Posted on July, 18, 2024 at 10:43 am
Ninth inning, two outs, bases loaded, pennant on the line. Your favorite team is up one run, with its best pitcher on the mound, facing the other team’s best hitter. Will he deliver the payoff pitch, a strike? OK, maybe growing corn isn’t quite as exciting as watching a dramatic baseball game. But if the growing season were a baseball game, the ninth inning is approaching. Will weather cooperate and deliver the payoff you want?
Mark Licht, Extension cropping specialist with Iowa State University, notes that what happens inside each ear from R1 through R6 determines your return on investment. “Grain fill and conditions during grain fill are crucial,” he says. “Ideally, you want as little stress on plants as possible.”
How does an ear of corn go from tiny blisters to mature kernels? In the following interview, Licht takes you inside corn development, a farmer’s version of inside baseball.
Cob diameter appears to grow as the ear grows — or is that an optical illusion? Yes, corncob diameter grows as the ear grows. Maximum ear girth occurs at about R5. Cob diameter reaches maximum size slightly earlier.
Does the cob provide a valuable function? Yes, the cob provides the mechanism for kernel attachment. It is also a conduit for water, carbohydrate and nutrient transport. These materials move from leaves to stalks to cobs to kernels.
Does the color of the cob matter? No. This is just a factor of the parental lineage of the hybrid. But since the same hybrid always has the same color of cob, it may be useful in confirming which hybrid was planted where within the field.
Does the cob play any role in drydown after black layer? No. After black layer development, there is no longer moisture movement out of the kernel through the cob. Kernel moisture loss after black layer is evaporative through the kernel pericarp and ear husks.
At what stage are kernels safe from frost? What happens if frost occurs at R4? Kernels are safe from frost at physiological maturity (R6), which is slightly before black layer. The earlier the frost, the greater yield loss as a result. Although after R4, there are fully viable embryos.
Can a grower do anything late in the season that will affect R4 and beyond? Not really. After pollination, it is all about protecting the factory, primarily the leaves, and reducing stress as much as possible. Unfortunately, stress is often weather related. Using foliar fungicide to hold back diseases is possible. But after R3, fungicides typically do not pay off.
If tar spot kills plants at R4 or R5, will kernels reach black layer? Anything that kills a corn plant before R4 to R5 stops kernel and seed fill. Those kernels will be smaller and lighter. Black layer as we know it will not develop. Harvesting for grain is still possible, but test weight will be much lower. Normal drydown, either naturally or heated, will not happen in the same way. It typically takes a bit longer and more energy to get the same percentage of drydown, and kernels are typically a bit wetter at R4 to R5 compared to normal.
Is there significance to knowing which side of the kernel is the embryo side, as shown in the diagram of cross sections of ears? Embryos are always on the same side in all kernels. The practical significance is gauging the milk-line progression as it moves from R5.25 to R5.5 to R5.75. The dent stage, R5, is the longest-duration grain filling stage. It would be easier for farmers harvesting corn silage or high-moisture corn to track the milk line by knowing where it shows up best.
Is the embryo side more prone to damage? There is no impact on mechanical damage, harvesting or drying.
The six key reproductive stages that take corn to maturity have letter designations and names.
“We also know about how long ears stay in each stage based on past research,” says Dan Quinn, Purdue Extension corn specialist. “It can vary somewhat based on temperatures and growing conditions.”
Quinn points to information inside the Purdue Corn and Soybean Field Guide that summarizes each stage:
R1, silking. Technically, silk emergence is the first recognized stage of the reproductive process, Quinn says.
R2, blister. Kernels are white on the outside, resembling a blister. This stage occurs 10 to 12 days after R1.
R3, milk. Kernels are yellow on the outside but milky white inside, 18 to 20 days after R1. Kernel moisture is about 80%.
R4, dough. Kernels reach this “pasty” stage 24 to 26 days after R1. Moisture at beginning R4 is about 70%.
R5, dent. This stage begins 31 to 33 days after R1 at 60% moisture, and lasts about 33 days, requiring around 200 growing degree days. The milk line moves slowly down the kernel, replaced by solid starch, Quinn notes.
R6, physiological maturity. The final stage occurs 55 to 65 days after R1. Quinn explains that R6 occurs slightly after the milk line disappears and just before the black layer forms.
Source: Farm Progress