Assessing late planted corn for harvest as forages

The U2U tool developed by several Midwest land grant universities can help assess and predict corn maturity.

two ears of corn, one small and underdeveloped
Large differences in corn maturity planted less than one month apart in spring 2019.

At some point in the near future, growers should begin to critically assess if their later planted corn fields will develop enough before a killing frost occurs to produce viable grain. For corn grain to be marketable, the crop needs to have a reasonable chance to reach black layer, the thin abscission layer that keeps the kernels from losing dry matter content during the dry down period. The good news is that temperatures are expected to heat up during the next couple of weeks, which should help provide much needed growing degree units needed for the later planted corn to continue to develop. The unfortunate news is that drought stressed crops are falling behind in growth, and will need irrigation or rainfall to help the plants to be able to utilize the growing degree days expected during the next two weeks.

Research conducted by Dr. Bob Nielsen at Purdue and Dr. Peter Thomison at Ohio State showed that corn can undergo compression during the reproductive stages of growth to help reach black layer. That might mean good news for some of the later planted corn. However, much of the states later planted corn has not yet reached full tassel. On average, full silking occurs 4-6 or so days following tassel emergence. It takes somewhere between 50-55 days after silking for corn to reach black layer in a normal year. As we near the end of August, we are going to be entering relatively uncharted waters in terms of corn growth and development after silking of the later planted corn. I think it is fair to say that with each passing day, corn that has not yet tasseled will need progressively more optimal growing conditions through the fall to reach full maturity. Corn not likely to reach physiological maturity would make a better candidate for harvest as silage or green chop for a livestock producer. If you do not have a way to feed immature corn, you might want to visit with local livestock producers to come up with a “Plan B” for your latest planted fields if the weather does not go according to plan.

Several of the Midwest Land Grant Universities co-developed a tool that can help predict when your corn might reach black layer. It can be found at the Useful to Usable Corn GGD Website at: https://mrcc.illinois.edu/U2U/gdd/

You will have to enter your location, the maturity group of your corn, and planting date. It is important to keep in mind that this model does not use compression to shorten the number of days it takes for your hybrid to reach black layer. It will, however, give you sort of a worst-case scenario about when your hybrids should reach maturity and the expected dates of a killing frost. Pay attention to the dark Gray Shaded Region, which shows the highest and lowest expected GDD accumulation for the rest of the season. The red line shows anticipated silking date, the dashed line shows the anticipated GDD’s for 2019. The dashed vertical line shows the first likely black layer date, the solid black vertical line shows the expected black layer date. The blue bars at the right show the probability of the first 28-degree night. Remember, this is just a projection, not what is going to happen. Warmer than normal temperatures will help speed the development of the crop under good growing conditions.


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