Pheromone-baited traps can be used to monitor flights of corn earworm moths. Large, cone-shaped traps constructed of wire (Hartstack traps) or nylon should be baited with lures containing the sex attractant that is specific for male corn earworm moths.
When using nylon traps, note that these traps catch a third to half as many moths as the metal Hartstack traps. Place traps along edges of fields before and during the susceptible stage of the host crop: silking in corn, or the presence of pods and fruit in green beans and tomatoes, respectively.
Pheromone traps provide valuable but somewhat indefinite information about corn earworm populations. Fluctuations in counts from traps may be a result in changes of temperature or from rain and wind. Whenever a trap catches a few moths per night for two or three nights in a row, a “significant” moth flight is occurring.
However, precise predictions of crop damage based on counts of moths in traps is not possible. Because females have emerged before males and are ready to begin egg-laying as soon as they mate, the capture of male moths in traps means that eggs will be deposited on susceptible hosts within hours.
Both trap counts and scouting should be used in determining the optimal spray period. Scouting for eggs immediately after traps detect moths can help to indicate the potential for damage in a specific crop. When scouting for earworm eggs in corn, sample five areas of the field, 20 ears from each area (total of 100 ears). Clip silks from corn ear and place in plastic bag.
Examine the silks for eggs by separating over a black or dark colored surface. Also examine ears for larval damage. Grasping the ear, pull it open, and check for the presence or absence of earworm damage. Determine the percent of ears with damage. A rescue treatment may be required if 5 to 10% of the ears are infested with eggs or larvae.
If infestation levels are below the threshold, then it is advised to scout again in a couple of days. After scouting the field for a second time, if the cumulative infestation level (the infestation level from the first scouting plus the level from the second scouting) exceeds the threshold, an insecticide application may be recommended.
Producers sometimes use a threshold of 10 moths per trap per night for sweet corn grown for processing or 5 moths per trap per night for fresh-mark sweet corn. For seed corn, control is recommended if significant moth flights occur when fresh silks are present.
The interpretation of moth counts from traps is less clear-cut when pest management decisions focus on commercial production of snap beans or tomatoes. If tasseling and silking corn is abundant in the area, corn earworm moths will deposit the great majority of their eggs in the corn, not in beans or tomatoes.
In these instances, insecticide applications may be unnecessary in beans and tomatoes, even if pods or fruits are present. In corn, control may be necessary if earworm moth flights occur while fresh silks are present, but sprays are generally considered to be unnecessary after 90% of the silks have browned.
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