Considerations when choosing chemical control options

When confronted with an above-threshold pest population, chemical intervention is often needed. However, unnecessary spraying or choosing the wrong pesticides can flare secondary pests, hasten the development of pesticide resistance, contaminate the harvested product, increase operating costs and reduce profitability.

Note: Only use products that are registered for the pest and crop, or have a valid current off-label permit.

Factors to consider when selecting insecticides include:

1. Crop and pest stage

  • How attractive is the crop stage to pests?
  • How susceptible is the crop stage to pest damage?
  • How susceptible is the pest stage(s) present to the product?
  • Is there potential for compensatory growth post-damage?
  • Will the crop stage prevent optimal control?

Physical barriers, such as pupal cases, dense crop canopies, or pest stages that are protected by plant structures may result in reduced efficacy.

If the crop is at a stage tolerant to damage, or there is time for compensatory yield to set and grow to maturity, no action or partial control by a biopesticide (or innundative beneficial release) may be sufficient. This approach conserves natural enemies already present, and reserves more effective products for later crop stages when pest attack is more likely to result in yield losses.

2. Pesticide attributes

  • How does the target pest receive the dose?
  • Is the product systemic and move (translocate) within the plant?
  • How fast does the product degrade?
  • What is the mode of action (MOA) on the target pests?
  • Is there potential for cross-resistance between similar MOAs?
  • Is there potential for multi-species activity (impact on more than one pest)?

Pesticides act either directly at the time of spraying, indirectly via dried spray residues or may require ingestion by the pest. Some newer generation ´soft´ insecticides only become ´activated´ once inside an insect´s gut.

Avoid consecutive sprays of products with a similar MOA. Insecticide Resistance Management Strategy (IRMS) may place restrictions on the number of sprays per crop or the timing of applications. Ensure that you are aware of regional recommendations.

3. Off-target impacts

  • Are natural enemy (beneficial) species present, and are they susceptible to the product?
  • Is there a likelihood of late flaring or secondary pest emergence?
  • Are there label instructions regarding bees?
  • Is there potential for crop sensitivity?
  • Are there other environmental or human toxicity risks?

Going soft early with highly selective products will conserve natural enemies and reduce the risk of flaring other pests. Many older products (particularly organophosphates and carbamates) are extremely toxic (schedule S7) poisons, and should be handled with caution. Users have a community and industry responsibility to minimise environmental, animal, surrounding crop and human contamination.

4. Other factors

  • Is the weather (temperature, humidity, wind speed etc.) suitable for application?
  • Are conditions suitable for maximum uptake
  • Is the product compatible with local water and potential product mixes?
  • Are the withholding periods compatible with harvest times or future paddock use?
  • What is the cost (product and application)?
  • Is there an economic threshold available?

Weather conditions (wind speed, temperature, humidity etc.) may impact both pesticide droplet and target pest behaviour and influence the overall efficacy of the application.

The presence or risk of residues may affect the marketability of the harvested product, and jeopardise international markets. Also be aware of regulations regarding the feeding of contaminated crop residues to stock; export slaughter intervals and related periods may not be shown on the product label; they can be obtained from the manufacturer or SAFEMEAT.

Cost can be important in determining which product is used. However, the cheapest product is not always the best as the combined impacts of insecticide resistance and flaring of secondary pests can lead to a need for additional sprays and other costs. In many cases, a single application of a more expensive but more effective and selective option will provide the best economy.

Economic thresholds compare the cost of the control method against the potential cost of crop loss if nothing is done. Economic threshold calculators available on the Beatsheet can be found here.

Further information