Mites (bryobia mite and balaustium mite) 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 mite feeding damage.

  • Economic damage generally only occurs if these mites are present in very high numbers, especially if seeding into green bridge or if crop is moisture stressed. Under good growing conditions crops outgrow damage.
  • Mite numbers are greater in crops sown after pastures than after weed-free crops.
  • Damage is most common in very early-sown crops after summer rain, when mites hatch and multiply on summer weeds prior to sowing crops.

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 previous year’s crop and/or grazing pastures.

Assess the cost and benefits of controlling summer weeds to reduce potential feed source.  
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 all preventative actions such as controlling any green bridge with chemical, a bare-earth spray immediately after seeding and/or 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 mites are more tolerant to chemicals than others, e.g. organophosphates do not control balaustium mite but have efficacy on bryobia mite.
  • When calculating the cost of non-treatment, 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. Infestation late in the season does 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 marginal cost of application, i.e. the cost of going over the paddock is not included as it would have been incurred anyway. The marginal cost is the cost of the insecticide and any additional time needed to prepare and apply.
  • 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.

  • To avoid unnecessary spraying, monitor mite damage and numbers. 
  • 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 in assessing current management options.

  • Costs associated with previous treatments should be ignored as they are ‘sunk costs’ and will have no direct effect on the economic outcome of a decision taken now, 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, then the economic gain from treatment will still be 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 projected economic outcomes.

  • 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 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 - 12:27pm