Thrips are most noticeable, and of greatest concern on corn at two periods during the growing season: on young seedling plants, and at ear formation. On seedling plants their feeding makes the plants look stunted. At ear formation, thrip injury to developing kernels provides entry for infection by Fusarium spp. and subsequent Fusarium ear rot disease.
Some may mistake this late season thrip damage as a disease issue. If you see this type of symptom in your field, contact your county extension agent for a positive diagnosis of thrip injury or foliar disease.
Treatment is usually not necessary on corn seedlings, because plants recover from thrip injury. Thrips are also beneficial at this time because of their role as mite predators. No threshold has been established for damage from thrips at ear formation. Treating for thrips will probably not prevent spread of Fusarium ear rot disease.