Western Bean Cutworm Fact or Fiction – Fact #2 Trap Counts

Fact or Fiction #2 – “Some trap sites in 2010 were catching 1000s of moths per day!”

This is completely false.  At least from the data that came in to me from the 471 trap sites being monitored last year.  No trap location caught more than 600 moths in ONE WEEK, let alone on a per day basis.  And it is the dry bean field traps that caught a lot more moths then the corn field traps.  The average dry bean trap caught 225 moths per week during peak flight in 2010, while corn traps were only catching 36 per week.  The highest trap count site caught 569 moths in one week and was a dry bean field in the Zurich area.  If someone is telling you they were catching 1000s of moths per day, they are greatly exaggerating.

Unfortunately trap counts don’t equate to damage levels experienced in the field.  This somewhat makes sense.  We only catch males in these traps.  The lure contains the sex pheromone of the female.  Females are still happily flying around, picking and choosing which fields to lay their eggs in.  And they are choosy.  They are going to select the fields that are in the most ideal corn stage (pre-tassel to tasseling) to lay their eggs in.  So even if a trap next to a field is catching a  lot of males, it is not indicating what the females are doing.

Traps do tell us when moths start to fly around.  And they tell us when peak moth flight takes place.  Knowing when peak moth flight occurs tells us when the most mating is going on and when to expect the most eggs to be laid.  If your corn field is already past flowering when peak flight occurs, you know your field is safe.  And you also know to look at other fields down the road that may be less advanced and still attractive to the moths.

Don’t get wrapped up in the numbers game.  Use the traps wisely.  They are there to tell you when to scout.  Don’t be fooled into thinking they tell you that you need to spray without scouting first.