Armyworm Again! Scouting is Advised

I was concerned about the potential risk for armyworm this year, given that we had a cool, wet April which is not ideal for their natural enemies.  But to have back to back armyworm years is rare.  Will Ontario beat those odds this year?

I have had reports of armyworm being present in many wheat fields in Chatham-Kent though not at threshold yet.  Another report came in just yesterday of a field in Harrow that was near threshold, though the armyworm were still small and had not done much leaf feeding yet.  It doesn’t take long for these smaller larvae to grow and  start clipping heads though so don’t underestimate these small larvae.  They are actually the best size to get good control of.  If armyworm reach threshold (5 per square foot) in wheat, control is advised, as long as most of the larvae are still small.  Once they get to be bigger than an inch, they are more difficult to control.  Also pay particular attention to the pre-harvest intervals as the PHIs for the products registered in cereals range from 14 to 28 days to harvest.

This does not mean however, that everyone should tankmix some insecticide in with their fusarium control this week “just in case”.   Tankmixing “just in case” is NOT sound integrated pest management.  Applying insecticides when they are not necessary can lead to mother nature biting back.  These profolatic sprays kill off non-targets including natural enemies of our plant pests which take a lot longer to build up again in numbers to help control the pest.  It starts a cycle where, in the absence of any natural enemies, the pest becomes a problem, year after year.  You will also fail at effectively controlling either armyworm or fusarium this way.  Fusarium and armyworm require very different spray strategies.  The nozzles, nozzle configuration, water volumes, and pressures are different for fusarium versus armyworm control.  For armyworm control, you want to use water volumes of at least 20 gallons of water per acre, with nozzles that give a medium to fine droplet size, with best control found when nozzles are set at 30 degrees forward and 30 degrees back to get good coverage down into the canopy of the crop.  Fusarium nozzles are set at a very different angle to target the wheat head only which is very important for fusarium control but won’t get to the armyworm feeding below.  And you must spray for armyworm at night when the insect is actively feeding on the plants.

Wheat is not the only crop at risk from armyworm.  Forages and corn also need to be scouted these next few weeks.  I have not had any reports of armyworm in forages or corn yet.  But that does not mean they are not there.  Everyone needs to take a look at these crops at risk.

Scouting Thresholds and Control Options for Wheat:

Scouting Thresholds and Control Options for Forages:

Scouting Thresholds and Control Options for Corn:


3 thoughts on “Armyworm Again! Scouting is Advised

  1. West Nipissing, Ontario between Sudbury and North Bay in Northern Ontario is being hit by army worm now. The farmers that were hit first appear to all have purchased their seed from Southern Ontario. Can army worm be spread by contaminated seed from the previous year? We purchase our seed locally. We need to know so we won’t repeat the cycle next year.

    1. I’d like to confirm that it is armyworm. Is this in corn or forages? Pics would be great if you could send to They would not have come from the seed. True armyworm flies into Ontario in the spring and lays eggs. First generation is what we deal with in May/June. Those larvae then develop into moths and could have made their way up to you via storm fronts. Those moths would have laid eggs and now there would be a second generation of larvae feeding. But a pic would help me ID for sure.

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