Pre-crop
Understand the potential risk of a locust and grasshopper plague and potential yield losses associated with feeding damage.
- Locusts and grasshoppers are a chewing pest that can cause considerable damage, including complete defoliation if pest populations are high enough.
- Crops that are beginning to dry off when locusts begin to fly are susceptible to damage; locusts cause little if any damage to crops that have dried off.
- 'Green bridge' feed is required for the autumn generation of pests to lay sufficient eggs to pose a risk for crops in spring.
- High risk: locusts were on your farm for one to four weeks during April and May and you observed egg laying.
- Moderate risk: locusts were on your farm for less than a week and there was egg laying in isolated areas.
- Low risk: locusts pass through your property and you observe no egg laying.
Assess the costs and benefits of taking preventative action.
- If there was locust activity in autumn, check for egg-bed hatching in spring and monitor hopper numbers.
- Insecticides are not effective repellents against attack. It is not possible to spray prior to a swarm or band arriving to prevent the locusts entering a crop.
Assess the cost and benefits of controlling against the development of a ‘green bridge’ (self-sown cereals and grass weeds) in order to reduce exposure to attack.
- These plants will support egg laying of locusts or hoppers. Destroying them, prior to sowing will also conserve soil moisture and lessen the probability of disease carry-over such as rust.
In-crop
Compare the costs, benefits and risks of each management option against the alternative option of 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. Results from treatment will depend on: age of locust, crop stage, amount of green matter, wind conditions and time of day of spraying.
- Are there any options to minimise damage? Cutting crops for hay or windrowing them in preparation for harvest can minimise locust damage or eliminate the need for chemical control. Baling or silaging crops and pastures before locusts hatch is another management tool.
- If applying insecticide at the same time as other treatments only assess the additional cost of chemical 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 specific 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 the time it will take to spray for control – will contractors be required? If so, include them in the costs.
- Check for and assess the cost of off-target impacts of spraying, including nearby livestock, bees, aquaculture, organic production, dams and waterways. Ensure that all required buffer zones are observed to minimise environmental impacts.
- Observe insecticide withholding periods and consider implications associated with having to possibly harvest later than planned.
- Consider choosing a treatment option where the expected return is sufficient to offset 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 risks, costs or savings associated with a no treatment option or delaying 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 hopper or locust population and how early the infestation starts or is detected in the crop. Crops most at risk are those containing green plant matter. Locusts cause little if any damage to crops that have dried off.
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 are ‘sunk costs’ and should be ignored as they will have no impact on the economic benefit of taking action now, i.e. even if the current treatment results in the crop not breaking even, provided the additional benefit of the treatment exceeds the cost of treatment, then the economic return from treatment will still be higher than doing nothing.
- Review receival standards for locust or hopper contamination and assess risks and costs of possible downgrades. Receival standards vary with crop type. At time of writing for cereal crops (wheat, durum wheat, barley, triticale and oats) the maximum allowed live or dead is three field insects per half litre of grain or seed. One locust counts as one field insect.
Post-crop
- There are no post crop economic considerations.
To assist in assessing the economic risk and financial costs associated with various treatment strategies go to MyEconomicTool