Introduction
Organic farming is the way of producing good quality farm products in harmony with nature. Organic farmers optimise the growing conditions of crops by enhancing the natural fertility of the soil to ensure good nutrient and water supply, creating diverse cropping systems, and promoting natural enemies of pests, recycling organic materials and manures, and using natural inputs while renouncing synthetic chemical pesticides and fertilisers.
The organic approach to plant pest and disease management makes reference to the four principles of organic agriculture: the principle of health, the principle of ecology, the principle of fairness, and the principle of care (see IFOAM principles of organic agriculture). Generally, organic farmers aim at sustaining and enhancing the health of their soils, plants, animals, humankind and—in the broad sense—the planet. The health of individuals and communities cannot be separated from the health of ecosystems. Therefore, by encouraging healthy and fertile soils, establishing diversified natural cropping systems and maintaining a diverse natural environment, farmers can produce healthy crops that foster the health of animals and people.
Healthy plants resist and tolerate physiological disruption and damage from disease-causing organisms and pests better. Thus, organic farmers aim at optimising the growing conditions for their crops to make them strong and resilient. At the same time, they encourage natural control mechanisms like the promotion of beneficial organisms to limit the spread of pests and diseases. Doing so, organic farmers give priority to preventive measures instead of relying on direct control measures only. Direct control measures are only applied when the pests and disease pathogens threaten to cause major losses.
The three-step approach
Organic pest, and disease management can be seen as a three-step approach with multiple tools.
Step 1: Consists of providing good growing conditions for plants to enhance their resilience and resistance and hence withstand pest and disease attacks better.
Step 2: Consists of encouraging natural control mechanisms through promotion of natural enemies, ensuring good crop hygiene, and monitoring pests and diseases populations for timely action.
Step 3: Involves application of direct control measures to kill the pests or disease-causing organisms when they reach critical levels in a way that has minimum residual effect to the ecosystem.
Each step of the three-step approach builds the foundation for the next step.
The aim is to optimise steps 1 and 2 to encourage natural self-control of pathogens and to minimise the direct control measures in step 3. With proper and efficient application of steps 1 and 2, direct intervention is usually not needed. This saves on costs and prevents negative impacts of some direct control measures on the environment.
Decades of practical experiences from organic farmers and results of scientific research on organic pest and disease management in the last 30 years have shown that the combination of indirect and direct control measures is most effective. As knowledge of the interaction of pest and disease pathogens and their natural enemies increases further, efficiency of this holistic approach also increases. Ideally, farmers will eventually be able to abandon any direct control measures and instead maximise the use of natural processes.
In comparison, the three-step approach also applies to human health care management:
1st step measures: Provision of sufficient and healthy food and water, and the preservation of a healthy environment to encourage human health. It also includes good behavioural practices to avoid illness by simple measures of hygiene (e.g. washing hands regularly and brushing teeth), appropriate exercise to strengthen the body and refraining from risky conditions or situations.
2nd step measures: Preventive intake of vitamins when necessary, antioxidants or probiotic agents and the use of natural medicine against illness (e.g. traditional medicine, medical herbs and homeopathy).
3rd step measures: Direct treatment using antibiotics and other medicines to kill off infections.
Step 1 strategies and tools
These strategies and tools aim at providing good growing conditions to enhance plant health and prevention of introduction and spread of pests and diseases. This can be achieved through the following practices:
Choice of appropriate crop varieties suitable for the location. Where possible, varieties tolerant or resistant to pests and diseases should be used.
> Using disease- and pest-free planting materials.
> Soil fertility improvement to encourage strong and vigorous growing plants by using compost, animal manure, green manure, and other natural nutrient sources.
> Intercropping and crop rotation to reduce the multiplication rate of pests and disease-causing organisms.
> Other good management practices to ensure proper growth such as timely planting, proper spacing, water conservation, pruning, shade management and timely harvesting.
Step 2 strategies and tools
These strategies and tools aim at enhancing the proliferation of a variety of organisms (including natural enemies) around and within the crop fields. These include:
Planting hedges of indigenous plant species around fields to attract natural enemies. Allowing flowering plant species to grow within crops to provide nectar and pollen for natural enemies like ladybird beetles, hoverflies, and parasitoids.
Trap cropping to attract pests to non-crops or repel/push away pests from the crops (e. g. the push-pull strategy).
Field hygiene, including timely weeding to remove alternative hosts, rogueing infected plants and plant parts, proper disposal of infected plants and cleaning or disinfecting tools used on infected plants/fields.
Step 3 strategies and tools
In situations of heavy infestations or very devastating pests and diseases, direct measures will be needed to minimise losses.
These include:
Biological control agents such as predatory insects and mites, insect parasitoids, viruses and bacteria (e. g. Bacillus thuringiensis Bt).
Approved commercial or self-made insecticides or acaricides (against mites) of biological or mineral origin including plant extracts, plant oils, mineral oil, copper, and sulphur.
If available, insect pheromone traps may be used to disrupt mating of pests.
Light, bait or colour traps may be used for mass-trapping pests.
Hot water treatments of seeds to limit seed-borne diseases.
These tools will only be fully effective when tools in the other two steps are applied properly.