The damage to wheat caused by this springs’ cold temperatures has many producers planning to replace their wheat crop with corn. While this may be a good agronomic alternative, it brings with it concerns for controlling insect pests. Two particularly important pests are (true) armyworm and black cutworm.

Both insect pests are common and both can occur in corn. In addition, both may occur at increased levels in corn planted into standing wheat but for different reasons. Both are “grass loving” insects; that is they can live and reproduce on grasses and may choose this type of plant in preference to others.

Why has the risk increased? With armyworms this is pretty simple, they are primary pests of wheat. They are not often a problem because they are usually controlled by their natural enemies to a level below the economic threshold. However, one must understand that there are many more wheat plants in an acre than there are corn plants. For example a wheat crop planted to achieve 30 plants per square foot would have about 1.3 million plans per acre. Comparing this to a corn population of 28 thousand plants per acre is a difference of near 50:1! So, an insect population that would cause minor damage to wheat may cause significant damage to corn.

So far in this 2007 the UK-IPM pheromone traps have indicated a higher than normal numbers of black cutworm and armyworm moths.

Click here to see these graphs»

It is too early to know if this will remain the case. Certainly the counts over the last two weeks have been lower but this may simply be because of very low daily temperatures and very high winds. One can not yet tell if the insect populations have been damaged by the cold.

We think that the insects that have hatched into worms in the field are unlikely to be much of a problem for the corn. By the time the corn emerges those insects will have died or completed their development. What is as yet unknown is how far into the spring egg lay we have proceeded. With armyworm we can say with some confidence that barring damage to the insects by cold, we can expect that the majority of the eggs have not yet been laid.

Estimation for black cutworm is more difficult. This insect does not produce distinct generations. But our guess is that like the armyworm, the bulk of the eggs have yet to be laid.

Listed below are some items that can help you reduce the risk your corn planted into dieing wheat will face from these insect pests.

Choose your Corn Varieties Carefully:

Some of the Bt corn events have good suppression of black cutworm, others do not. Seed treatments also have some suppression of cutworms but levels may vary to some extent on the level of seed treatment. But one fact remains, depending on the level of cutworm and armyworm activity, preventive treatments may not provide sufficient control of these pests. We strongly suggest that these fields be monitored regularly until the field reaches 12 to 18 inches in height.

Before Corn Planting / Emergence:

• If possible remove the bulk of the wheat plant for some other use (example – hay, wheatlage WARNING: Samples should be tested for safety to animals).
• Use a herbicide that kills the wheat quickly,
• Leave as much time as possible between the killing of the wheat and the emergence of the corn.
• “Pre- or At-’” plant insecticides are unlikely to provide complete protection because of the length of time the insects will be present.
• These two insect pests may be in the field together, depending upon the state of the dying wheat tissue.
• Decaying organic matter will provide the armyworm and cutworms a place to hide from natural enemies, and protect the insects from pesticides.

Once the corn is up:

• Scout fields with standing green / yellow wheat first for the presence of armyworm,
• Scout fields with heavy loads of dead wheat tissue first for cutworms.
• Apply insecticides as needed. Ensure that good coverage of the corn plant is obtained, both insects will hide in the organic matter.

For information about corn pests, visit Insect Management Recommendations.

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