Skip to content

Trichoderma

Also known as Trichoderma harzianum, T-22

Beneficial or harmlessBeneficial
Trichoderma harzianumPublic domain

In short

Trichoderma is a group of fungi found in almost all soils. Selected strains, such as Trichoderma harzianum T-22, are sold as biological fungicides that colonise roots and attack root-rot fungi such as Pythium, Rhizoctonia and Fusarium. They protect before disease starts; they do not cure it.

How it looks

In culture or on decaying material, fast-growing colonies that start white and soon form green or yellow-green tufts of spores. In a plant pot it is usually invisible. A green mould appearing on mushroom-growing substrate is often a Trichoderma species.

Signs

No damage to plants. Treated plants may show less damping-off and root rot and sometimes faster root growth.

What favours it

Warm soil or mix (about 16 °C and above for T-22 colonisation) with good aeration; it performs poorly in waterlogged or crusted media.

Prevention

  • Apply at sowing or potting so the fungus colonises new roots before pathogens do.
  • Keep media well aerated; Trichoderma cannot compensate for waterlogging.

Treatment

Start with the first step and move down only if the problem persists.

  1. Use as a seed treatment, drench or mix amendment according to the product label.
  2. Combine with good drainage and hygiene rather than relying on it to save plants that are already rotting.
  3. Check compatibility with any fungicide before using both.

Pros and cons

Pros

  • Parasitises and competes with major root-rot and damping-off fungi.
  • Can help roots grow faster and cope with some physical stresses.
  • Common, naturally occurring soil fungus.

Cons

  • Preventive only; will not rescue roots that are already rotted.
  • Ineffective in waterlogged or poorly aerated mix.
  • Some species cause green mould in mushroom cultivation, so keep products away from mushroom growing.

Look-alikes

Mycorrhizal fungi
Form a nutrient-trading partnership inside roots rather than attacking other fungi.

Where you find it

Vegetable seeds and transplants, greenhouse and container crops prone to damping-off and root rot.

Sources

  1. Trichoderma — Wikipedia
  2. Trichoderma for Control of Soil Pathogens — UConn IPM

Written in our own words from these sources. Check a product label before using any treatment.