How to use Trichoderma to fight fungal diseases

Trichoderma is a genus of soil-dwelling fungi found around the world that are highly effective in colonizing many types of plant roots and inhibiting fungi that cause many types of disease. It was one of the first types of biofungicides to be commercially available.

One strain in particular, T. harzianum T-22, is the culmination of 15 years of research at Cornell University to create an even more potent type of Trichoderma.

Strain T-22 forms an intimate association with plant roots and colonizes them. This colonization puts the fungus in a good location to outcompete and parasitize other fungi in the soil.

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This fungus can inhibit a who’s who of fungal soil pathogens, including Fusarium (wilt), Rhizoctonia (root rot), Sclerotinia (fire blight), and Pythium and Phytophthora (damping off).

Trichoderma works best on plants that are not doing well. If your plants are already at their peak, you may not see any effect from adding this microbe.

However, if conditions are not optimal, yield increases range from 10-20% to as much as 300%.

The guide below describes exactly how this fungus improves plant growth and gives you tips on how to best use it.

How Trichoderma interacts with plants

Colonization of plant roots

Once in the soil, this fungus colonizes the roots of plants. By growing on the roots and in the rhizosphere, it forms a physical barrier to prevent the growth of fungi that would otherwise cause disease in the plant.

Plants often produce chemicals to defend themselves, and Trichoderma is resistant to many of them, allowing it to colonize the roots. And it does this without interfering with other microbes that help the plants, such as mychorrhizae or Rhizobium (bacteria that fix nitrogen).

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Trichoderma can improve plant health even in the absence of pathogens. The fungus grows best in acidic soil and helps create such an environment by secreting organic acids.

These acids have an additional effect that greatly benefits the plants: they can dissolve phosphates and mineral ions, such as iron, magnesium and manganese. This means that they facilitate the dissolution of these minerals, making them easier for the plants to absorb. Such nutrients are often scarce in the soil.

The increase in the yield of the plants is greater if the soil is really poor to begin with.

Stimulation of plant defense mechanisms

You may not know that plants have an immune system. They are able to sense invasion by pathogens and activate cascades of reactions to produce chemicals to protect themselves.

Trichoderma has been shown to activate plant defense responses, allowing the plant to fight some infections above ground, but their effects are not limited to soil pathogens alone. An example is Botrytis, a debilitating above-ground fungus that is sometimes controlled with Trichoderma.

How Trichoderma interacts with other microorganisms

Part of what makes Trichoderma such an effective biological control agent is that it uses a variety of mechanisms. That makes it very difficult for its target organisms to develop resistance, as they would have to develop resistance against a number of different mechanisms at the same time.

Parasitism of other fungi

Trichoderma can directly parasitize other fungi. First, it attaches to it. Then it coils around them, producing structures that can penetrate them. In addition, this fungus produces enzymes that break down the cell walls of the fungus. This process is known as mycoparasitism, where myco means fungi.

Most fungal cell walls contain chitin, and strain T-22 in particular produces large amounts of an enzyme called chitinase that can break down the cell walls of its opponents.

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Trichoderma protects itself against the chitinases it produces.

Production of antibiotics

In addition to physically parasitizing other fungi, Trichoderma can attack them chemically. It does this by producing chemicals that are toxic to the fungi. Some of these compounds are volatile and travel through the air.

The chitinases and antibiotics work synergistically, affecting the target fungus more strongly than the production of either of them alone.


The soil is a fiercely competitive place and microbes usually die of starvation. Trichoderma is extremely adept at absorbing nutrients from the soil compared to other organisms.

It can obtain energy from complex compounds, such as chitin from fungi or cellulose from plants, which are difficult for other organisms to break down.

A compound that is typically scarce in soil is iron. Some strains of Trichoderma produce specialized compounds called siderophores that bind with iron and make it inaccessible to other fungi, completely inhibiting their growth.

Resistance to pesticides

Many strains of Trichoderma are unusually resistant to toxic compounds ranging from pesticides to chemicals produced by plants. Pesticide resistance includes herbicides, fungicides and insecticides such as DDT.

This gives an advantage to using these fungi to control pathogens, because you can alternate the application of strain T-22 with fungicides such as benomyl or captan.

How to use Trichoderma in your garden

If you apply this fungus to seed, it will colonize the root system of the plant as it grows. You can apply it directly in the furrow when planting. If you are planting sod, you can mix the fungus into the surface of the soil.

RootShield® Home & Garden with Trichoderma harzianum T-22

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For greenhouse or nursery planting, mix with your potting soil. Apply directly into the planting hole when transplanting trees or shrubs.

Strain T-22 prefers warmer weather, so you should apply it when the temperature is above 55°F.

Trichoderma is a widespread fungus with no history of toxicity to humans or when tested on laboratory rats. However, to be on the safe side and to prevent allergies from developing, use a dust/mist filter respirator when handling large quantities. The powder can cause eye irritation, so wear safety goggles.

For home growers, we recommend RootShield® Home & Garden (as shown above) through Arbico Organics.

Larger quantities and products with different application methods for commercial agricultural use are also available.

Store in the refrigerator in the original packaging until ready for us. You can also keep it above 75°F for short periods without any loss of performance.

The global biocontrol fungus

Trichoderma species are found in most soil types around the world and control other soil fungi using a variety of mechanisms. These range from direct parasitism to the production of antibiotics.

Fifteen years of research at Cornell University yielded the powerhouse Trichoderma harzianum strain T-22, which can be used on a huge range of crops.

Strain T-22 can also improve the nutritional status of crops in addition to controlling pathogens.

This broad biological control agent was one of the first biofungicides on the market and remains a very efficient fungus to add to your arsenal.

Have you used Trichoderma in the garden? If so, let us know how it worked for you.

And read on to learn more about biological control agents such as:

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