The larva damages the crop by entering the stem and destroying the pith, xylem, and phloem. Damaged plants are susceptible to wind damage, water stress, and invasion from pathogens such as blackleg. The impact of the European corn borer on the potato plant appears to be a function of larval numbers, phenological stage of the plant at the time of attach, the cultivar, presence of other insect pests and diseases, and other stress factors such as temperature, water, and fertility. Because the young larvae are present on the foliage for only a few days the window for control with a bacterial or synthetic insecticide is quite small. Insecticides are no longer effective after the larva has entered the stem.
At present, no thresholds exist for control of the European corn borer on potatoes. However, data from Prince Edward Island indicated that 1.2 larvae/stalk/week reduced yields of Russet Burbank by a margin of 8-9%. Monitoring for this pest is best accomplished with water pan traps baited with the "Iowa" strain pheromone. The trap should be located in a grassy area adjacent to potato fields and checked frequently for adult males. When males are detected the field should be monitored for egg masses. Any applications of insecticides, if required, should be timed to control newly hatched larvae before they enter the plant's stem.