An economic threshold calculator for Helicoverpa in chickpeas

Melina Miles   October 5, 2012   Comments Off on An economic threshold calculator for Helicoverpa in chickpeas

 

Calculating the economics of control is critical to making a decision about if and when Helicoverpa populations in chickpeas require treatment. This season, for the first time, growers and agronomists have access to an on-line calculator to help them make these decisions. The calculator overcomes the need to try and remember the formulas in the field. Best of all, the calculator can be used off-line on most mobile devices, so it is available when you need to make the decision in the field. Some of the features of the calculator include:

  • Calculation of average larval density per square metre
    • Input checking data (number of larvae) and row spacing
  • Calculate an economic threshold for your specific situation
    • Input costs of control and crop value
  • Recalculate the economic threshold for a specific cost:benefit ratio

The Helicoverpa in chickpea threshold calculator is available on the Beatsheet Blog – find it under the “Economic Threshold Calculators – NEW!!” tab at the top of the page.

The calculator can be used on-line, and users with the latest browser versions of Internet Explorer (9+), Chrome, Firefox or Safari, the calculator can also be used offline. This means that after using the calculator on-line, you will still be able to access and use them offline without an internet connection. The other way to determine a current economic threshold is to use the ‘ready reckoner’ table below. When making decisions about Helicoverpa control in chickpeas, these are key considerations:

  • Larvae do not damage buds and flowers, yield loss starts to accumulate when pods are damaged as they set and fill. This means control can be delayed until pod set to minimise the chance of needing a second treatment before the crop matures. An exception to this ‘rule’ would be if control is applied to a population of small-medium larvae during late flowering to remove them so they are more easily controlled and not in the crop when it reaches pod set.
  • Use a beatsheet to sample chickpeas. Using a stick that is a metre long to ‘beat’ the crop simplifies the estimate of larval density. Watch the short Youtube video on how to use a beatsheet in chickpeas.

  • Try to make an assessment of the H. amigera  and H. punctigera numbers in the crop. This is particularly important if you are attempting to control medium to large larvae as H. armigera may be less susceptible to some older products (e.g. synthetic pyrethroids).  You may recall a recent article on the Beatsheet by Dr Lisa Bird on the results of resistance testing over summer – the level of resistance to synthetic pyrethroids had increased over previous seasons.On the Downs this season, the population of Helicoverpa in crops is made up of both H. armigera and H. punctigera. Take this into account when making a decision about which product to use.

For a more detailed discussion of Helicoverpa management in chickpeas, the formulas for calculating an economic threshold, and background information on how the thresholds were devised you can read previous posts on the Beatsheet Blog. http://thebeatsheet.com.au/category/chickpeas/