Several articles have appeared in the ICM News describing the effects of recent weather on corn, including temperature effects on corn emergence,hard freeze effects on emerged corn, and corn tolerance to herbicides. Another issue involves determining the correct growth stage of corn that was damaged by the May 9 frost event. Herbicide labels typically restrict application either by corn height or leaf number. Leaf number is considered more accurate than height since it better represents the physiological stage of corn development (although this is muddied since people count leaves differently and it isn’t always clear on herbicide labels which counting method is used). See pages 4 to 9 in the Corn Field Guide for information on the leaf-collar corn staging system.
Iowa State University
Hartzler, Robert G., "Postemergence Herbicides on Frost-Damaged Corn" (2010). Integrated Crop Management News. 440.