R6 Corn Growth Stage and Scouting Tips

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R6 Corn Growth Stage - Physiological Maturity

R6 Stage: Physiological Maturity* 
(Begins 55 - 65 days after silking.)

By the R6 stage, kernels have attained their maximum dry weight or dry matter accumulation. The hard starch layer has advanced completely to the cob. A black or brown abscission layer forms, moving progressively from the tip ear kernels to the basal kernels of the ear. It's a good indication of physiological maturity and signals the end of kernel growth. The husks and many leaves are no longer green, although the stalk may be.


  • A hard early frost before the R6 stage may halt dry matter accumulation and cause premature black layer formation. This could reduce yields by causing delays in harvest (frost-damaged corn is slower to dry.)
  • To reduce potential frost problems, choose a hybrid that matures about 3 weeks before the average date of the first killing frost.
  • Kernel moisture averages 30 to 35%, but this can vary considerably between hybrids and environmental conditions. Safe storage requires 13 to 15% moisture.

GDUs Required** to reach R1 growth stage depends on maturity and is approximately:

80 1,895
90 2,145
100 2,390
110 2,640
120 2,890
** Hybrid growth is influenced by the growing environment. Individual results may vary.

Scout for these Common Pests and Diseases Timing*
Anthracnose Stalk Rot R5 through R6.
Diplodia Ear Rot R5 through R6.
Diplodia Stalk Rot R5 through R6.
Fusarium Ear Rot R5 through R6.
Fusarium Stalk Rot R5 through R6.
Gibberella Ear Rot R5 through R6.
Gibberella Stalk Rot R5 through R6.
Stewart's Wilt Disease is initiated with corn flea beetle feeding from VE to V5. Leaf symptoms appear after R1.

Click on the insect or disease for more information.

* Information from Pioneer and Iowa State University Extension.

Use this information as a guide and it should not be the only factor in making decisions.