Black cutworm larval feeding is increasing in Van Buren County corn fields

Growers should check their corn fields for clipped or wilting seedlings, as black cutworm damage is approaching treatment threshold in some southwest Michigan fields.

With the wave of warm and wet weather we saw in early May, winter annual weed growth, which had gotten off to a slow start due to cold conditions in April, came back with a vengeance just as growers began to work fields for planting corn and soybeans. Fields that had appreciable growth of winter annual weeds as they were being worked provided attractive locations for black cutworm moths to lay their eggs. While the weeds may have been killed two to three weeks ago, in at least some Van Buren County fields black cutworm larvae survived and are clipping V2 corn plants. The following are a few things to consider when scouting for black cutworm damage.

  • Cutworms do not lay eggs on bare soil. Winter annuals or cover crops would need to have been present for the eggs to have been laid in the field. Most fall tilled fields were fairly clean in early May. You can use this information to prioritize scouting of fields.
  • Cutworm moths lay eggs sporadically. One field may have heavy infestation while the adjacent fields may have little or no damage. Scout each field to make decisions about need for treatment.
  • Black cutworm larvae are mostly nocturnal. While you can see clipping damage any time of day, in order to find the larvae themselves, you should focus scouting in the evening or early morning hours. Early instar damage from black cutworms may show up as shot holes in leaves. Plants clipped near the soil line are symptomatic of damage caused by older instar black cutworm larvae. If you find feeding along the leaf margins that leave a ragged appearance, the damage is more likely to be caused by armyworms.
  • Look around clipped plants for larvae. Bring a trowel or knife to move soil to locate larvae. The larvae can burrow into the soil or hide under soil clods. Usually larvae can be found within 1 to 1.5 feet of freshly clipped plants.
  • Different Bt hybrids have varying levels of cutworm protection. Bt corns that contain the Cry 1F (Herculex/Smartstax) and Viptera events provide a little more protection against cutworm larval feeding. Keep in mind, however, that overwhelming numbers of cutworms can cause clipping injury in just about all Bt corns, with or without soil insecticides applied.
  • You may need to apply a rescue insecticide application if there is enough clipping damage in your fields. The treatment threshold is reached when 4 to 5 percent of the plants in areas of the field are clipped.
  • There are a wide variety of insecticides labeled for black cutworm control. With the forecast calling for wet conditions over the next week, you may find it challenging to find an opportunity to spray when the material will not be washed off too soon. Michigan State University Extension bulletin E-1582 “Insect Control for Field and Forage Crops” is available online and provides excellent guidance on what insecticides are labeled for control.

MSU field crops entomologist Christina DiFonzo talks more in depth on black cutworm issues in the photo-laden resource “Q&A about the strange world of cutworms this season” that was written in the spring of 2011.

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