Understand the potential yield losses associated with aphid feeding damage and possible transmission of the barley yellow dwarf virus (BYDV).
- Potential yield loss is variable. Yield loss from BYDV is dependent on aphid vectors to be present from crop emergence. They are present if a green bridge occurs over summer. Feeding damage to crops is dependent on the size and growth rate of the aphid population, the growth stage of the plant at infestation, the effectiveness of natural enemies such as wasp parasitoids, ladybird beetles, hoverflies and aphid fungal infection and the potential yield of the crop.
Assess the costs and benefits of taking preventative action.
- The cost of preventing aphids for BYDV transmission early in the season and feeding damage from aphid infestations from tillering should be weighed against the savings of non-action in the event there was no green bridge over summer or no aphid infestations occurred during the year. Costs include the opportunity cost of the cost of seed treatment or spray, biological costs such as also killing natural enemies of aphids and potential risk of resistance build up.
Assess the cost and benefits of controlling ‘green bridge’ (self-sown cereals and grass weeds).
- These plants will host aphids and virus. Destroying them in advance of sowing will also conserve soil moisture and lessen the probability of disease carry-over such as rust.
Compare the costs, benefits, and risks of each management option against doing nothing.
- What are the likely outcomes of each management option? When the result of treatment is unknown consider the most likely (expected), as well as the worst and best results from each treatment option.
- When calculating the cost of non-treatment, assess the potential risk of yield losses and grain quality downgrades. This will depend on size of the aphid population and how early the infestation starts or is detected in the crop. Infestation late in the season doesn’t usually have a significant yield impact. Quality reductions such as lower hectolitre weights can also reduce revenue.
- When comparing control options, consider both current and the possibility of further treatment costs.
- Selection of insecticide may be influenced by the opportunities to control other pest insects.
- If applying insecticide at the same time as other treatments only assess the additional cost of application, i.e. the cost of going over the paddock is not included as it would have been incurred anyway. The additional cost is the cost of the insecticide and any additional time needed to prepare and apply.
- Consider costs and benefits for both ground and aerial application methods.
- Consider choosing a treatment option where the expected return is sufficient to offset its risk of the treatment. We all have different attitudes to risk when making decisions. The probability (risk) of outcomes can be affected in terms of responsiveness (efficacy), application rates, products, application methods, treatment costs, climatic conditions and crop prices. The economic calculator can assist with this decision.
Consider risk and associated costs or savings of no treatment or delaying treatment until threshold level of aphids is reached.
- To avoid unnecessary spraying, regularly monitor aphid numbers at several sites to gain true representation of population size and their distribution through the crop and whether numbers are growing. Numbers may reduce due to heavy rainfall or by natural predators such as wasps, ladybeetles, lacewings and hoverflies.
- Alternatively, if no action is taken and the aphid population multiplies the treatment cost and yield losses could be higher.
- Spraying after crop flowering is normally less economic as yield losses are usually limited to shrivelled grain size (quality).
Consider the potential risk of re-infection and costs of further treatment.
- The length of time an insecticide is effective depends on the active ingredient and rate of application. Climatic conditions and the remaining length of the growing season will affect the likelihood of follow up treatments.
Ignore all previous treatment costs in assessing current management options.
- Costs associated with previous treatments should be ignored as they cannot be recovered. They are ‘sunk costs’, i.e. even if the current treatment results in the crop are not breaking even, provided the additional benefit of the treatment is greater than the cost of treatment, then the net return from treatment is still better than doing nothing.
Undertake a ‘what if’ scenario analysis to see what impact changing variables (e.g. grain price and seasonal conditions) have on the profits.
- Some variables can influence decision outcomes but are not directly controllable, including fluctuations in wheat price, the value of the Australian dollar and seasonal influences. But they need to be considered, even if we cannot include them directly. A ‘what if’ analysis may help you in your decision making.
Consider using an integrated pest management system and include a resistance management strategy into your spray program.
- Include a resistance management strategy into your spray program to reduce the chance of aphids and other non-target pests becoming resistant. If monitoring indicates the need to spray, then insecticide choice (such as ‘soft’ on natural enemy chemicals) and rotation of chemical groups needs to be considered, as part of an integrated pest management strategy.
To assist in assessing the economic risk and financial costs associated with various treatment strategies go to MyEconomicTool