Predicting Corn Crop Maturity

There have been pockets of too little rain and areas with more moisture than desired. The temps have ranged from cool to blazing, and the maturity levels of the east-central Minnesota and western Wisconsin corn crops vary by geography.
 
Even late-planted fields are dented (R5) and earlier plantings are quickly moving toward R6; last week’s higher temperatures sped up the process.
 
It’s possible to predict when your corn crop will be at black layer and ready for harvest. Craig Loen, Federated agronomist at the Osceola location, offered this outline of the various stages of corn reproduction and pointed out that with the date of tasseling (VT) you can track the predict crop maturity, noting stresses, temps, and moisture conditions that affect corn ear development.
 

• VT—Tasseling, approximately 75-84 days (or 1100-1400 GDUs) after planting.
• R1—Silking, 2-3 days after tasseling; silks continue to grow (after sundown) for up to 10 days after silks emerge; it is typically 55-60 days to maturity from silking.
  • Many factors determine successful pollination, but adequate moisture and temperatures that aren’t too high are especially important for good pollination.
• R2—Blister stage, when white blister-shaped kernels appear on cob with clear fluid in kernel. Severe stress on the plant can lead to aborting kernels; 10-14 days after silking, 45-50 days to maturity, high kernel moisture at 85%.
• R3—Milk stage, when kernels turn yellow, with a milky looking fluid in kernel; 18-22 days after silking, 37-43 days to maturity, 80% kernel moisture.
• R4—Dough stage, when starch accumulation increases, fluid in kernel starts to thicken and become doughy; 24-28 days after silk, 31-37 days to maturity, 70% kernel moisture.
• R5—Early dent stage, when almost all kernel crowns are dented, milk line starts to move down, separating the milky liquid and starch area. Stress can reduce kernel weight and yield; 35-42 days after silk, 20-23 days to maturity, 55% kernel moisture.
• R5.5—Mid-dent stage, when milk line is halfway down kernel; 90% whole plant moisture, 45-53 days after silk, 10-12 days to maturity, 45% kernel moisture.
• R5.7—Dent, when milk line is three-quarters of the way down kernel; 70% whole plant moisture, 50-59 days after silk, 5-6 days to black layer, 40% kernel moisture.
• R6—Physiological maturity, when milk line reaches kernel tip; kernels reach maximum weight, black layer forms at tip of kernel, field dry down begins. 52-55 days after silk, < 35% kernel moisture.

Talk to your Federated Agronomist for assistance determining your corn’s development stage as you make harvest plans.