R4 Corn Growth Stage and Scouting Tips

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R4 Corn Growth Stage - Dough

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R4 Stage: Dough*
(Begins 24 - 28 days after silking.)

Continued starch accumulation in the endosperm causes the milky inner fluid to thicken to a pasty consistency. Usually 4 embryonic leaves have formed as the embryo has grown dramatically from the R3 stage. The shelled cob is a light red to pink. Toward the middle of R4, the embryo will stretch across more than half of the width of the kernel side. Just before R5, kernels along the length of the ear begin to dent or dry. The fifth (last) embryonic leaf and the lateral seminal roots have formed. If this seed is planted, these 5 embryonic leaves will appear the following season after germination and VE.


  • The embryo continues to develop very rapidly.
  • Kernels are about 70% moisture and have accumulated about half their mature dryweight.

GDUs Required** to reach R4 growth stage depends on maturity and is approximately:

80 1,570
90 1,775
100 1,980
110 2,180
120 2,385
** 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.
Common Rust V12 through R4.***
Corn Rootworm Larval feeding is most extensive in early through mid-July in most regions of the Corn Belt.
European Corn Borer As the true stalk develops and European corn borer larvae increase in size, larvae can be found tunneling into the stalk.
Eyespot V6 through R4. Disease primarily found in northern environments.
Goss's Wilt VE through R6. Disease primarily found in Nebraska and portions of other western states.
Gray Leaf Spot VT through R4.***
Northern Leaf Blight VT through R4.***
Southern Leaf Blight VT through R4.***
Stewart's Wilt Disease is initiated with corn flea beetle feeding from VE to V5. Leaf symptoms appear after R1.
Western Bean Cutworm Initiate scouting based on local pheromone trap captures of adults. If trap data are unavailable, begin scouting at VT.

Click on the insect or disease for more information.

* Information from Pioneer and Iowa State University Extension.

*** Scout for these diseases earlier in seed production fields.

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