Western Bean Cutworm Thresholds for High Risk Fields in Ontario

My crew is finding many corn fields at threshold levels of western bean cutworm (WBC) in the “high risk areas” of Bothwell and Tillsonburg. We have learned over the last few years that Bothwell and areas around Tillsonburg in particular (higher sandy soil areas) are prone to high levels of WBC infestations. Other areas of Southern Ontario might also reach threshold too so at least a one time scout anytime from pre-tassel to late tassel stage is recommended in fields that are not planted to Agrisure Viptera, SmartStax or Herculex hybrids.  Essentially any non-Bt or YieldGard Bt (Cry 1Ab) corn fields are at risk.

Scouting Technique and Threshold in Corn: Scout 10 plants in a row in 10 areas of the field.  In non-Bt corn or transgenic corn that does not provide any protection against WBC (ie. YieldGard Bt containing Cry1Ab only), if 5% of those plants have egg masses on them, a spray is warranted.  Time the spray application for just after egg hatch when small larvae are present at the top of the plant.  Egg hatch occurs a day or two after the egg masses turn purple (typically 5-7 days after being freshly laid).  But in this heat, that can be shortened to 3 or 4 days.

Is there a threshold for Cry1F corn yet?  No, not yet.  In heavy infestation years, hybrids with Cry1F (Herculex and SmartStax) may see some damage but they at least give approx 70% control.  If we do set a threshold, it would be higher than the current 5% threshold for unprotected corn.

Two helpful scouting videos include:



Control Options: In these extreme temperatures, insecticides should be applied in the evening when temps are below 24 degrees C.

Click on the table below to enlarge.2013 Corn Products for WBC

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