Crop & Pest Report


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Corn Development and Dry-down in 2018 (09/13/18)

For most of the state, corn growing degree days (GDDs) are running well ahead of normal.

Corn Development and Dry-down in 2018

For most of the state, corn growing degree days (GDDs) are running well ahead of normal. At some of our testing locations, hybrids with relative maturities recommended for that zone have already reach physiological maturity (black layer). In fact, some of the earlier maturing hybrids reach black layer around the first week of September. In terms of calendar days, this means that early-planted corn is maturing about two weeks ahead of normal (at least in many locations in North Dakota). When considering field drying, this is good new as the likelihood of having effective drying days is much greater for corn that matures earlier in the season. Though reaching black layer early increases the chances that the corn crop will dry quickly and require little if any on-farm drying, the rate of dry down will still be regulated by the weather in the weeks ahead.

A rough rule of thumb is that it will take at least a month to field dry corn, after reaching black layer, to the point that harvest can begin; probably less if the crop reached black layer in early September. However, the actual rate of drying is impacted by the moisture of the corn (wet corn dries faster than dry corn), and weather factors such as relative humidity, temperature, sunshine, rainfall and wind speed. It is possible for corn to lose up to 1% of grain moisture in a day when conditions are favorable, but typically, the highest rate of moisture loss one can expect is about 0.75% per day. Though temperature is not the only driver of moisture lost (one could not expect corn to dry at the same rate during a warm September day when it is raining as it would on a warm September day with low relative humidity), there are published reports that 30 GDDs are required for each percent of moisture lost. This relationship can be useful in roughly estimating the rate of dry down. For example, we might expect 6% moisture loss in the first two weeks of September when average GDD accumulations are 12.7 per day but less than 1% moisture loss the last two weeks of October when we on average accumulate only 1.3 GDD per day. The weather outlook for the next several days looks favorable for drying as temperatures will be above average. This will be followed by a period of more normal drying weather. Overall, it looks favorable for corn to dry reasonably fast this season. When planning your harvest, consider harvesting fields that have poorer stalk strength first to reduce the risk of losses due to lodging. Drought stressed fields are more likely to have poor stalk strength and late season drought stress was common in many parts of the state this year. For information on corn drying and storage, refer to the excellent NDSU Extension resources at


Joel Ransom

Extension Agronomist for Cereal Crops

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