Chitosan vs Pathogens - How it Works

Chitosan is a component extracted from the exoskeletons of crustaceans. It is a naturally occurring substance related to chitin, which is a structural element in many organisms. It is one of the most common biodegradable substances in the natural world. In its natural form, it is found in many strand lengths and varieties, and each variation reacts differently with plants and microorganisms. The chitosan products we use are from a manufacturer who has perfected a process to extract the full spectrum of chitosan from the source shells. It is a medical grade extraction that is safe and usable even for humans.

So, what does chitosan do? The short answer is that it stimulates plants to create the secondary metabolite “chitinase” within the plant. The chitinase destroys the exoskeletons of biting and boring insects as they attack the plant. It also boosts other natural defense systems which allow them to better resist disease and insects. It also stimulates other chitolitic organisms in the soil, on plants, even on the insects themselves. These chitolitic organisms produce chitinase enzymes that destroy pathogenic organisms and exoskeletons of beetles, worms, borers, spiders, aphids, weevil, wire worm, and much more.

That is a nice, simple answer, but how does it work?

Chitosan actually works in different ways, depending on its target, but it universally deters and destroys pathogenic microbes and undesirable insects, while leaving beneficial microbes undisturbed.


Chitosan is directly toxic to pathogenic microorganisms such as bacteria, fungi, and viruses. It destroys the chitin-based structures in the cells, thus killing the organisms. It is not toxic to beneficial microorganisms.


In general, chitosan destroys insects by stimulating other organisms to produce chitinase enzymes, which then dissolve the chitin-based structures within the insects. The method of achieving the results varies depending on the environment.

In the Soil

Within the soil, chitosan stimulates chitolitic organisms which produce abundant amounts of chitinase enzymes. These enzymes come in contact with pathogenic soil organisms such as pathogenic nematodes, wire worms, grubs, beetles, and others. The presence of the chitinase enzymes dissolves all chitin-based structures within these organisms, such as the mouth, legs, joints, and more. The end result is that the enzymes kill the organisms (chitosan, itself, does not).

In the Plant

When chitosan is applied to a plant surface, it readily absorbs through the leaf surfaces. The presence of the extra chitosan stimulates the plant’s natural systems, creating, again, the chitinase enzymes. These enzymes target and eliminate pathogenic microbes within and on the plant. The chitinase enzymes within the plant tissues are also toxic to any insects that try to eat the plant, dissolving their chitin structures and killing them. Insects can also sense the presence of elevated chitinase enzymes and will avoid the plants, searching for less protected plants where they can feast in peace.

On the Insects

Chitosan is not directly toxic when applied to insects. However, even insects are covered in many microscopic organisms. Many of these organisms are chitolitic, but without stimulus, the enzymes produced are not detrimental to the host. Applying chitosan to the insect stimulates the chitolitic organisms that are present, causing them to produce an abundance of chitinase enzymes. When sufficient enzymes accumulate, they attack the host insect and dissolve the chitin structures, killing it. The insect will also carry the chitinase enzymes to its eggs and they will also be destroyed.

When dealing with insects, it is not an immediate process, because we have to wait for the chitolitic organisms to produce sufficient enzymes. However, given a little time (sometimes up to several weeks to achieve full control) and regular application, the chitosan will easily control pathogenic insects such as beetles, mites, spiders, bed bugs, and more.

Pollinators and other beneficial insects are not affected by chitosan in the plants, because they don’t eat the plants. Bees can collect the nectar of treated plants without any harm. Ladybugs can eat aphids from treated plants without any problem. However direct spray applications on beneficial insects could be detrimental. Don’t spray chitosan when pollinators are flying or pollinating.

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