Pests can cause extensive damage to crops. We need to work together to develop effective and sustainable pest control in agriculture using the principles of integrated pest management.
Potatoes New Zealand’s Paula Lleras and Dr Paul Horne, IPM Technologies Pty Ltd
When controlling pests, it is often assumed that pesticides are the only option but in fact there are three control methods. Using pesticides is one of those methods and the others are biological controls (usually insects and mites that eat the pests) and cultural controls (management methods that influence either pests or biological control agents). All Integrated Pest Management (IPM) means is trying to use all three methods in a compatible way. So, there are three control methods working on pests and there is not a reliance solely on pesticides.
Biological controls
The key biological controls are either Predators, Parasitoids or Pathogens. Depending on the pest involved, different biological control agents will provide different levels of impact on the pests. For example, aphids are attached by a range of predators (including ladybirds, lacewings and hoverflies) and parasitoids (tiny wasps) and pathogens (usually fungi) and potato tuber moth is attacked by native predatory damsel bugs and introduced species of parasitoid wasps. However, when a new pest (such as tomato potato psyllid (TPP)) arrives it often has escaped key parasitoids and so the generalist predators become relatively more important biological control agents.
Cultural Controls
Cultural controls are often the most important aspect of pest control but are often underestimated. For example, location (isolation) is a control method used by seed growers to reduce risk of virus spread by insects. Variety can be all that is needed at times, as a resistant variety means that no additional controls are required for that problem.
For potato tuber moth, soil management and irrigation are key aspects for control by stopping caterpillars obtaining access to tubers under the ground. If these control options are not utilised then biological controls and pesticides may not provide sufficient protection, especially for high-setting varieties. Reducing pest pressure by removing alternative hosts (eg boxthorn for TPP) or controlling volunteer potatoes and weeds for thrips management can significantly affect pest control.
The other way that cultural controls can work is by providing a nectar source for beneficial species such as wasps and hoverflies. This gives the biological control agents a food source that can significantly extend their life-span and fecundity (how many eggs they produce). In this way the impact of even a small population of beneficial species can be greatly enhanced. These beneficial species are active flyers and so border plantings are sufficient for a population of predators or parasitoids over an entire paddock.
Pesticides
Insecticides and fungicides vary greatly in terms of their impact on biological control agents. Some are toxic to many beneficial species but many newer pesticides can be safe to some species and highly toxic to others. Obviously, in an IPM strategy the aim would be to select a product that kills the pest but not the key beneficial species. To assist in making such a decision there are a range of websites, that are often free, which provide “side-effects guides”. These are frequently presented as colour-coded (“traffic light”) charts, with green being safe, yellow being moderately toxic and red being highly toxic to any particular species. In this way the relative impact of different pesticides can be compared and where some choices are available, a grower can choose a least toxic option.
It is important to recognise that these guides are constructed using a single spray at the label rate and so multiple sprays or the use of higher rates can significantly increase the side-effects. It is also important to realise that the three categories (safe/ moderate/ toxic) have a broad range within each case. Usually “Safe” is described as killing 0 – 29% of the test population and “Moderate” is defined as killing 30 – 79% of the test population. So even a couple of “safe” sprays can have a detrimental impact on beneficial insects and mites. The guides are simply providing the relative impact of products and it is still important to minimise pesticide use.
Integrated Pest Management (IPM)
When growers implement IPM the results can be remarkable. By avoiding disruptive insecticides and encouraging beneficial species, the impact of biological control agents becomes very significant. When combined with other cultural controls the overall pest management is achieved without reliance on pesticides alone. This has another benefit in that the reduced use of IPM compatible insecticides means that the likelihood of insecticide resistance is also reduced and the products will have a longer life.