R1 Corn Growth Stage

R1 Stage: Silking*

This stage begins when silk is visible outside the husks. Pollination occurs when these moist silks catch falling pollen grains. Pollen takes about 24 hours to move down the silk to the ovule where fertilization occurs. The ovule becomes a kernel. Generally, all silks on an ear are pollinated in 2 to 3 days. The silks grow 1.0 to 1.5 inches each day until fertilized. The R1 kernel is almost engulfed in cob materials and is white on the outside. The inner material is clear with little fluid present.


  • The number of ovules fertilized is determined now. Those not fertilized will degenerate.
  • Environmental stress at this time can cause poor pollination and seed set. Moisture stress, in particular, affects the silks and pollen grains, which may result in a scattergrained ear or an ear with a barren tip.
  • Watch for corn rootworm beetles feeding on the silks and treat if silks are eaten to within 1/2 inch of husk.
  • At this point, potassium uptake is about complete. Nitrogen and phosphorus uptake is rapid. Nutrient content of the leaf correlates highly with final yield.

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

80 1,155
90 1,295
100 1,440
110 1,585
120 1,725

** Hybrid growth is influenced by the growing environment. Individual results may vary.

Scout for these Common Pests and Diseases Timing*
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.***
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.