Important Corn Pest Information

This spring Penn State Extension in Franklin County set up a network of eight sites to monitor populations of black cutworm moths and true armyworm moths. One of these sites was in the St. Thomas area. This trap received significant flights of both black cutworm moths and armyworm moths. These numbers raise the risk of damage by these pests, please read the following statements for management considerations.

The most important step for you to take at this time is increase your level of observation and scouting in your corn fields. The distribution of these pests can be very spotty, so it is often the case that very few acres are infested and will need to be treated with insecticides. Specific information pertaining to scouting, economic thresholds and life cycles are important to understand and consider. Initial scouting for these pests involves moth trapping, which indicates a possibility of local populations of caterpillars developing. Unfortunately, higher local populations of moths does not always lead to damaging populations of caterpillar, but the correspondence is strong enough to warrant a warning of potential damage to growers in the vicinity..

Black cutworm moth:

Cutting behavior of black cutworm caterpillars is expected 300 growing degree days after the significant flight. The Penn State Agronomy program in Franklin County has recently established a weather station in Chambersburg Pa and has been tracking growing degree days since the significant flight occurred. The threshold was reached on Sunday 5/23/2010. Now is the time to start scouting corn fields to look for cutting damage. Economic thresholds for treatment are 2, 3, 5, and 7 cut plants per 100 for seedling, V2, V3, and V4 respectively.

Treatment options for at-risk areas vary but can include higher rates of neonicotinoid seed treatments where corn has not been planted and planting lines of Bt corn with activity against black cutworm if seed is still needed; however, growers should recognize that neither of these options are completely effective. The most economical control method for cutworm is scouting fields and applying rescue treatments where cutting activity exceeds economic thresholds.

More information on this pest can be found online at http://ento.psu.edu/extension/factsheets/black-cutworm , or by visiting the local extension office.

True armyworm moth:

One of the most important management considerations when dealing with true armyworm is to make sure in areas where you have cover crops or heavy weed cover that you allow a 2 week period after the plants are dead until you plant. This would lead producers trying to get a timely planting of corn who have yet to spray to use a quick killing herbicide such as gramoxone instead of glyphosate.

Once corn is established scout fields closely, especially where heavy cover was. If you find more than 10 percent of your corn in a given field has an infestation of armyworms treatment is encouraged. Armyworms typically are found hiding in the whorl of corn during the day and their feeding creates a ragged looking leaf. In bad cases the leaves will be fed on until nothing but the mid-rib is left.

More information on this pest can be found online at http://ento.psu.edu/extension/factsheets/armyworm, or by visiting the local extension office.

Finally, I would ask that you share this with other farmers in your area who may not receive Agronomy Notes. The greater the awareness of this issue, the less likely we will have economic losses due to these pests. As always, if you have any questions or need hard copies of the fact sheets mentioned above feel free to contact me at the extension office 717-263-9226 ext. 227. I am often away from my desk but check messages frequently.