The reproductive stages of corn are often over looked and not fully understood, but as discussions of fungicide applications, maximizing yield and monitoring grain development continue, having a basic understanding will help make better production decisions:
Corn reproductive stages generally consume 60 days starting with silk emergence and ending at black layer. There are six recognized growth stages during the reproductive stages and are designated with an “R,” followed by a number designating subsequent stages.
R6: Physiological Maturity
Silking (R1) begins when silks emerge from the ear and are ready to receive pollen.
Blister (R2) stage begins 10 to 14 days after silking begins and the kernels are whitish blisters and contain a clear liquid if busted. By this point the silks are brown and drying rapidly. R2 is also often referred to as the “Brown Silk Stage.” Starch begins to accumulate in the kernel while the radicle root, coleoptile and first leaf have formed in the embryo.
Milk (R3) stage begins 18 – 22 days after silking. R3 is commonly referred to as the roasting ear stage. The kernels are mostly yellow or dull yellow and filled with milky white fluid. By the R3 stage the ear kernel number is generally determined and additional kernel loss will be minimal.
Dough (R4) stage begins 24 – 28 days after silking. The kernel’s milky fluid is changing to a “dough” consistency as starch accumulation. The kernels are gaining consistency and size and the color is becoming more yellow and could develop a small dent in the kernel. Stress during this period will not lead to kernel loss, but will primarily affect the kernel weight. The cob is beginning to show some color from light red to pink.
Dent (R5) occurs 35 – 42 days after silking and all kernels have fully dented and the hard starch begins forming at the top of the kernel. The best way to recognize and identify this stage is to look for the top of the kernel turning bright, shinny, dark yellow color and the inside of the kernel is of a firm consistency. Kernels will continue to fill and add weight for another 20 days and hot dry weather can still reduce yields by 15-20% during this stage.
Dent stage also is when the “milk line” can be seen. The milk line is the separation between the liquid and solid starch areas of the kernel. As the kernel continues toward maturation the milk line moves from the tip to the top of the kernel.
Physiological Maturity (R6) starts 55 to 65 days after silking and is often referred to as “black layer.” Physiological maturity occurs shortly after the milk line disappears and just before the formation of the black layer at the tip of the kernel.