Western Bean Cutworm Action Thresholds

Many questions are starting to come in regarding WBC.  Just to help clarify what the action thresholds for western bean cutworm are, here is a quick summary:

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 (click here to see corn trait list and insects they control), if 5% of those plants have eggmasses 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 eggmasses turn purple (typically 5-7 days after being freshly laid).  For a list of products registered in corn, click here.  In these extreme temperatures, insecticides should be applied in the evening when temps are below 24 degrees C.  I’d recommend waiting to spray until after Thursday of this week when nighttime temps start to go back down to low 20s, high teens.

Is there a threshold for Cry1F corn yet?  No.  As you have read in past blogs and articles, Cry1F (eg. Herculex, SmartStax) only provides approx 70 to 80% control for WBC.  So you can experience some damage in heavy infestations. Eventually we may set a much higher threshold for Cry1F corn but for now, we don’t know what that is.  The research is taking place right now.  Populations would have to be very high to justify spraying Cry1F corn.  70 to 80% control is still better than not planting a Bt hybrid that protects against WBC.  The Agrisure Viptera Bt corn does provide excellent control (nearly 100%) of WBC will not need a potential higher egg threshold.

In Dry Beans: There currently are no thresholds established for dry beans yet.  However, research suggests that insecticide applications are most effective when targeted as soon as pod feeding can be easily found in the field (ie..if after a half hour of scouting you only find a few pods with feeding it is not worth spraying).  Pod feeding typically takes place 10 to 21 days after peak moth flight so having a trap at the field location helps determine when moth peak occurs.  Ontario has not yet reached peak moth flight this year.  To see a  list of products registered in dry beans, click here.  If a corn field directly adjacent to the dry bean field has reached threshold, then the dry bean field should be considered at risk.  Plan to scout that field for pod feeding and spray if warranted.