Corn planting is 95 % complete across the province. Emergence is good to excellent in most areas with the majority of the corn in the 1-3 leaf stage. Weed control should be the priority as the crop approaches the critical 3-4 leaf stage. Cutworm injury has been reported in some areas south of London. Scout fields that had significant weed growth before planting. General guidelines for post-emerge UAN application are:
- UAN (fan nozzle) and herbicide – max. 2 leaf corn,
- UAN (fan nozzle) no herbicide – max. 3 leaf corn,
- UAN (streamer nozzle) – max. 6 leaf corn.
However, the herbicide manufacturer should always be contacted first to determine whether or not they support a post emergence UAN application with their herbicide.
Loss of N through volatilization will be greater if surface applied UAN does not receive rainfall to incorporate into the soil. Possible strategies are:
- delay application until rainfall is more likely,
- apply additional N (15%) to compensate for losses,
- add a urease inhibitor (i.e. Agrotain) to reduce volatilization losses or
- switch application strategies to sidedress injection.