Trichoderma biofungicides: how they work, where they fit and what affects performance

Trichoderma is a genus of filamentous fungi isolated from soil, decaying wood and plant organic matter, and several species are sold as biological fungicides [1]. The genus is a dominant part of many soil fungal communities and is known for its ability to colonise plant roots [2]. Reviews describe it as mainly used against soilborne diseases, with some use against leaf and panicle diseases [3]. FRAC, the Fungicide Resistance Action Committee, places Trichoderma strains in Group BM02, microbial biologicals with multiple modes of action, and records resistance as not known [4]. This article explains how Trichoderma works, which diseases the evidence supports, which conditions change performance, and how to read the viable count on a label.

1. What Trichoderma is and how it is classified

Commercial products use species such as T. harzianum, T. virens, T. asperellum and T. gamsii. Dormant spores are applied; they germinate, and the mycelium grows around the roots and forms a barrier to infection [1]. Trichoderma also stimulates root growth, which gives the fungus more root surface to colonise [1].

Names are changing. In its 2026 Code List, FRAC lists strain T-22 under Trichoderma afroharzianum and records a nomenclature change from Trichoderma harzianum [4], while extension tables published in 2024 still list T-22 under T. harzianum [1]. Expect both names in technical files and registration documents.

2. Four modes of action

FRAC lists the effects described for microbial biologicals as competition, mycoparasitism, antibiosis, membrane disruption by lipopeptides, lytic enzymes and induced plant defence, noting that not every effect applies to every group [4]. For Trichoderma, reviews name mycoparasitism, competition and antibiosis as the main direct strategies, alongside indirect effects through improved plant growth and stress tolerance [5].

Work at Cornell on strain T-22 shows mycoparasitism in practice. Trichoderma secretes an enzyme that dissolves the cell walls of other fungi, then enters and consumes them, and T-22 secretes more of the key enzyme, endochitinase, than wild strains [9].

3. Root colonisation decides the result

The most successful biocontrol strains show rhizosphere competence, the ability to colonise and grow in association with roots, and can colonise entire root surfaces for several months [6]. Colonisation of the root epidermis and cortex is linked to the production of plant cell wall degrading enzymes [2].

Most microbes introduced to fields fail because the native soil microflora has the competitive advantage; T-22 was bred for the rarer ability to colonise roots under field conditions [9]. In Cornell trials, T-22 grew on the root surface and lived mostly on compounds secreted by the root. Because it multiplies, a small inoculum spread with the roots and protected the whole root system through the season, whereas seed applied chemicals protect only the seed, for a few weeks at most [9]. The yield response was seen mainly when plants were weakened or stressed, not in crops already growing at their potential [9].

4. Target diseases supported by reviews and extension

Trichoderma is mainly used against soilborne diseases, and greenhouse use centres on root and crown diseases; reviews also report some use against leaf and panicle diseases [3][6].

These are findings from research and extension programmes, not a list of registered uses. The label registered in each country sets the crops, targets and rates.

5. Conditions that affect performance

Temperature

In culture, Trichoderma grows slowly below about 16 °C (60 °F). In sweet corn, T-22 colonised roots well at 16 °C or above, colonisation was lower than desired with soil at 13 °C (55 °F) at sowing, and at 10 °C (50 °F) neither the crop nor the fungus established well. Early sown crops and overwintering crops are therefore likely to give unsatisfactory colonisation [9]. Optimum temperatures differ by species and isolate: about 30 °C for T. harzianum [8], and 24.6 to 29.4 °C for three isolates taken from commercial products in a Brazilian study [10].

Soil moisture, aeration and pH

T-22 did not work in flooded or crusted fields, because roots and fungus both need air to grow. Extremely well drained soils are the most difficult for wild Trichoderma, although T-22 populations there were still high enough to be effective, and roots in soils high in calcium were better colonised [9]. In a Brazilian study, isolates taken from commercial products tolerated pH 5 to 9 [10]. For spray applications, formulation carriers are chosen partly to protect conidia against UV radiation and washout [11].

Timing

Biological fungicides are preventive. They will not cure diseased plants, must be in place before infection when used on foliage, and need reapplication to protect new growth [1][6]. They also work best alongside sanitation and clean planting material [1].

Chemical fungicides

Trichoderma species are relatively tolerant of toxins produced by soil microbes, plant antimicrobial compounds and even some chemical fungicides [6], and a Chinese review notes that this tolerance allows combined programmes [12]. Tolerance is not universal. In a Brazilian laboratory study, 16 of 32 agricultural inputs inhibited mycelial growth of T. afroharzianum by more than 67%, although 12 of those 16 did not reduce conidial germination in a simulated spray solution; picoxystrobin plus benzovindiflupyr and a Bacillus based bionematicide sharply reduced germination, and mixtures of picoxystrobin plus prothioconazole and trifloxystrobin plus tebuconazole affected strains differently [13]. In another study, azoxystrobin plus difenoconazole and boscalid reduced growth of three isolates by up to 50% [10]. The Brazilian authors call for field validation of these results [13]. Check the manufacturer's compatibility information before mixing, and apply immediately after mixing with water [1]. In Cornell work, applying T-22 to seed in the planter box let the fungus largely escape long term exposure to seed applied fungicides [9].

6. How viable content is expressed

The content of a Trichoderma product is the number of living propagules it carries, usually given as colony forming units (CFU) per gram, and sometimes as conidia or spores per gram. Concentrations in biocontrol products typically range from 1 × 10⁵ to 1 × 10⁹ CFU per gram [11]. When comparing offers, read the unit, the guaranteed minimum and the expiry date together, since viability falls during processing and storage [1][11].

Triva™, supplied by Huasheng, is a Trichoderma harzianum T-22 wettable powder declared at no less than 3 × 10⁸ CFU/g.

7. Storage and shelf life

Because biofungicides are living organisms, they have a limited shelf life and need proper storage. Do not stockpile them, watch the expiry date, and store most products under cool, dry conditions [1]. Dry formulations prolong shelf life and avoid the need for low storage temperatures, whereas liquid and gel formulations, with higher water activity, are harder to stabilise because conidia may germinate in the pack [11]. Listed shelf lives of Trichoderma products on the European market show the effect of temperature: one wettable powder lists two years at 4 °C but six months at 15 to 20 °C [11]. Conidia kept in plain water lose viability through imbibition damage [11], and extension advice is to apply immediately after mixing [1].

8. Fitting Trichoderma into a disease programme

FRAC regards microbial biologicals in BM01 and BM02 as low or very low resistance risk. They can be used alone or in mixtures, with no limits on number, timing or sequence of applications beyond the label and local regulations [14]. Extension services also list rotation with conventional fungicides as a way to reduce the risk of resistance to single site products [1].

• Apply before disease appears, in the growing medium, at sowing or at transplanting, so that roots are colonised from the start [6].
• Match timing to soil temperature; cold soils slow colonisation [9].
• Avoid flooded or crusted soil, where T-22 did not work because roots and fungus both need air [9].
• Check compatibility data before mixing with fungicides or other inputs [1][13].
• Keep sanitation, clean planting material and other cultural measures in place [1].
• Store cool and dry, and use within the expiry date [1].
• Leave some plants untreated as a check when testing a product on your own farm [1].

Frequently asked questions