Start clean, stay clean

It’s not a secret — healthy plugs and liners are the foundation of growing a successful crop. Any pest, disease or cultural problem that originates in propagation will plague the entire crop.

How can you ensure problem-free propagation? The warm, humid environment needed for rooting or germination also promotes certain diseases and pests, making their management a constant struggle. In this article, I will provide some pointers on how to prevent and manage pests and diseases in propagation to produce the highest quality plugs and liners.

First, start clean. A high-quality propagation facility is one with the cleanest materials and environment. You should source cuttings from pest-, disease- or defect-free stock plants and seeds from certified, reputable producers. It’s nearly impossible to turn poor-quality, pest-ridden or disease-infected materials into high-quality plants. It’s better to discard or return subpar materials rather than attempt to salvage or “cure” them. You’ll have a hard time getting rid of a problem once it is introduced into your propagation or growing areas via “trash.” It is often worth the effort of identifying the origins of the “trash” and stop ordering from these sources.

Not all problems come from external sources — some persist from previous crops. Sanitation is the first and most important step in preventing the spread of pests and diseases from previous crops. Before bringing any new materials into your propagation area, thoroughly clean and sanitize benches and irrigation systems using an acidic stripper, followed by hydrogen peroxide or quaternary ammonium. Remove old trays, used media, plant debris, dead plants and weeds, all of which can serve as reservoirs for pests and diseases.

Use clean trays, new media and treated water. You need to properly clean and sanitize trays before reusing them. If you draw water from a pond, consider treating the pond with Cutrine® Plus, which not only cleans up algae but also oomycete (such as Pythium and Phytophthora) spores in the water.

Observe for potential problems as soon as you open the box. Carefully inspect cuttings for signs of poor handling, damage or infestation. No subpar material should be accepted or used. Cuttings should be stored in cool, moist (but not wet) conditions if they cannot be stuck immediately. These storage conditions will help minimize stress and prevent diseases.

Identify the problem you have observed, because selecting the most effective management approaches depends entirely on proper identification. Many diseases — including botrytis or gray mold, downy mildew, rhizoctonia root rot and bacterial leaf spots — can be introduced via cuttings and seeds. The warm, humid environment will allow gray mold and many root and stem rot diseases to break out quickly. Spider mites, broad mites, thrips and whiteflies often sneak in via cuttings. Fungus gnats and shore flies can quickly raise their ugly heads after the cuttings have been stuck.

The initial symptoms of pest infestation or disease infection often resemble symptoms of environmental stress or nutritional deficiency. Learn to distinguish these symptoms so you can quickly respond with proper management. Seek help from your extension specialists or preferred diagnostic services to properly identify these problems.

Consider a pre-planting dip before sticking to clean up suspected or light pest infestation on cuttings and young plants, such as those by spider mites, thrips and whiteflies. Studies demonstrated that dipping cuttings and plugs in 0.1-0.5% horticultural oil, 0.5% insecticidal soap + Beauveria bassiana (use powder formulation) or hexythiazox solution can reduce pest populations, which consequently will delay pest outbreaks and give biological control a better chance of succeeding. The risk of disease transmission, such as soft rot in poinsettias through dip solutions, is minimal.

You can modify the propagation environment to prevent or minimize disease outbreak. Clean, screened or isolated (from the other growing areas) propagation houses have fewer pest problems. Moisture management is the most important process that can limit disease outbreak and spread. Strategies that reduce excessive moisture — such as increasing temperature, light level, air circulation and water drainage, as well as reducing water frequency and splash — help create drier, less disease-prone conditions.

You can also minimize disease problems by speeding up rooting so that propagated materials are moved out of the wet or rooting phase quickly. Obtego® contains two beneficial species: Trichoderma asperellum and Trichoderma gamsii. Obtego is a biofungicide that parasitizes and outcompetes many soil-borne pathogens, such as Pythium, Phytophthora, Rhizoctonia and Berkeleyomyces (formerly Thielaviopsis). Obtego is also a biostimulant that promotes and speeds up callusing and rooting of cuttings, further denying entry to pathogens. A recent Plant Health Secrets article — bit.ly/obtego-fungicide — explains how Obtego benefits propagation and finishing a crop.

Scout regularly once cuttings are stuck and seeds are sown. For species that are notorious for certain pests and diseases, applying preventive insecticide or fungicide treatments (such as Obtego) immediately after sticking or sowing can be one of the most cost-effective and efficacious strategies.

Apply effective pesticides once pests and diseases are found. Biopesticides — such as Obtego for root rot diseases, Bacillus species for foliar diseases, entomopathogenic fungi for foliar insects and beneficial nematodes for fungus gnat control — are particularly well-suited for the early rooting phase. The moist rooting environment ensures high efficacy by these biological products. They also pose minimal risk to callus formation. Many other products can be used once cuttings callus. For example, drenching or sprenching media with Ornazin® (azadirachtin) is a great way to reduce fungus gnat and shore fly larval populations. Sprenching or spraying Ornazin also reduces mite and insect infestations on leaves. Camelot® O (copper octanoate) is an effective product for many foliar diseases, such as gray mold, bacterial diseases, anthracnose and downy mildew, and does not leave behind phytotoxic or objectionable residue on the leaf surfaces. Decree® (fenhexamid) is a preventive and curative product for combating gray mold in propagation and finishing.

As rooted cuttings and plugs move into the drier bulking-up phase, additional pest management tools become available. Predatory mites and macro-biological controls can be introduced, and systemic or translaminar insecticides are absorbed more efficiently. While pest control strategies in this phase mirror those used in finishing, maintaining clean liners and plugs is crucial for starting the finishing phase on the right foot.

Pest and disease management in propagation is not easy, but success in propagation is the cornerstone of successful finishing. By following these practical steps — starting clean, modifying the environment, scouting regularly and applying preventive and curative treatments as needed — you can produce healthy, high-quality liners and plugs, while setting the stage for a strong finish.

JC Chong, Ph.D., is the technical development manager for ornamentals at SePRO Corporation. sepro.com