Plant Propagation

Clean-plant overview

A “clean plant” used to mean simply that pests and diseases could not be detected. Another meaning is now being added to the phrase: a “clean plant” can be produced and protected without pesticide residues. That definition is gaining ground fast among finished-plant growers.

Increasingly, growers of finished plants are requesting young plants that have been protected with biological control agents as the primary means of defense. These growers have learned first-hand the many benefits of biocontrol, and receiving residue-free plants allows their own pest-control program to function without disruption.

Strategy

Seedlings and unrooted cuttings are very susceptible to pests and diseases. As a result, propagators use a pro-active approach with biocontrol agents. Instead of trying to establish a population of predators and parasites, they run mass-releases periodically to eliminate the first pests and stop them dead in their tracks.

The choice of biocontrol agent depends on the growing system. Plants rooted under mist or plastic — and trays germinated in growth chambers — are treated with pest-killing nematodes first, then inoculated with the regular BCA program (see release-rate table) after moisture is reduced. Growing systems that don’t use a lot of moisture should be inoculated with regular BCAs right away.

The propagation phase of a plant’s life is short, and this guide is specific to that phase. It is not a stand-alone program. It is critical that the recipient of the “clean” plant initiate their own pest-control program immediately on arrival.

Propagation biocontrol is not a stand-alone program. The receiving grower must launch their own pest-control plan the moment plants arrive.

Major pests & biocontrol agents

Fungus gnat

Release the predatory soil mite Stratiolaelaps scimitus (formerly Hypoaspis miles) preventively onto newly sown or newly planted/transplanted pots and plug trays. Apply to all “dry” crops, or after a crop has finished its “wet” phase. Usually one application is all that is needed.

For “wet” growing systems, apply the nematode Steinernema feltiae and then place plants under mist or plastic. Nematodes can also be applied during and after this phase — check with a Beneficial Insectary representative for the timing best suited to your system.

Shore fly

Dalotia coriaria (formerly Atheta coriaria) is a rove beetle that devours all immature stages of shore fly. Apply to all “dry” crops, or after the crop has finished its “wet” phase. Usually one application is all that is needed.

For “wet” growing systems, apply the nematode Steinernema carpocapsae and then place plants under mist or plastic. As with fungus gnat, nematodes can be applied during and after this phase too.

Thrips

For all “dry” crops, release Neoseiulus cucumeris preventively. Release Orius insidiosus on hot spots. For “wet” crops, apply Steinernema feltiae to interrupt the soil-stage pupation that drives WFT cycling.

Spider mite

For all “dry” crops, release Phytoseiulus persimilis on detection of spider mite. Apply to hot spots or, where pressure is widespread, run a blanket treatment across the crop.

Whitefly

For all “dry” crops, apply the parasitic wasps Encarsia formosa and/or Eretmocerus eremicus. These parasites attack the young stages of whitefly, not the adults — so weekly releases are the standard cadence to keep the population pinned.

Aphid

For all “dry” crops, make preventive releases of multiple aphid parasites weekly. The parasite-mix products are designed for situations where the species of aphid is unknown. Release Chrysoperla rufilabris (green lacewing) on hot spots for fast knockdown.

Why clean plants matter

A clean-plant program isn’t just a propagator’s sales argument — it sets up the entire downstream IPM program. Finished-plant growers running biocontrol can’t tolerate residues that knock out their beneficials. Propagation that runs on BCAs from the start delivers material that plugs straight into a downstream biocontrol program, and pest hot spots show up later, smaller, and easier to manage.

Clean plants now means residue-free as well as pest-free. The finished-plant grower’s biocontrol program depends on it.

Release rate guidance

The rates below are the standard propagation guide for biocontrol releases. Apply to newly planted or transplanted material on dry crops; switch to nematode treatments for crops still in the wet phase under mist or plastic.

Note: the above is intended as a guideline and is not a written recommendation. Contact a Beneficial Insectary representative for crop-specific advice.