- Even with the cool start of the season, most corn acres across the territory are in the mid to late reproductive stages of development.
- Adequate temperatures and moisture throughout the rest of the season will help the crop reach maturity before the average first frost date.
- Regardless, now is a good time to reach out at the beginning of the Great Lakes Grain Crop Assessment tour and have your fields assessed for yield
With corn acres at or approaching the late reproductive stages, it is now a good time to review these stages briefly.
Dent Stage (R5) – Under optimum growing conditions, corn will normally start to develop depressions or dents in the kernel crowns about four to six weeks after silking. This is the “dent stage” (R5) and signals a rapid starch accumulation in the kernels. At this point, and for the next 20 days or so, a distinct line begins to form, starting at the crown of the kernel and progressively moving toward the tip. This is referred to as the kernel milk line. The milk line marks the division between the starchy part of the kernel and the softer, milky part of the kernel (Figure 1). Literature indicates that total plant death at the beginning of the dent stage will reduce final yield about 40 percent. Total plant death at about half milk line will reduce yields about 12 percent. Note: Milk line in kernels is often used to schedule corn harvest for silage.
Physiological Maturity (R6) – Maximum accumulation of starch in the corn kernel marks physiological maturity, which normally occurs 8 or 9 weeks following silking. Black layer formation at the tip of the kernel follows rapidly (Figure 2). At this point, the corn is more-or-less safe from frost or other stress factors, although physical damage can still greatly impact yields. Grain moisture at R6 usually will range from 25 to 40 percent. If the plant is still healthy, it will actively draw moisture from the ear and harvest moisture will be reached more rapidly. Once corn has reached R6, roughly 0.5-0.75% moisture can be drawn out of the kernels per day. Issues with plant health, stalk damage, disease, poor weather, or other serious problems will slow the physiological removal of moisture from the ear and the grain will have to “air dry”.
Image 2. Black layer formation in corn kernel
In Ontario our CHU are 4 to 5 days ahead of last year but 2 to 3 days behind the 30 yr long term average. With the warms days we all think we should be ahead. We stop calculating CHU when day time temperatures exceed 30C . We need 40 more days to get to black layer, placing most corn maturing in the last week of September to middle of October.
A normal year.