Interpreting Black Light Data

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Black lights are established throughout North Carolina to monitor certain field crop pests. When used correctly, information gained from daily insect catches can improve pest management. Certain pest increases, intensity, and duration can provide critical information when paired with scouting and crop stage. In contrast, used incorrectly, the data can result in unwarranted insecticide application, damage to crops, and reduced profit.

To correctly interpret data, one must realize some critical points as follows:

• Intensity data (numbers of pest caught) from one light trap location should not be compared to another. Each light trap has a unique surrounding environment. Too, pests can be sporadic. As example, catches of corn earworm moths in Lenoir County often are much higher than the one in Craven County. This is not a reflection of a greater intensity of the corn earworm in Lenoir than Craven. Rather, the Lenoir County trap historically catches more moths.

• Some pest are attracted to the black light while others are not. Corn earworms are readily attracted to the light while Fall Armyworms are not. As such, be careful not to assume a low number of pest equates to a lack of problem within the field. Within Craven County as example, when 3-5 Fall Armyworms are caught in the light trap, this normally indicates a need for intense scouting in soybean, cotton and peanut crops. In other locations, this value may be the same, lower or higher.

• Historical data should be used for a specific light trap location as a measure of interpretation. Dates of peak catches normally move from South to North. However, exceptions occur. Most locations have a short history of catches available for review.

• An increase of any pest does not reflect a need to treat automatically. It signifies a need to scout more intensely. Often pest catches will increase yet the crop can tolerate insect feeding up until a critical threshold or crop stage. Too, adverse weather events may decrease pest survival rates.

• Do not make the assumptions that all pest will increase at the same time. Different pest emerge at different times.

• Some pest are simply not predicted by black light catches. Other methods may provide some indication of the emergence of these pest or one will simply have to rely upon scouting.

For more information, contact your local Cooperative Extension office or review black light data provided by NC State Extension.