Understand the risk of snails being present and potential yield losses associated with snail feeding damage.
- Snail numbers can increase in seasons with wet springs, summers and autumns. Snails need moisture to be active and rainfall is the main trigger for activity. They are generally actively feeding and breeding when conditions are moist.
- Snails and slugs live in areas where abundant ground cover and vegetation provides ideal moisture levels and shelter.
- Damage to canola seedlings often results in the death of the plant, which means major production losses.
Assess the costs and benefits of taking preventative action such as removing any ‘green bridge’ or destroying stubble.
- Control of summer weeds (‘green-bridge’) results in fewer harbourages for snails over summer and also increases the effectiveness of baits by removing food competition.
- Weed control along fence lines, around dams and in remnant bush decreases breeding refuges for snails.
- Even burning of stubble can reduce snail numbers by 80–100%; a patchy burn can lead to 50–80% kill, however, soil type and risk of wind erosion needs to be taken into consideration.
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 cleaning costs at harvest to remove snails.
- Consider withholding periods — Baiting must finish two months prior to harvest to prevent bait becoming a contaminant of harvested grain. There is zero tolerance of bait contamination of grain.
- Compare the costs ensuring you allow for the possibility of further treatment. Snail mortality after baiting is between 60–90% for mature round snails and 50–70% for mature pointed snails. More bait points per hectare rather than higher concentrations of active ingredient have been shown to result in better kill rates. Bait degrades in UV light; degradation rates are reduced as day length shortens.
- Selection of pellets may be influenced by the opportunities to control other pests.
- Best practice is to bait without applying any other treatments, therefore the cost of going over the needs to be included as well as the cost of the pellets and any additional time needed to prepare and spread.
- 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 and climatic conditions. The economic calculator can assist with this decision.
Consider risk and associated costs or savings of no treatment or delaying treatment.
- The key is to start baiting before snails lay eggs in autumn.
- It is essential to spread pellets when snails are active after rain and to apply at the highest label rate if numbers exceed thresholds or if crop damage is occurring.
- Spring baiting is ineffective.
- If considering delaying treatment and numbers increase factor in the increased bait rates, withholding periods and costs of cleaning grain at harvest.
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 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 about it.
Undertake a ‘what if’ scenario analysis to see what impact changing variables (e.g. grain price and seasonal conditions) have on the economic outcome.
- 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 integrated pest management system.
- Controlling snails before egg laying commences is fundamental to successful integrated control. This will occur about 2–3 weeks after the first heavy rains in autumn.
- Consider costs and benefits of removal of stubble and green bridges, other pests and diseases, biological impacts and risks of resistance to chemicals.
To assist in assessing the economic risk and financial costs associated with various treatment strategies go to MyEconomicTool