Identifying Corn Reproductive Stages and Management Implications

Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops July 14, 2021 17:35

Identifying Corn Reproductive Stages and Management Implications

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Corn reproductive stages may comprise nearly 60 days for full-season hybrids grown in Mississippi at normal planting dates depending upon seasonal temperatures. Corn maturation is closely correlated to temperatures and heat unit accumulation, so references to days between development stages may vary slightly depending on seasonal temperatures and planting date. Of course, early maturing hybrids (~110 day RM) will progress through reproductive stages slightly faster than our 118-120 day late maturing hybrids.

There are six commonly recognized corn growth stages noted with an R for reproductive growth, followed by a numeral designating subsequent stages.

R1: Silking

R2: Blister

R3: Milk

R4: Dough

R5: Dent

R6: Physiological Maturity

 

R1 Silking

Silking is defined when silks emerge from the ear to receive pollen and begin the fertilization process. Tasseling immediately precedes this growth stage, but essentially must coincide for successful pollination to occur. Corn is extremely sensitive to any stress which limits photosynthetic capacity at this time. This is because the kernels have very little ability to draw energy reserves from storage, because they are exceptionally small. The pollination process typically occurs in a relatively short (5-8 day) period. Each ovule has a silk attached which grows outside the husk at the ear tip to receive pollen in order to fertilize a kernel. After successful fertilization, silks will detach from the ovule and dry and turn brown. Corn’s is very sensitive to stress during the 20 day period from silking to milk stage and this affects kernel number.

R2 Blister

Blister stage occurs after pollination, as white kernels begin to expand, but have not yet attained the plump appearance of milk stage kernels. After successful fertilization occurs and kernels begin to develop, silks dry out and turn brown during this stage. Thus, this stage is also often referred to as “brown silk.” This stage comprises a period centered about 10 days after silking.

R3 Milk

Milk stage (or commonly referred to as roasting ear) occurs about 15 to 21 days after silking as kernels develop a buttery yellow color and are full of milky white fluid. The cob will remain practically white through milk stage. Stress from pollination through milk stage will readily cause kernels near the ear tip to abort, as energy is prioritized to the base of the ear. Ear kernel number is essentially determined by the conclusion of milk stage. Later, kernels progress through the dough stage, when kernels gain consistency and size, but remain soft and very moist.

R4 Dough

During a period about 22 to 28 days after silking, kernels transition through the dough stage, when kernels gain consistency and size, but remain soft and very moist. During the dough stage kernels gain consistency and the cob will attain a light pink color. Dough kernels will actually begin forming dents during latter stages, but remain a dull, matte appearance. Corn’s sensitivity to stress during the milk and dough stages is high and primarily affects kernel weight.

R5 Dent

Dent stage occurs around 30 days after silking when practically all kernels are fully dented and hard starch begins forming at the crown of kernels. Although it seems simple, accurate identification of this stage can be confusing, but is very important for irrigation scheduling and termination. The best way to accurately identify dent stage is when the kernel crown turns the bright, shiny, dark yellow color of mature kernels and obtain a firm consistency, indicating the onset of hard starch development. Many kernels begin forming dents during late dough stage or R4, but full dent does not occur until hard starch forms at the top or crown of the kernel. Kernels mature from the outside-in (toward the cob) when hard starch begins developing at the crown. Kernels will fill about 50% of their potential weight and develop for about 24 or 25 days, if stress does not hasten maturity. Thus, this is far too early to terminate irrigation, as yield will suffer if hot, dry weather prevails. Early irrigation termination may also deteriorate stalk strength and promote lodging, because plants will cannibalize energy from vegetative organs to fill kernels. Corn’s sensitivity to stress during this period is generally moderate, but it becomes considerably more tolerant as it approaches physiological maturity.

R6 Physiological Maturity

Physiological maturity is when kernel development is finished and “the crop is made.” It normally occurs about 24 to 25 days after dent stage in our environment. It is often identified by a “black layer” which develops when hard starch progression to the base is complete and the kernel is physiologically mature. Grain weight accumulation and development is complete at this stage. Vegetation and stalks will quickly die if hot, dry weather persists. Further management practices, including irrigation, crop defoliation by a harvest aid, etc… have no effect on kernels or grain moisture content after this stage.

 

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Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops July 14, 2021 17:35
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