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Farmers need to evaluate if crop damage or loss related to field drying is less than the cost of drying. The breakeven point between total drying cost versus value of lost yield due to field drying depends on several factors: ear and stalk health, crop maturity, weather forecast, and drying costs. Many times, farmers can afford greater drying costs as corn prices increase. Farmers may also need to plan for propane and drying space when the value of yield loss during field drying is expected to be greater than the cost of drying.
Ear retention can be a concern especially when ears hold a lot of grain. Storms can cause ears to drop to the soil, and ears in a downward position may be shelled in corn heads during combining. Both can lead to volunteer corn issues next season. Farmers should also be aware of ear rots such as Gibberella that can produce mycotoxins. Grain infected with Gibberella should be dried to 15% moisture content to help reduce the risk for mycotoxin accumulation.1
According to a study in Ohio, stalk rot incidence increased between harvest dates in October and November.2 In the same study, stalk lodging was observed to have the greatest increase after mid-November. Mid-November was also the time period when 90% of the yield loss related to delayed harvest occurred.
Corn product maturity mostly affects the amount of time plants spend in the vegetative stages.3 At harvest, corn products that have a one “day65533;? difference in relative maturity may vary by a percentage point of grain moisture content, even if they were planted on the same day. The timing of corn maturation influences the field drydown rate; with corn maturing in late August having a dry down rate of 0.8 percentage points per day.4 Corn maturing mid- to late-September would have a drydown rate of approximately 0.4 percentage points per day.
The rate mature kernels field dry depends on temperature, humidity, and rainfall. Table 1 lists typical drydown rates during favorable weather. However, after mid-November field drydown is expected to be negligible. Corn grain moisture content in Ohio was shown to have only a 0.5% point decrease after early to mid-November.2
Growing degree days (GDDs) can be used to estimate drydown rates. It may take approximately 30 GDDs to reduce each percentage point of grain moisture content between 30% (maturity or black layer) down to 25% moisture content.5 Grain dries at a rate of one moisture point per 45 GDDs between 25% and 20% moisture content. GDD accumulation is not typically adequate for significant drydown in November. For example, November GDD accumulation for Ohio was only 19 GDDs in 2012.6
As weather becomes cooler, a greater concern may be frost damage. Frost-damaged grain goes out of condition quickly. Farmers will need to plan for additional propane and bins for artificial drying when frost is forecasted with high moisture content grain in the field.
Stalk and ear health deterioration contribute to greater yield loss during later harvest weeks. The potential for grain loss, along with negligible loss of grain moisture content, drives the need to harvest as soon as field conditions allow.