Strategies for Prevention and Control of Common Pests and Diseases

Overview

Managing pests and diseases in agricultural and horticultural systems requires a multi-faceted approach. Prevention is always preferable to cure — stopping a pest or disease establishing is far more cost-effective than controlling an established problem. Control strategies are applied once a pest or disease is present and require careful selection to minimise economic loss while limiting environmental harm.

VCAA FOCUS: Students must understand the broad categories of pest and disease management strategies. The specific pests and diseases named in the study design (aphids, western flower thrips, intestinal worms, footrot, fungal rusts, milk fever) are covered in their own Key Knowledge entries — this KK introduces the general strategic framework.

The Difference Between Prevention and Control

Effective management programmes integrate both — prevention reduces the frequency of control interventions, and control is applied strategically when thresholds are exceeded.

General Categories of Prevention Strategies

1. Cultural and Agronomic Practices

Adjusting farming practices to make the environment less favourable for pests and diseases:

• Crop rotation — prevents build-up of soil-borne pathogens and pest populations (e.g., rotating brassicas reduces clubroot)
• Resistant varieties — planting cultivars bred for disease or pest resistance (e.g., rust-resistant wheat varieties)
• Sanitation — removing crop debris after harvest to eliminate overwintering sites for pests and pathogens
• Isolation/quarantine — keeping new plant material or animals in isolation before introducing them to the property
• Timing of planting — avoiding periods when pest populations are highest
• Optimal plant spacing — reduces humidity and improves airflow, limiting fungal disease spread

2. Biological Control (Preventive Use)

Maintaining populations of natural enemies (predators, parasitoids, pathogens) in the agricultural system to keep pest populations below damaging levels:

• Encouraging beneficial insects by reducing broad-spectrum insecticide use
• Habitat plantings (shelter belts, beetle banks) that provide refuges for predatory insects
• Conservation of natural predators on-farm

3. Physical and Mechanical Barriers

• Insect exclusion netting — prevents flying insect pests from reaching crops
• Fencing — prevents entry of pest animals (rabbits, foxes, kangaroos)
• Row covers — protect individual plant rows from insect damage
• Seed dressings — fungicide-treated seed prevents soil-borne diseases during establishment

4. Quarantine and Biosecurity Measures

• Farm biosecurity plans — protocols for visitors, vehicles, and equipment entering the property
• Importing clean planting material — certified disease-free seed and propagation material
• National and state border controls — prevent introduction of exotic pests and diseases

General Categories of Control Strategies

1. Chemical Control

The use of registered pesticides to kill or suppress pest and disease organisms:

• Insecticides — kill insect pests (e.g., synthetic pyrethroids, neonicotinoids, organophosphates)
• Fungicides — inhibit or kill fungi (e.g., triazoles, strobilurins, copper-based compounds)
• Herbicides — kill weeds (covered separately under weed management)
• Anthelmintics (drenches) — kill internal parasites in livestock (e.g., macrocyclic lactones, benzimidazoles)
• Acaricides — target mites and ticks

Important considerations:
- Always use registered products and follow label directions
- Observe withholding periods (WHP) before slaughter or harvest
- Rotate chemical classes to minimise resistance development
- Apply at correct timing to target the most vulnerable life stage

EXAM TIP: Chemical control is most effective when applied as part of an IPM strategy — not as the only tool. Over-reliance on chemicals drives resistance.

2. Biological Control

Using living organisms to suppress pest populations:

• Predators — ladybirds eat aphids; lacewings eat thrips; predatory mites eat spider mites
• Parasitoids — wasps (e.g., Trichogramma) lay eggs inside pest larvae
• Pathogens — entomopathogenic fungi (Beauveria bassiana) infect and kill insects; Bt (Bacillus thuringiensis) used against caterpillars
• Commercial releases — augmentative release of purchased beneficial insects into greenhouse crops

3. Physical and Mechanical Control

• Trapping (sticky traps, pheromone traps) — monitors and/or reduces pest populations
• Manual removal of diseased plant material
• High-pressure washing and hygiene protocols for equipment
• Flame weeding (for some weed and soil-borne disease situations)
• Removal and destruction of infected animals or plants (critical in notifiable disease outbreaks)

4. Nutritional and Management Control (Metabolic Conditions)

• Correct mineral supplementation (e.g., calcium boluses for milk fever prevention)
• Pre-calving nutrition management
• Avoiding rapid dietary changes in livestock
• Soil testing and fertiliser programmes to prevent plant nutrient deficiencies

5. Vaccination (Animal Diseases)

• Vaccines available for many viral and bacterial diseases (e.g., clostridial diseases in sheep, bovine respiratory disease in cattle)
• Prevents disease in vaccinated animals but does not treat existing infection

Decision-Making Framework: When to Apply Control

Control strategies are most effective when applied based on economic thresholds — the point at which the cost of control is less than the economic damage caused by the pest or disease.

Monitor → Identify → Assess population/severity →
Compare to threshold → Apply control if threshold exceeded

APPLICATION: A market gardener growing lettuce would not spray insecticide at the first sign of a single aphid. They would monitor aphid numbers, assess whether natural enemies are present, and only intervene chemically if populations exceed an economic threshold that justifies the cost and risk of spraying.

Summary

Prevention strategies — cultural practices, resistant varieties, biological approaches, quarantine measures, and physical barriers — reduce the likelihood and severity of pest and disease problems. Control strategies — chemical, biological, physical, and nutritional — are applied when prevention is insufficient. Selecting the right combination of strategies, based on the specific pest/disease, the crop/animal, and the production system, is the essence of integrated pest and disease management.