European corn borer usually is not a serious pest of wheat. During recent years, it has been noticed more frequently in winter wheat growing in the eastern United States from New York to Georgia. Wheat is infested early in the season by the earliest emerging moths. In some areas where both pheromone types occur, preliminary research indicates that most larvae infesting wheat stems are the E pheromone type. In some locations, moths use wheat as an action site as well as a host on which to lay eggs.

Figure 47. Wheat damage by European corn borer. One stem has frass at the first node below the white head and the adjacent right rear stem has frass but is bearing a normal-colored head (J. W. Van Duyn).

Larvae bore into the stem at a node, usually the first one below the head on the main stem. A larva infests an average of two stems during its development by moving to a new stem before the last instar. Larvae cause the most severe damage when they bore enough into the stem to severely damage conductive tissues, which turns the wheat head white (Figure 47). Less apparent damage occurs when larvae feed upon leaves and stems but the heads remain normal in color (also in Figure 47). Weakened stems will lodge in heavy wind and rain, resulting in some heads being lost at harvest. The increasing incidence of this pest in wheat suggests that the European corn borer may become a more prominent problem on this crop in the future, especially with the planting of larger-stemmed varieties, the use of stripper-header combines, and reduced tillage practices.

The amount of economic loss in wheat caused by the European corn borer is not well known. Extreme infestations in New York have caused more than 40 percent of stems to be damaged (H. R. Willson). More research is needed to evaluate yield loss caused by European corn borer infestations, especially those caused by physiological effects on the different wheat varieties. Research in Georgia indicates that 10 percent or more of stems must be infested before control is justified (G. D. Buntin). No economic injury level thresholds for eggs and larvae have been established in wheat to date.