Black Cutworm and True Armyworm May Cause Problems This Year

States to the south of us have been reporting intense black cutworm moth captures over the last few weeks.  The continuous storm fronts that keep moving across Ontario could be carrying some of these moths to us.  In addition, rain has kept us from getting into the fields to manage the annual weeds (especially chickweed) which the female moths are attracted to laying their eggs on.  The later we get into our fields and plant corn, the bigger the larvae may be once they start feeding on the tiny corn seedlings.  Also, don’t assume that all Bt corn protects from black cutworm.  Agrisure Viptera hybrids will provide good control, while hybrids containing Cry1F (Herculex I, Herculex Xtra, Genuity SmartStax, Optimum Intrasect, and SmartStax) may only give good control of younger larvae.  Rescue treatments can also be effective if infestations are spotted and controlled in time.  Expect to be scouting seedling corn fields to determine if control is needed.  More information on black cutworm scouting and management is available at:

True armyworm could also be a risk this year.  We tend to see outbreaks following a cool, wet spring as this miserable weather impacts the parasites that help to control true armyworm.  Expect to start scouting wheat around mid May.  Examine plants from five locations in your field to determine the level of infestation. Winter cereals can be as attractive to moths as grassy weed borders so the field may be infested throughout. During the day, look for true armyworms under the crop residue and soil clods. Their frass will also be visible on the ground and lower foliage.  It is best to scout during the evening or very early morning (before sunrise) with a flashlight to observe the larvae feeding.   If there are reports of outbreaks, then corn fields will also need to be scouted.   Details on scouting, management strategies and control are available at:

3 thoughts on “Black Cutworm and True Armyworm May Cause Problems This Year

  1. I have some armyworm crawling in tomatoes. Will they do economic damage. During midday I didn,t see feeding. 3/4 in long.

    1. Hi Henry

      My guess is no they won’t. Tomatoes are not listed as a key host crop. I suspect they are just marching through the field to get to the next grass crop like wheat or corn. But Janice LeBoeuf is going to contact you to come take a look.

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