Pre Crop

  • Is your paddock susceptible to desiantha weevil adult or larval damage?
  • Understand the potential yield losses associated with desiantha larvae feeding damage to cereals and adult feeding damage to canola and lupin crops
  • Assess the costs and benefits of taking preventative action

In crop

  • Compare the costs, benefits, and risks of re-sowing
  • Ignore all previous treatment and sowing costs in assessing current management options

Post Crop

  • Consider using integrated pest management system and include a resistance management strategy into your spray program to reduce the chance of desiantha and other non-target insects developing resistance to insecticides.

Further details:

Pre Crop

 

  • Is your paddock susceptible to desiantha weevil adult or larval damage?
    • Were desiantha weevil present in the paddock last year?
    • This native weevil is more likely to build up to damaging numbers after grassy pastures and when summer rains create a green bridge that enables the adult weevils to reproduce.
  •  Understand the potential yield losses associated with desiantha feeding damage
    • Larvae feed underground on germinating cereal seeds or stems often killing plants or causing abnormal or stunted growth.
    • Adults feed on canola and in sufficient densities can cause seedling death
  • Assess the cost and benefits of taking preventative action
    • Larvae of desiantha weevils cannot be successfully controlled post cereal emergence with insecticides as they stay underground. Therefore, if paddocks are known to have high populations of desiantha weevils,  the only options are destroying the green bridge prior to sowing,   seeding at a higher rate, applying an insecticide with the seed,
    • Adult weevils can be controlled post canola crop emergence if sufficient damage is occurring.
    • If the population size is not known the cost of preventing weevil damage to crops should be weighed against the savings of non-action in the event of no serious damage occurring. Costs include the opportunity cost the cost of seed treatment or costs of destroying the green bridge (if done exclusively for desiantha control). For example, if weevils don’t exist in large numbers or seed treatment is not effective on larvae how much better off would you have been if you had not taken unnecessary steps to prevent them.

In crop

  • Compare the costs, benefits, and risks of re-sowing
    • The only in-crop treatment for control of desiantha weevil larvae is to reseed cereals with insecticide coated seed. 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.
    • Weigh up the costs and risks against the potential income for re-sowing the crop.
    • Consider other benefits such as protection from wind erosion.
  • Ignore all previous treatment and sowing costs in your assessment in assessing current management options
    • Costs associated with previous treatments and sowing should be ignored as they can’t 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 net return from treatment is still better than doing nothing about it.

 

Post Crop

  • Include a resistance management strategy into your spray program to reduce the chance of desiantha weevils and other non-target pests becoming resistant. If monitoring indicates the need to spray, then insecticide choice and rotation of chemical groups needs to be considered, along with appropriate spray application. Ensure summer weed control occurs in all paddocks to be sown to cereals or canola.