Corn reaches physiological maturity (black layer) at about 32% kernel moisture. Once physiological maturity has been reached, maximum yield has been achieved. However, corn at 32% kernel moisture does not harvest or store well, so growers wait until kernel moisture decreases. Corn stores well at around 15% kernel moisture, but at this moisture content harvest losses from the field (ear drop, lodging) and from the combine (header loss, shattering) can be significant. Field and combine losses are minimized when corn is about 24-25% kernel moisture. At this moisture content, kernels shell off the cob easily, stalk quality is generally good, and ears do not drop or shatter too easily during the harvest operation. Harvesting corn with kernel moisture in the low to mid 20’s reduces losses, but higher drying costs will be incurred compared to delaying harvest to allow additional field drying.
In years that experience some level of drought stress during the growing season, which will reduce late season stalk quality. All these factors suggest that harvest management this fall will be critical to minimize corn harvest losses.
Here are some key factors to keep in mind to reduce corn field and combine harvest losses and maximize profitability:
• Field and combine losses are minimized when corn kernel moisture is about 25%. Plan to begin harvest when kernel moisture is in the mid to low 20’s.
• Closely monitor stalk quality for every hybrid and every field. Quickly harvest any field where stalk quality is poor even though kernel moisture may be higher than you like.
• Drought stress reduces stalk quality and increases ear drop potential, so pay special attention to fields or areas with higher stress levels.
• Corn that is harvested can be managed, while corn in the field is continually vulnerable to losses due to weather events and other factors.
Assessing Stalk Quality
Weak stalks can be detected by pinching the stalk at the first or second elongated internode above the ground. If the stalk collapses, this indicates poor stalk quality, and stalks that are very vulnerable to lodging. Another technique you can use to assess stalk quality is to push the plant sideways about 8-12 inches at ear level. If the stalk crimps near the base or fails to return to the vertical position, poor stalk quality is indicated. Check 20 plants in several areas of the field. If more than 15-20 percent of the stalks are of poor quality, that field should be scheduled for early harvest.
Stalk Management Strategies:
1. Scout your fields to determine stalk quality: In 10 different places (choose both stressed and non-stressed areas) in the field do one of 2 tests:
a. The Push Test: Push 10 consecutive plants around ear height 12 inches off center and count the number of plants that don’t return to the erect position.
b. The Pinch Test: Pinch the lower 2 inter-nodes on 10 consecutive plants and count the number that collapse.
2. Based on the results, you may want to consider early harvest or it may provide insight on harvest order.
a. <20% = Wait a week and re-scout b. >20% = Candidate for early harvest
c. 50+% = Consider harvesting ASAP
4. Drying costs are going to be associated with early harvest. Fortunately we are early enough that there is opportunity to take advantage of warm ambient air temperatures in early October which changes the dynamics and costs of drying corn. Early harvest reduces harvest losses as well.
2013 environmental conditions that likely contributed to increase stalk lodging risk:
1. Good growing conditions in June and during pollination: When plants are determining kernel set V10 to V17, good growing conditions drive larger ears and more yield potential. Also good seed set during pollination to blister provides the draw of carbohydrates from the plant to the ear. Plants will cannibalize leaves and stalks to feed the ear.
2. Stresses in many locations but not all:
a. Solar Radiation – Cloudy conditions reduce photosynthetic efficiency
b. Drought – Currently much of the corn belt is in a moderate to severe drought
c. Nutrients – Above average rainfall early in the season resulted in significant losses of mobile nutrients like Nitrogen and Sulfur
d. Late Season Heat – In tandem with drought stress increases leaf firing and early plant death
e. Other possible contributors – Population, Overall Fertility, Insects, Diseases etc.