Beneficial organisms in the organic garden

It is surprising to learn how many dedicated gardeners have limited understanding of the variety and characteristics of beneficial organisms which can be applied to control destructive insect pests. This may be partly due to the amount of research and funding which is derived within the tradition of Integrated Pest Management (IPM). Organic growers tend to distance themselves from any approach which includes the application of chemical controls. While IPM advocates the controlled use of chemical insecticides, it is possible to concentrate on the biological controls and other strategies which are harmonious with our basic organic principles. To ignore the positive aspects of IPM seems overly restrictive.

Beneficial organisms are generally classified into three general groups: predators, parasites, and pathogenic organisms. Predators are selected for their capacity to feed directly on nuisance insect species. An example of a predator is the lacewing which feeds upon aphids and small caterpillars which might otherwise damage and weaken vine crops like melons, grapes, passionfruit, and tomatoes. Parasites have complicated life cycles which involve depositing their eggs within a living insect host. An example of a parasite is the Trichogramma wasps which prevent the larval stage of cabbage and codling moths. Pathogens are essentially bacterial, fungal, or viral organisms which inhibit the lifecycle of nuisance insects. A widely used bacterium is Bacillus Thuringiensis (BT), which has the potential to control many types of leaf eating caterpillar.

Dependent on the garden and situation, beneficial organisms can be deliberately introduced or encouraged as part of the natural ecological balance. Most organic purists will choose the latter approach since it is most likely to achieve long-term benefits without disruption to the established ecology. This introduces one of the most important paradoxes of organic stewardship. In order to encourage beneficial insects, the garden must contain a sufficient population of the pest species. The two groups must be balanced to facilitate the ongoing control of nuisance insects within a reasonable level.

There are limited numbers of beneficial organisms which can be directly purchased from agricultural and horticultural suppliers. In most cases the organisms are mass reared under controlled conditions, and must be released within a relatively short time period. The deliberate introduction of beneficial organisms is an operation which typically requires a considerable degree of planning and coordination with other garden activities. This is particularly true for the organic environment where adaptation is a component of the survival and growth strategy for all species.

Biological controls can also, and in most cases should, be accompanied by the types of cultural control which coincide with the basic principles of organic gardening. Cultural controls are specific environmental interventions which deter nuisance insects or improve the local conditions which support natural predators and parasites.