Most cornfields are likely at or near black layer by now. Dave Nanda says it’s easy to determine if black layer has occurred. Simply pull an ear, pull back husks, break the ear in half and examine a few kernels, using a pocketknife.
“You should find a thin, black to brown layer of cells at the tip if the black layer formed,” says Nanda, director of genetics for Seed Genetics Direct, the company that sponsors Corn Watch ’21. “Black layer means corn has reached physiological maturity, and no more materials can enter or leave the kernel.”
Moisture content is often around 30% at black layer, but it can range from 25% to 40%, depending upon the hybrid and field conditions.
“The next question is when to harvest,” Nanda says. “Many factors come into play, including how many acres you have to harvest, whether you’re drying yourself to selling out of the field, and some traits of the hybrid. Some kernels may have a thinner pericarp, or skin, and dry down quicker than others.
“However, there’s no doubt that the 800-pound gorilla in determining drydown for corn left standing in the field is weather. Warm, sunny days in late September and running into October will remove several points in a few weeks. Conversely, if it’s cool and wet, drying won’t go as quickly.”
Key harvest timing considerations
Nanda suggests considering these factors when deciding how long to let corn stand:
Weather outlook. Pay attention to long-range weather forecasts. If there are warm, dry periods ahead, it may provide an opportunity to cash in on some free natural drying. However, if wet, stormy weather is in the offing, there are two negatives. Corn doesn’t dry as fast, and storms bring the possibility of strong winds that can cause lodging and higher yield losses.
Health of plants. Are plants still green and healthy, or did dry weather stress take its toll? Are they fading fast?
Specific stalk rots. Anthracnose is one of the most common stalk rots today. Black specks and a shoe polish-type finish appears on the outer stalk, with the pith inside turning dark. Other stalk rots can also invade. Do a push test or pinch test on 100 stalks in a row at a few places at random to see if stalks still have integrity. Mark fields for quick harvest if too many stalks fail this test.
Premature ear drop. This may be more of a problem in non-GMO corn or hybrids without aboveground insect protection. European corn borer is one of the culprits that can invade and weaken the shank. If ears start falling on the ground, yield drops quickly.
Point of diminishing returns. At some point, usually in late October to early November, natural drying in the field becomes so slow that the risk of leaving the crop another day and risking a storm that could cause lodging outweighs any benefit from extra in-field drying, Nanda says.