September 2025 - The Basics of Biocontrols in Propogation
Apr 01, 2026
Propagation Basics: Biocontrols Where Problems Begin
Fungus gnats and root diseases are ongoing concerns for anyone producing baby plants, especially during propagation when conditions are wet and root systems are still developing. In this edition of Koppert Corner, published through GrowerTalks, we focused on the biological tools that are most effective when applied early and correctly during propagation.
Fungus gnats are particularly damaging at this stage because young plants are actively producing new roots. While established plants with dense root systems can tolerate some feeding, propagules cannot. Under wet conditions, larvae can consume newly formed roots almost as quickly as the plant produces them, a challenge many propagators encounter early on.
Why Fungus Gnats Are So Damaging in Propagation
In this month’s Koppert Corner, we highlighted that fungus gnats cause the greatest impact when roots are young and actively growing.
Because propagation environments remain consistently moist for the first one to three weeks, they provide ideal conditions for larval activity. Feeding damage during this period slows root establishment and can stall crop progress before plants ever leave propagation.
Unlike later stages of production, there is very little margin for error early on. Damage that might go unnoticed in a fully rooted pot can have significant consequences in trays or URCs.
Nematodes Remain a Strong Foundation
To address fungus gnat pressure, we emphasized that a well-executed nematode program is hard to beat in propagation.
When applications are made consistently on a five- to seven-day interval, nematodes keep larvae thoroughly suppressed beneath damage thresholds instead of reacting after populations build. Standard industry rates are based on tray surface area, with 50 million nematodes applied per 1,000 sq. ft.
Placement is critical to success. Nematodes should remain concentrated in the top portion of the media where fungus gnat larvae are feeding, rather than being diluted deep into cells or trays.
Species selection also matters. Steinernema feltiae, sold as Entonem, performs well in cooler soil temperatures and is commonly used early in the season. Once soil temperatures reach or exceed 85F during summer, Steinernema carpocapsae, sold as Capsanem, becomes the preferred option. Capsanem also provides a broader target list and can be used exclusively year-round when shore fly pressure is a concern.
Root Pathogen Prevention Starts Early
Fungus gnats are only one side of the propagation equation. Root pathogen prevention is equally important, and we stressed the value of establishing beneficial microorganisms early.
Trichoderma harzianum T-22, sold as Trianum, is most effective when applied as early as possible because it colonizes and grows with developing roots. The wettable powder formulation mixes easily and can be tank-mixed with nematode drenches, making it a practical addition to early propagation programs.
Timing matters, however. Trichoderma establishes more slowly than bacterial biologicals, which is why we recommend letting it colonize first before introducing faster-moving organisms.
Why Biological Ordering Matters
In this Koppert Corner, we also addressed how different biologicals behave once introduced into the root zone.
Bacillus-based products are excellent complements to Trichoderma, but when they are applied at the same time, bacillus organisms tend to dominate. To illustrate this difference, we compared Trichoderma to a tank and bacillus products to fighter jets. Trichoderma moves slowly but creates a stable foundation, while bacillus organisms act quickly and aggressively.
Allowing Trichoderma to establish first gives it the opportunity to set up shop before bacillus products are introduced. Bacillus applications can then follow as plants move out of the wettest propagation phases, typically through regular spray-to-drip foliar applications.
This sequencing provides the strongest possible biological foundation for the crop moving forward.
The Bottom Line
The take-home message from this Koppert Corner is that propagation problems are best addressed early and proactively.
A consistent nematode program, paired with early Trichoderma establishment and intentional biological layering, provides durable suppression of fungus gnats and root pathogens rather than short-term fixes. When these tools are applied correctly, young plants leave propagation with stronger roots and fewer setbacks later in production.
This article is based on the Koppert Corner published in GrowerTalks and adapted for NaturalEnemies.com. To check out the original article, click here: Power of Seed; Poinsettias During Short Days; Biocontrols in Prop
Want more quick takes from Koppert's Corner on Grower Talks?
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Pesticide Resistance Residues on Garden Mums - May 2025
Prevent Fungus Gnat Larvae - June 2025
Problematic Thrips on Poinsettas - July 2025
Preparing Perennials for Winter - October 2025
Just a dip won't do - November 2025
Gerbera and Hydrangea - December 2025
