Growth and Development of Late-Planted Corn

• Field corn growth and development largely depends on temperature. The generally accepted method of tracking development is to calculate accumulated growing degree days (GDDs). Warm temperatures lead to rapid GDD accumulation.

• Black layer occurs at maturity and is the formation of a layer of dead cells where the kernel attaches to the cob (Figure 1). Once black layer forms, no further photosynthates can be delivered to the kernel – only drying down (loss of moisture) can occur.

• If a killing frost occurs before black layer, while the milk line is still visible, there can be a negative impact on yield potential (Figure 2).

• The 2019 planting season was extremely challenging throughout much of the Corn Belt. There were approximately 2 to 3 days with conditions conducive to planting in the months of April and May. Much of the crop was planted after June 3^rd. The major delays in planting led to concerns of full-season hybrids having insufficient time to develop before the first killing frost. 

• Previous work at Purdue University indicated that late-planted corn can develop with fewer GDDs, helping to alleviate those concerns.¹ 

• Guidance was given to many farmers that switching to an earlier-season hybrid was not necessary in many cases based on the understanding that fuller-season hybrids could reach black layer before the first average frost date. However, as the growing season progressed, this accelerated development did not seem to take place.

• Two SmartStax® RIB Complete® corn blend products with relative maturities (RM) of 108-day and 114-day were planted on two different dates:
  • 4/25/19 (early)
    
  • 6/3/19 (late)  
    

• Accumulated GDDs as well as elapsed calendar days were recorded for two key developmental stages: silking and black layer.

   

• The 108RM corn product developed at a similar pace in both plantings. Key developmental stages were reached slightly sooner in the later planting, but not substantially different. 

• The late planted 114RM corn product developed much faster during the vegetative stage – developing silks 170 GDDs sooner than that of the early planting. This is in line with expectations from the earlier research at Purdue.1

• However, during the reproductive stages, development in the 114RM product seemed to regress. Black layer was reached only 47 GDDs sooner in the late planting. This agrees with observations from throughout Illinois. In some instances, black layer reportedly occurred even later than normal. 

• It is not entirely clear what caused this to occur, but there is some indication that reduced sucrose production as the leaves mature and die may be involved in triggering black layer.² If this is the case, warmer than normal temperatures in September led to increased stay-green and extended sucrose production. Consequently, there was delayed black-layer formation. 

• Stay-green also may have been prolonged by plentiful rainfall, which came after a 6-week drought during July and early August, possibly stimulating increased photosynthesis and additional sucrose production.

• In many circumstances, late-planted corn can develop at an accelerated pace – reaching key growth stages with fewer accumulated GDDs. This possibility would increase the likelihood of black-layer development before a killing frost.

• This accelerated development may not happen every season, particularly in conditions that prolong stay-green and photosynthetic activity in the fall.

• Corn growth and development can be highly variable – consult your local Field Sales Representative or Technical Agronomist for product recommendations to fit your specific circumstances.

¹Nielsen, R.L. 2019. Hybrid maturity decisions for delayed planting. Corny News Network. Purdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/hybridmaturitydelayedplant.html

²Afuakwa, J.J., Crookston, R.K., and Jones, R.J. 1983. Effect of temperature and sucrose availability on kernel black layer development in maize. Vol. 24(2). Pgs. 285-288.

Sources verified 11/2/2019, 3013_R2