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.