Sebe Brown, Dr. David Kerns, LSU AgCenter Entomologists, Dr. John S. Kruse, Cotton and Feed Grain Specialist
This week, Dr. David Kerns and I scouted corn fields at V1 in Evangeline Parish for cutworm damage. Cutworms are usually problems in reduced tillage or no till fields that received a late burndown application leaving weed hosts. However, the fields we scouted were very clean and above ground damage was evident with clipped leaves and larvae being easily found on the tops of rows. Starting clean can help alleviate many problems from early season insect pests; however, clean fields should be routinely scouted for cutworms.
The largest amount of the damage was found in non-Bt refuge corn. Fortunately, the larvae were feeding above the soil surface clipping early leaves and not burrowing down to the root zone damaging the growing point. Seedling corn (up to V4) can withstand injury from cutworms as long as the growing point has not been damaged.
Thresholds for cutworms in Louisiana corn are 6 to 8% damage from above ground cutting or 2 to 4% from below ground boring. With cooler weather moving into Louisiana, cutworms may be located closer to the soil surface in seedling corn. Warmer weather drives the cutworms to burrow down deeper into the soil increasing the risks of having corn injured at the growing point.
Insecticide seed treatments should not be expected to give adequate control of cutworms and Bt technology can provide some protection. VT3 Pro, VT2 Pro, Herculex and SmartStax technologies should help reduce cutworm injury: however, large larvae may overcome these traits. Large larvae are less susceptible to Bt toxins than small larvae.
If an insecticide application is deemed necessary, a relatively low label rate of a pyrethroid will reduce cutworm injury. Bifenthrin would be a good choice due to its soil activity.