Above photo: Purdue University. Published in May 6, 2022 issue of Purdue Pest & Crop newsletter
Time will tell whether this turns out to be a cutworm year in corn fields or not. Purdue experts urge farmers to be prepared to scout for black cutworm as the crop gets planted and emerges.
John Obermeyer and Christian Krupke, Purdue entomologists, recently authored an article for Purdue Pest & Crop newsletter on the pest.
“The timing of intensive moth captures, (i.e. 9 or more moths caught over a 2-night period), over the past several weeks and subsequent larval development may challenge corn that has yet to be planted,” they said on May 6. “This will be especially true with for fields with abundant weeds (esp. chickweed) because of delayed weed control.”
A recent pheromone trap report for black cutworm moths revealed that intensive captures of the moths at Northeast Purdue Agricultural Center in Whitley County has recently occurred. This does not guarantee future damage from larvae, but it sets the stage for that possibility. Scouting will be needed to confirm damage, and whether that damage meets or exceeds economic thresholds.
“Based on the growth development model, it takes approximately 300 heat units (50ºF base) from egg hatch to early 4th instar; this is the life stage when black cutworm larvae begin to cut plants,” they said. “Some leaf injury may be present before then, and this is an ideal time to treat – foliar insecticides will be much more efficacious when caterpillars are smaller and before they have begun cutting plants.”
The cooler temperatures we have experienced in past weeks delayed black cutworm larval development. “This means that the small percentage of corn planted the past weeks will likely outgrow larval development and not be vulnerable,” they said. “But for those fields yet to be treated with herbicides and planted, emergence timing may coincide with hungry young caterpillars deprived of their weed hosts – thus threatening emerging corn.”
The experts concluded by saying that we’ve had relatively low pressure from this pest in recent years, and that may have lulled producers into a false sense of security with the seed-applied insecticides and/or Bt-traited corn. “…these offer plant protection that is inconsistent, at best.” they said. “This is a case when timely scouting and rescue treatments of foliar insecticides when necessary are the tried and true approach with this stand reducer.”
Find Obermeyer and Krupke’s original article at https://extension.entm.purdue.edu/newsletters/pestandcrop/.