Pest Management and Biosecurity

A greenhouse or indoor farm removes the seasonal interruptions that limit pest populations outdoors. Temperature stays in the range that shortens insect generation times, humidity is often favourable, natural enemies are absent unless introduced, and the crop is a single species planted at high density. Under those conditions a small founding population can become a production problem in weeks.

The response that scales is structural. Exclusion, hygiene and monitoring are cheap, repeatable and effective against every pest at once, and they work before there is a population to fight. Reactive control is expensive, disruptive, constrained by law, and always applied to a population that is already established. The order of effort should follow that difference.

Direct feeding damage is often the smaller part of the loss. Several of the common protected-cultivation pests transmit plant viruses, and a virus introduced by a vector cannot be cured — infected plants are removed, and the crop plan absorbs the gap. A pest problem can therefore become a plant-health problem that no amount of subsequent control reverses.

There is also an operational cost that is easy to underestimate. Once a population is established, control activity competes with routine work for the same labour, restricts movement through the house, may impose re-entry and harvest intervals, and can conflict with any biological control programme already running. A single incursion reshapes the working week for a month.

Finally, repeated reactive intervention selects for resistance in the pest population. Every use of a mode of action removes the individuals susceptible to it, so the strategy that seems to work fastest is also the one that erodes its own future effectiveness. This is the strongest technical argument for putting prevention first.

Integrated pest management as a hierarchy

Integrated pest management is not a mixture of methods applied simultaneously. It is an ordered sequence in which each step is used only when the ones before it have been exhausted. The order reflects cost, reliability and consequence, and skipping to the end is what produces resistance, residues and repeat problems.

Prevention and reaction

Prevention is applied to the system, is scheduled, has a predictable cost and works against unknown future problems. Reaction is applied to a population, is unscheduled, has an unpredictable cost and works only against the problem already present. The two are not alternatives on equal footing. A farm that finds itself reacting frequently has a prevention defect, and treating the symptom repeatedly will not find it.

Action thresholds

Not every insect found requires a response. An action threshold is the population level at which the expected damage justifies the cost and disruption of intervening. Thresholds differ by pest, by crop, by growth stage, by whether the pest transmits a virus in that crop, and by the market's tolerance for damage on the harvested part. A threshold for a leaf pest on a fruiting crop is not a threshold for the same pest on a leafy crop where the leaf is the product.

Two technical relationships underlie most of the practical decisions: how fast a founding population grows, and what mesh is needed to exclude a given insect at an acceptable ventilation penalty.

The practical consequence is that scouting frequency is a design parameter. Weekly inspection in a warm house with a fast-breeding pest can allow several generations between detections; the same interval in cooler conditions may be entirely adequate.

The common pests of protected cultivation

Exclusion

Exclusion is the whole perimeter, not just the vents. Insect screening on ventilation openings is the visible element, but the practical failures are usually elsewhere: doors propped open during harvest, an unscreened extraction fan, a gap at a gutter or a floor edge, a torn cladding sheet, drains without traps, and vegetation growing against the outside of the structure acting as a staging post.

• Screen every opening through which air can enter, including fan intakes and evaporative cooling pads, and inspect screens for tears and blockage as a scheduled task.
• Use a double-door entry or an airlock where the structure and budget permit, and enforce single-door discipline where they do not.
• Keep a vegetation-free margin around the structure. Weeds outside are the reservoir from which the inside is colonised.
• Control the movement of tools, trolleys, crates and staff between zones, and work from the cleanest zone to the dirtiest rather than the reverse.
• Treat pallets, packaging and returned crates as entry routes, because they are.

Quarantine of incoming plant material

Incoming young plants are the single highest-risk entry route, because they carry pests directly into the middle of the crop, past every perimeter control. A quarantine area — physically separate, with its own tools and its own traps, inspected on a defined schedule before release — is the control. Plants should be inspected on arrival, held for long enough to allow eggs to hatch and a population to become detectable, and released only after that inspection.

Where a farm propagates its own material, the same discipline applies internally. Propagation should be the cleanest zone on the site and should never be entered after working in production without a change of clothing and hands.

Monitoring and scouting

Sticky traps give a continuous, comparable index of flying adult activity. Coloured traps are placed just above the canopy and raised as the crop grows, distributed on a grid with additional traps at doors, vents and other likely entry points. They are counted and recorded on a fixed day each week, and the number is written down even when it is zero — the value of trap data is entirely in the trend and the map.

Traps do not detect everything. Mites, immature stages and pests that do not fly are found only by looking at plants. Structured plant inspection means a defined number of plants, at defined positions, examined in a defined way — leaf undersides, growing points, flowers — rather than a general walk-through. Both methods are needed, and neither substitutes for the other.

Biological control

Biological control uses natural enemies of the pest: predators that consume it, parasitoids that develop inside it, and entomopathogenic organisms that infect it. It works best when introduced early, against a low and known population, and when the house environment suits the agent as well as the crop. Agents have their own temperature and humidity requirements, their own establishment times, and their own sensitivities to residues left by earlier chemical use.

1. Map the house and number the trap positions. A count without a location is half a data point.
2. Fix the scouting day and keep it, so the interval between counts is constant and the trend is interpretable.
3. Record zero counts. A run of zeros is what makes the first non-zero count meaningful.
4. Inspect leaf undersides, growing points and open flowers, since these are where several of the common pests are found first.
5. Mark and revisit any focus found, rather than relying on memory of roughly where it was.
6. Keep a reference sample or a clear photograph of anything unidentified, and obtain a proper identification before deciding anything.
7. Review the trap map monthly against the house layout. Repeated first detections at the same door or vent identify the exclusion defect.

Staff training carries much of this. The people who spend the most hours among the plants are the ones most likely to see the first damage, and a short, specific briefing on what to look for and whom to tell is worth more than an elaborate protocol nobody follows.

The structure determines how much pest management is possible. A house with generous screened vent area, sealed gutters, a functioning airlock, a separate quarantine bay and a hard, drainable floor can be run largely on exclusion. A house with none of those will need continual intervention regardless of how competent the grower is, and the shortfall cannot be closed by effort.

Climate control interacts directly with pest pressure. Persistent leaf wetness and stagnant air favour some organisms; hot dry conditions favour others. Adjusting climate for pest reasons has to be weighed against what the crop needs, and the trade-off is genuine rather than free.

• Spend on exclusion before spending on control. The perimeter is the only measure that works against pests not yet identified.
• Quarantine every incoming plant, without exception, including material from a trusted supplier.
• Monitor on a fixed schedule and record everything, including nil returns.
• Set action thresholds in advance, per pest and per crop stage, so a decision under pressure is a lookup.
• Identify before acting. Control chosen against a misidentified pest is cost without benefit.
• Follow local registration and label law for any chemical intervention, observe re-entry and harvest intervals, keep records, and make the decision with a qualified agronomist rather than alone.

• Write a biosecurity procedure covering entry, movement, tools, incoming material and waste, and make it short enough to be followed.
• Inspect screens, doors and seals on a maintenance schedule, not only when a pest appears.
• Clear the crop and the debris completely between cycles, and leave no bridging plants for the pest to survive on.
• Keep the quarantine area genuinely separate, with dedicated tools and its own traps.
• Plan the biological control programme before planting, with agent selection and timing agreed in advance.
• Rotate modes of action where any chemical use occurs, under agronomic advice and within label law, to slow resistance development.
• Debrief after every incursion and fix the step in the hierarchy that failed.

Advanced practice is largely about the integration between control methods rather than any single method. Compatibility is the hard part: an intervention that suppresses a pest and also removes an established natural enemy population can leave the crop worse off within a fortnight, because the pest usually recovers faster than its predator. Any decision to intervene in a house running biological control has to be assessed against the agents present.

Resistance management is the other structural discipline. Because a protected crop is a closed, uniform population under repeated selection, resistance develops faster there than outdoors. Rotating modes of action, limiting the number of consecutive applications and leaning on non-chemical steps are the standard responses, and all of them are planned across a season rather than decided in the moment.

Finally, pest management should be evaluated economically over the whole crop rather than per incident. The right comparison is between the annual cost of prevention — screening, quarantine space, scouting labour, biological control agents — and the annual cost of the losses, disruption and interventions that occur without it. On that basis prevention is usually the cheaper programme, which is the practical reason the hierarchy is ordered as it is.