Damage Larval mines can usually be diagnosed through their comma-like appearance. Twenty five to fifty percent of the leaflets may be mined during heavy infestations and this could result in loss of quality. Yield loss is not expected unless significant leaf drop occurs. This type of damage is usually not considered a plant health problem. Scouting and Damage Threshold Decisions to treat must be made during the adult pinhole feeding stage.
Scout fields on a weekly basic to determine the percentage of leaves with pinhole feeding.
The need for chemical control is difficult to determine. Economic benefits will only be obtained if leaf drop occurs or if a high percentage of the leaflets show excessive feeding. Early cutting can be used to reduce damage and would be most beneficial during first cut. Subsequent cuttings may not coincide with peak larval damage. Research is being planned to introduce this same parasite into the upper Midwest.