Chad Lee, Grain Crops Extension
Plant and Soil Sciences, University of Kentucky
Corn planting in May will germinate, emerge, grow and develop in warmer temperatures compared to corn planted in April. Two critical stages of growth for early season management of corn are at growth stage V6 and V8. The growing point normally moves above ground on V6 corn (corn with six visible collars). If possible, N fertilizer should be applied by V8 (see related article in this newsletter). Many postemergence herbicide labels have applications restrictions for corn at either V6 or V8.
Based on data from the National Corn Handbook, corn should reach V6 in about 475 Growing Degree Days (GDD) and V8 in about 610 GDD. Using data from the University of Kentucky Ag Weather Center, over the last five years at Princeton, corn seeded on May 1 would have reached V6 and V8 about 9 and 12 days earlier, respectively, than corn seeded on April 1. Corn seeded on May 15 would have reached V6 and V8 about 13 and 16 days earlier, respectively, than corn seeded April 1.
As you plant corn late, and try to get soybeans planted as well, your postemergence herbicide applications and sidedressing of N fertilizer will need to occur earlier, relative to planting.
More information about late planting of corn is available in the Corn and Soybean Newsletter and on the Grain Crops Extension website at the Late Corn, 2009 page.