– Economic Considerations

Pre Crop

  • Assess whether cockchafers/larvae exist in the soil in damaging numbers
  • Understand the potential yield losses associated with cockchafer feeding damage
  • Assess the costs and benefits of taking preventative action

 

In crop

  • Compare the costs, benefits, and risk of each management option against doing nothing
  • Ignore all previous treatment and sowing costs in assessing current management options

Post Crop

  • Consider the costs of continuing monitoring and treatment  

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Further details:

Pre Crop

 

  • Assess whether cockchafers/larvae exist in the soil in damaging numbers
    • After seeding, control for cockchafers is difficult. Assess numbers prior to seeding into high risk paddocks, especially paddocks that had cockchafers present in the year before.
    • Larvae feed on underground plant parts, causing them to wither and die potentially leading to large bare areas. Cereal crops after pasture are more likely to be damaged with damage worse near tree belts

 

  • Understand the potential yield losses associated with cockchafer feeding damage
    • Infestations of 20 grubs per square metre can cause crop thinning while more than 50 grubs can completely destroyed crops.

 

  • Assess the cost and benefits of taking preventative action
    • Cockchafers cannot be successfully controlled post crop emergence with insecticides as they stay underground. Therefore, if paddocks are known to have high populations of cockchafers the only options are mixing registered insecticide treatments with seed and/or using a higher seeding rate.

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.
    • Chemical control is only effective if the chemical can reach the grub in the soil. As they do not come to the surface, spraying the soil surface is of no benefit.
    • It has been found that re-sowing affected areas will provide protection from wind erosion and return a modest yield. The initial feeding activity has decreased significantly by the time the resown crop germinates. Weigh up the costs and risks of re-sowing against its potential benefits and income (value of the yield of the new crop).

 

  • Ignore all previous treatment and sowing costs in your assessment in assessing current management options
    • Costs associated with previous treatments should be ignored as they are “sunk costs” and will have no effect on the economic outcome of taking some course of action at this stage of the crop cycle.  i.e. even if the current treatment results in the crop not breaking even, provided the additional benefit of the treatment exceeds the costs then the net return from treatment is still better than doing nothing about it.

 

Post Crop

 

  • Consider the costs of continuing monitoring and treatment
    • Some species have a one year life cycle, others have a two year life cycle. Look for adults from November onwards. Adults can be sprayed. Continue to look for cockchafer larvae when the ground is being prepared for planting the following year.