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Careful consideration should be given prior to switching to an earlier corn product. Full-season corn products for a given area typically have the highest yield potential, which can help offset an increase in drying costs. As planting is delayed, corn products actually reduce their GDD (growing degree day) needs. GDD accumulation increases as the the growing season progresses. As a result, the number of GDDs required from planting to physiological maturity (black layer) decreases by nearly 7 GDDs per day as planting is delayed beyond May 1st. This means that late-planted products mature in fewer than expected GDDs. Therefore, corn planted in May compared to an optimum planting date may require 125 to 200 GDDs less to reach black layer. Recommendations from your local agronomist regarding full-season corn relative maturity (RM) groups and RM switch dates for Minnesota are listed in Table 1.
The yield for late-planted corn will vary greatly depending on the rest of the growing season. The decision to switch maturity with delayed corn planting is difficult because of variations in growing seasons relative to available GDDs, the first frost date, and fall drying conditions.
Table 2 lists average accumulated GDDs, at several locations over several weeks, based on an April 28th planting date. This information can help with the decision of when to switch to an earlier maturity by determining the potential GDDs remaining from a given planting date to typical maturity or killing frost in a given area. Table 3 shows average first frost dates for some cities in Minnesota.
Corn with Monsanto traits that offer insect protection and herbicide tolerance, such as SmartStax®RIB Complete® for the Corn-Growing Area and Genuity®VT Triple PRO®RIB Complete®corn blends, should be considered. Additionally, even with delayed planting, it is still important to try to minimize the risk of adverse weather during critical growth stages by planting a package of products that range in GDD requirements to flowering as well as maturity.