The northerly migration of black cutworm moths into Iowa from Texas and Mexico is an annual event. This insect is an occasional pest of corn, yet it deserves our attention because of its damage potential. The Integrated Pest Management Program at ISU coordinates a moth-trapping program with cooperators in about half of Iowas counties. These traps contain a pheromone (a chemical attractant) that catches male moths.

How is the trap information interpreted? The capture of eight or more moths on two consecutive nights is enough to suggest the potential for cutworm injury. Growing degree days are then predicted over the next several weeks to estimate when first cutting is expected to occur.

Do the trap catches indicate a cutworm outbreak? Definitely not. It is very important to remember that trap catches only indicate that moths have arrived in an area. Traps do not predict the amount of cutting that will occur, in what fields cutting will happen, or where the moths laid their eggs. Dont be misled by advertising that claims that a cutworm outbreak will occur in your county just because moths were trapped. Scout seedling corn near the first cutting date to determine if a problem exists. Then, apply insecticides if they are needed.

Should a farmer use a preplant insecticide just for cutworms in first-year corn? No. Insecticide applications for cutworms in first-year corn are nothing more than insurance, and they very seldom provide an economic return. The integrated pest management approach has always been to scout the field, and apply a rescue treatment if needed.

When should I begin scouting? Begin scouting a couple of days before May 12 in southern Iowa. Begin scouting in other regions of the state a couple of days earlier than the dates on each section of the map on the opposite page. Predicted cutting dates were provided by Elwynn Taylor, extension climatologist.

What is the value of the predicted cutting dates? They help you anticipate cutting so that fields can be scouted before the predicted damage. Remember that trap catches cannot be used to predict the severity of a cutworm problem or the need for an insecticide treatment.

How should I scout a field? Begin walking the field a couple of days before cutting is predicted. Look for cutworm injury on the corn leaves (see photo, opposite page). This injury will help you pinpoint fields with potential problems. As the April 22 ICM newsletter mentioned, dingy cutworms also feed on leaves, but rarely cut plants. Therefore, we suggested that you find and identify cutworms to determine if cutting is expected to occur. When you find leaf feeding, mark 100 plants in a row with stakes or flags, and scout these same plants for cutting over time. Do this several places in the field. This way you can monitor the progress of damage and observe what is happening in the field.

What economic threshold should I use? When cutworms average less than 34 inch in length, consider an insecticide if 2 to 3 percent of the plants are wilted or cut. If cutworms are longer than 1 inch, treat if 5 percent of the plants are cut. Scout fields until plants have five fully-developed leaves. Once plants reach this size, it becomes very difficult for cutworms to cut the plant.

Should I scout my fields if a corn rootworm insecticide was applied at planting? Yes. In corn following corn, many farmers want to control both corn rootworms and black cutworms with the same insecticide application. However, the at-planting insecticide may not give adequate control for a large black cutworm infestation, and a rescue treatment may still be needed.

What insecticides are recommended for rescue treatments? The following are recommended, with manufacturer label rates given in parentheses: Ambush 2EC (6.4 to 12.8 oz./acre), Asana XL (5.8 to 9.6 oz./acre), Lorsban 4E (2 to 4 pints/acre), and Pounce 3.2E (4 to 8 oz./acre). If the soil surface is dry, rotary hoeing just after application will increase the effectiveness of Lorsban. However, Ambush, Asana, and Pounce should not be incorporated.