Trichoderma – Successful use of beneficial fungi against pathogenic decay fungi in trees

Since the 1920s, strains of various Trichoderma species have been used in agriculture worldwide as biological pest control. Of the currently known 33 Trichoderma species, T. harzianum and T. atroviride are more typically used in plant production, on lawns, ornamental plants and in tree nurseries.

From the extensive research work of Prof. Francis Schwarze (St. Gallen, Switzerland), it is now also possible to use certain Trichoderma harzianum strains against pathogenic decay fungi on trees. For this purpose, highly competitive strains were first tested. These then underwent a special “screening”, through which they were screened for competitiveness against individual cases of harmful fungi. Through this procedure, the naturally existing mycoparasitism of Trichoderma can be used specifically against harmful fungi.

Picture: A: Dense, white mycelia with brown crust of the Artist’s bracket (G. australe: syn: G. adspersum) on the control samples. B: Control samples of the flat artist’s bracket (G. lipsiense) C: Brittle cinder (Kretzschmaria deusta) formed a dense mycelium melanized crust on the samples (control). D: Trichoderma atroviride prevented colonization of the wood by the (G. australe). E: Trichoderma atrobrunneum/polysporum was able to prevent colonization by the G. lipsiense F: The samples treated with Trichoderma atroviride did not show any mycelial growth on K. deusta.

Mode of action: mycoparasitism

During mycoparasitism, Trichoderma grows towards wood decay fungi. The fast-growing hyphae wrap themselves around host fungal threads (=hyphae), attach themselves, then excrete enzymes to dissolve the enemy cell walls and feed on their cell contents.

Figure: Penetration into the mycelium of Inonotus hispidus (P) by hyphae of Trichoderma (T).

Further modes of action are:

The high competitive power of the mould through very rapid growth and efficient use of food sources.

Preimmunization through so-called “induced systemic resistance”, is induced by the plant during root contact with Trichoderma, and are messenger substances that spread throughout the plant.  Preimmunization (increased concentration of messenger substances) ensures that the plant is able to react quickly to a pathogen, as the messenger substances that trigger the production of defence substances are already present. This enables the plant to react more quickly to a pest or pest attack. The defence substances are produced throughout the entire plant body (=systemic resistance) as soon as the pest or pathogen occurs (=induced resistance).

The stimulation of root growth and the support of nutrient uptake results in plants having  an increased stress tolerance against potential pathogens.

Application of Trichoderma is a kind of cure over a longer time period

Trichoderma can be used in the form of a “cure” against some of the best known decay fungi (e.g. Artist’s bracket, honey fungus, giant polypore, brittle cinder fungus). Over four years Trichoderma is screened for competitiveness against the host pathogen should be applied four times in the vegetation period. For this purpose, a special gel (in which the spores “rest”) is dissolved in water and when activated is then distributed over the root space. Also, an intensive application of the gel can be directly applied to the exposed fruiting bodies.

However, the basic principle for this application is that the treatment is not started without a prior examination of traffic safety. For this purpose, a tensile test may be necessary in advance to check the still existing stability of the tree, e.g. if a beech is colonized by Ganaderma (or honey fungus). When using the product against the brittle cinder fungus, an expert accompaniment is generally recommended, because the spread of this fungus can be difficult to detect in roots and the stem base (sometimes high up at branch junctions) after the first visible occurrence.

Wound treatment with Trichoderma to prevent infections with harmful fungi

Trichoderma gel can also be applied to pruning wounds as a protective treatment; this makes it possible (even in the case of direct artificial inoculation of decay causing pathogens) to considerably reduce the potential for colonization.

Brushing Trichoderma-Gel onto the pruning wound surface

Picture: Significant reduction in the colonization of cut wounds by three decay fungi

Negative ecological effects are not to be expected from Trichoderma applications. Trichoderma is a beneficial fungus found (almost) everywhere in the soil and bark surface. Even with a high dosage, there are no negative effects on mycorrhizal fungi or root nodules (Vogel, 2017). In many cases, a promising treatment can be to combine Trichoderma with mycorrhizal symbionts (see chapter 7.5).