Monitoring for insect pests and beneficials
Timely crop checking is essential to detect pest populations before they can cause significant crop loss. For some pests, it is critical to detect them before they are too large to control effectively, or become entrenched in feeding sites where they cannot be controlled.
The frequency of crop monitoring is determined by:
- Susceptibility of the crop at each stage of development
- The risk posed by the pest in terms of speed of population build up and crop loss
- How close pests are to threshold, and a decision needs to be made on control. For example, as the pest population approaches threshold, the frequency of sampling might increase e.g. two checks a week instead of one.
Economic thresholds are determined for a specific sampling technique. For example;
- Thresholds for helicoverpa in field peas requires the population estimate to be based on sweep net sampling.
- In summer pulses, thresholds of helicoverpa are based on estimates derived from beatsheet sampling.
- Be aware of which sampling technique is appropriate for each pest and crop stage.
- Row spacing makes a difference to the population estimate
- conversion factors are used to adjust for different row spaces to standardise pest density estimates.
Getting a sound estimate of the pest population in a paddock is not always easy.
Factors that influence accuracy of estimates;
- Differences in crop establishment
- Patchy pest distribution
- Proximity to sources of pests
- Where there is a lot of variation in the paddock, or pest distribution is typically patchy – take more samples rather than fewer.
- If pest density is around threshold – take a few more samples – to give you extra confidence in making a decision about control.
The edges of fields are often quite different to the rest of the field. For many pests the borders are not sampled but for those pests, that enter fields along the edges – monitor along borders e.g. pea weevil, mites and aphids. Try to rotate sampling areas within the field on different occasions. Check across the normal direction of spraying.
Monitor for beneficials at the same time as pests. In general, the same sampling techiques will work for both pest and beneficials.
Traps (e.g. pheromone and light traps) are useful for getting an early warning of pest migration into the local area, or emergence of pests from a local source. Trapping is rarely a substitute for direct sampling of crops to assess pest densities. Always record insect numbers found during monitoring.
Keeping records of pest and beneficial density in crops is essential for making decisions about management. A pre-formatted sheet makes recording in the field easier, and ensures you don’t forget to record specific information e.g. crop growth stage, % flowering, size of larvae. Standardised recording sheets ensures that the same data is collected, regardless of who checks the paddock. It also makes it easy to transfer the field data to a spreadsheet to review changes in pest density over time.
Example of an insect monitoring sheet – pulses (140 kB PDF)