Corn planting was delayed until early to mid-June in areas across the Corn Belt. As a result, corn pollination occurred two to three weeks later than normal, and crop maturity is lagging by a similar time span. This presents the question as to whether freezing temperatures could occur before crop maturity.

Although detrimental, the first freeze may have limited yield and grain quality consequences in most cases according to DuPont Pioneer agronomists. Often a first frost will be light enough to affect only corn leaves, allowing the plant to continue to fill grain from stalk carbohydrate reserves. A worst-case scenario would be a hard freeze of 32 degrees or lower for several hours. If this occurs prior to crop maturity, it could bring a more abrupt end to corn development and, consequently, result in possible yield and test weight reductions and slower grain drydown. To estimate percent yield loss, you will need to determine the ear development stage at the time of freeze.

Rather than looking at GDUs now, breaking a few ears and looking for the location of the milk line once it begins to progress downward will give you a good determination of maturity. The milk line is the line separating the starchy area from the milky endosperm. It moves down from the crown of the kernel, at about 1/4 of the length of the kernel per week, to where it attaches to the cob. An ear with most kernels at half milk line will be about two weeks from black layer.

You may find that you will have wet or immature corn in October, making your decision on when to start combining difficult. Experience gained during several years of late harvest suggests that excessive delay may not be a good idea for the following reasons:

• A delayed start means a delayed finish, resulting in less time available for harvest as well as fertilization and tillage.
• Limited fall tillage and fertilization may reduce options for crop rotation next spring.
• Drying corn with ambient temperatures in the 20’s requires more energy than drying corn with ambient temperatures in the 40’s.
• Heightened safety concerns and potential for increased damage to machinery when working with frozen soils and snow or ice-covered roads.