Earth mites - economic considerations for management

There are many economic and financial implications that need to be considered when choosing a management option. These may include:

Pre-crop

Understand the potential yield losses associated with earth mite feeding damage.

  • Economic damage can occur as soon as canola seedlings break the soil surface if earth mite numbers are high.
  • More earth mites are typically found in canola that has been sown after pastures than canola sown after cereals.
  • Damage to crops only occurs when earth mites hatch after seven consecutive days of temperatures below 20°C combined with rainfall in autumn. If there is a warm start to the season, crop damage is unlikely.

Assess the costs and benefits of taking various preventative actions in the spring period in the year prior.

  • Assess the costs and potential benefits of taking preventative measures such as spraying in spring, controlling weeds in the previous year’s crop and/or grazing pastures.

Assess the cost and benefits of taking preventative action immediately prior to or at seeding.

  • Assess the costs and potential benefits of undertaking a bare-earth spray immediately after seeding and/or using insecticide-treated seed.

In-crop

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. Some earth mites are resistant to chemical applications containing synthetic pyrethroids.
  • When calculating the cost of not treating the mite infestation, assess the potential risk of seedling loss. This will depend on size of the mite population and how early the infestation starts or is detected in the crop. Infestations late in the season do not have a yield impact.
  • Compare the costs ensuring you allow for the possibility of further treatment.
  • Selection of insecticide may be influenced by the opportunities to control other insects.
  • If applying insecticide at the same time you would with other treatments, only assess the additional cost of applying the chemical, i.e. the cost of going over the paddock is not included as it would have been incurred anyway. The relevant (marginal) cost is the cost of the insecticide and any additional time needed to prepare and apply it.
  • Consider choosing a treatment option where the expected return is sufficient to offset the 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.

  • To avoid unnecessary spraying, consider control measures in high risk paddocks e.g. canola sown after pasture or weed control after a prior cereal crop.  
  • Alternatively, if no action is taken and the mite population multiplies the treatment cost and yield losses could be higher.

Ignore all previous treatment costs when assessing current management options.

  • Costs associated with previous treatments should be ignored as they cannot be recovered. They are 'sunk costs' and have no bearing on the economic return from taking action at this stage of the crop, i.e. even if the current treatment results in the crop not breaking even, provided the additional benefit of undertaking the treatment now is greater than the cost of treatment, then the economic return is still going to be better than doing nothing about it.

Undertake a ‘what if’ scenario analysis to see what impact changing variables (e.g. grain price and season conditions) have on the likely 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.

Post-crop

Include a resistance management strategy into your spray program to reduce the chance of earth mites and other non-target pests developing resistance.

  • An integrated approach to pest management where paddock selection and weed-free fallow periods are used in combination with justified insecticide usages will be more sustainable.

To assist in assessing the economic risk and financial costs associated with various treatment strategies go to MyEconomicTool

Where to go for expert help

Tamara Stretch
+61 (0)8 9881 0225
Page last updated: Tuesday, 2 September 2014 - 12:04pm