Western Bean Cutworm Trap Catches So Far and Crop Staging and Spray Timing

WBC egg mass with newly hatched larvae

Western bean cutworm trap counts this year have been very low so far.  Although I would normally expect at least the far southwest to be reaching peak moth flight later this week, the traps are not indicating that yet. It might happen but there are not nearly the same number of moths flying around at this time compared to previous years. So what do you do if your corn is already in tassel?  Well, scout.  Make sure there are actually eggs present in the field before making any spray decision. But those fields are very likely at low risk of egg deposition and are most likely to miss the majority of egg laying since the crop will be past the most attractive stages of pre to early tassel stage.  There are just not enough moths to place all corn fields at risk at this time.

A question I have had by a few reps lately though is…what will happen in these early corn fields during peak flight? Do we have to keep scouting? Unfortunately, yes. You want to keep scouting for at least two or three weeks after peak flight, just in case.  But the odds of eggs being deposited in fields that area already passed their ideal stages is low. They will choose corn fields in younger stages (pre to full tassel stages) or dry beans. They might lay some eggs in the early planted corn fields, but the majority of moths will be turning to the other later planted fields instead.

Also recall that the spray timing has been adjusted.  Don’t just spray in case, since this is what you have done in the past.  Some fields will not reach threshold this early in the season. Though some growers are considering having fungicide applied this week for foliar diseases during early tasseling, the optimal timing for spraying insecticide for WBC is instead, during fresh silk stage.  That guarantees that you are protecting the ear from all of the larvae that have hatched on that plant. And it aligns with proper spray timing for ear mould fungicides too.

More information on WBC thresholds and spray timing can be found here: https://fieldcropnews.com/wp-content/uploads/2018/05/WBC-Resistance-Management-Guidelines-May-2018-1.pdf

Interactive WBC trap network map showing weekly catches is here: http://www.arcgis.com/apps/webappviewer/index.html?id=a9e6a076b6cf4ff281cdff460d3ffdad&extent=-9536825.4859,4865123.8334,-7971395.1466,5987830.9048,102100