R5 Corn Growth Stage and Scouting Tips

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R5 Corn Growth Stage

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R5 Stage* 
(Begins 35 - 42 days after silking.)

At R5, all or nearly all kernels are dented or denting. The shelled cob is dark red. The kernels are drying down from the top, where a small hard layer of starch is forming. This starch layer appears shortly after denting as a line across the back of the kernel (the non-embryo side). With maturity, the hard starch layer and line will advance toward the cob. Accumulated starch is hard above the line but still soft below the line.

  • Stress at this stage will reduce yields by reducing kernel weight.
  • At the beginning of R5, kernels have about 55% moisture content.


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

80 1,735
90 1,960
100 2,185
110 2,410
120 2,640
** Hybrid growth is influenced by the growing environment. Individual results may vary.

Scout for these Common Pests and Diseases Timing*
Anthracnose Top Dieback R3 through R5.
Anthracnose Stalk Rot R5 through R6.
Diplodia Ear Rot R5 through R6.
Diplodia Stalk Rot R5 through R6.
European Corn Borer Second-generation egg masses are laid in late-July through August.
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.
Western Bean Cutworm Scout ear tips for feeding.
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.