Corn planting is essentially complete across Ontario other then a small amount of replanting due to emergence/stand issues or where corn is following first cut alfalfa. Use the Replant Decision Aid posted at www.gocorn.net if considering this where stands are thin. Start with accurate plant counts of the current stand and consider all the replanting economics (crop insurance, seed costs, herbicide and equipment costs, etc). Corn leaf development requires ~75 CHU per leaf. Some areas came close to advancing by two full leaf stages over the last week. Weed control should be the priority as the crop moves through the critical 3-4 leaf stage. If applying UAN using streamer nozzles in the last half of May, use the full pre-plant nitrogen rate not the typically 10-20 % lower side-dress rate. Use the N Calculator at www.gocorn.net for rate selection. Warm dry weather conditions may increase the amount of soil N supply. Soil N testing (PSNT) may help fine tune side-dress N rates.