds rather than flying randomly through the air (and being wasted).

Which Adjuvant Should You Use?

The type of adjuvant you use and how you use it, depends on what you’re trying to accomplish, what kinds of weeds you’re trying to control, and what equipment you’re using to deliver the herbicide. Remember to always observe proper safety protocols and to wear your personal protective equipment while mixing.

For more detailed information about adjuvants, check out William Curran’s article on the topic at Penn State University’s website.

If you’re serious about adjuvant use, and you’re already familiar with how to use them, consider picking up a copy of the Compendium of Herbicide Adjuvants, 13th Edition.


By Randy Robinson
Cannabis Cultivation Today articles are for informational purposes only and should not be considered legal guidance or advice on grow practices. You should contact an attorney or a qualified cultivation consultant for specific compliance and cultivation advice.


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