Corn kernels are about 32% to 30% moisture content at physiological maturity or when black layer develops. Several factors influence field drydown after black layer. Kernel moisture content decreases faster with warm, dry weather and may decrease slowly in a wet and cool environment. Fuller season corn hybrids that require more growing degree units (GDUs) to mature will likely be slower drying as the fall progresses within an area. A full season Hybrid like DKC64-87RIB requires about 2,850 GDU’s to reach black layer. Crop maturity can be delayed by dry weather, which usually results in a loss of potential yield because plant death occurs before the kernels gain their full weight and size.
Did you know that the optimum grain moisture for grain corn harvest is 23% to 25% moisture? Typical drying rates after black layer range from 0.4% to 0.8% kernel moisture content loss per day. I like to use the guide of about 3 days are needed to remove 1 point of grain moisture from the kernel. Therefore, we need about 21 days to get from black layer to 25% grain moisture. Most of the corn in my area pollinated July 24 to 30. Black layer was predicted to be Sept. 28 to Oct. 1.
In addition, corn hybrids differ from one another in drydown rates. Plant characteristics that can influence drydown rate include:
• Genetics. Some hybrids are engineered to dry very fast regardless of their maturity.
• Husk leaf number and thickness. Fewer husk leaves and thinner leaves can lead to faster moisture loss.
• Husk dieback. Some hybrids have husk leaves that turn brown or die very early compared to the rest of the plant. This can lead to more rapid grain drydown.
• Ear tip exposure. Exposed ear tips may provide for quicker grain moisture loss.
• Husk tightness. Husks that are loose and open tend to dry faster.
• Ear angle. Upright ears can capture moisture from rainfall and dew. Ears that hang down early dry faster.
• Kernel pericarp properties. Some hybrids have a thin pericarp which is the outer layer covering a corn kernel and these hybrids tend to dry faster.
Late planting and cool weather effects
Late planted corn can result in taller plants and smaller diameter stalks because the plants are developing in warmer temperatures and longer days than in very early spring. Plants also pollinate later when temperatures are hotter and maturity is delayed from later planting time. Delayed maturity can also result in a less than desirable grain moisture content well into the harvest season. The good news is that most corn hybrids shorten their GDU’s to black layer by 200 GDUs when planted late. This translates into about a full week shorter to complete their life cycle.
Cooler fall temperatures decrease the rate that kernels lose moisture content. More importantly, an early frost can be a threat for late-planted corn or timely planted corn that experienced a cooler than expected growing season. A cool growing season in combination with late planting in some parts of the United States can push maturation into potential frost timeframes. The good news is that we have been tracking normal or ahead of normal in Ohio for GDU accumulation and rainfall. We have had a good growing season but a later than normal planting timeframe.
A killing frost can occur when air temperature drops to 32 degrees F for four to five hours, or when it drops to 28 degrees F for only 5 to 10 minutes. This sub-freezing temperature can kill the entire corn plant or severely damage leaves, stalk, ear shank, and husks. A light frost can occur when air temperature is 30 to 32 degrees F for an hour or two, which could kill corn leaves, but not the stalk. The corn stalk is a temporary storage organ for nutrients that could move into the corn kernels. Grain yield can continue to increase after a light frost that only kills the leaves. The temperature and time of exposure can influence the degree of damage to the corn plant.
The early dent stage is generally considered the cut-off point where corn can withstand frost damage to the leaves and still produce a reasonable grain yield. Early dent stage is when kernels are showing small indentations, at least in the lower half of the ear. Frost damage can be more severe when it occurs on corn prior to the dent stage. A frost at the growth stage of half milk line can reduce yields by 5% to 10%. Potential yield losses are generally negligible if frost occurs when grain moisture is below 35%.
As always, keep safety at the top of mind during harvest. I wish you a successful harvest.