Grain fill critical for 2019 corn

July 5, 2019

The reality is that most corn in the eastern Corn Belt was planted late. In many cases the soil was almost too moist, but seed had to be planted.

The Corn Watch ’19 field, sponsored by Seed Genetics Direct, in central Indiana normally is planted by the last week of April; this year it was planted May 28. Reports on this field’s progress will be provided all season (#CornWatch19); read the latest Corn Watch ’19 articles here.

When Dave Nanda, PhD, SGD director of genetics, first observed the field on June 12, corn plants were in the three-leaf stage. The month of June turned out rather cool and wetter than normal. That may have resulted in slower root development.

Pollination and grain fill

What effects could late planting have on the grain-fill stage for corn after pollination this year? How will yield be affected if it is hotter than usual in August?

First, what we know: Corn will need 50 to 60 days for grain fill after pollination to reach physiological maturity, depending on relative maturity of hybrids and prevalent temperatures. During grain fill, corn plants try to pack as much dry matter into kernels as possible. Corn likes cooler temperatures and sufficient water and nutrients during this critical period for optimum yields. Stresses during grain fill have a negative effect on yield.

Some things can go wrong during pollination, before grain fill. If pollination of some ovules isn’t successful due to stress, there may be an incomplete kernel set. Japanese beetles and corn rootworm beetles, which feed on pollen in silks, can also interfere with pollination and reduce kernel set. Heat and drought stress could delay silk emergence and cause pollination problems too. Late-emerging silks may not find any pollen left to fertilize ovules and form kernels. The first silks emerge from the butt of the ear and the last silks from the tip. Kernels near the tip are more likely to be left out of the pollination process if conditions aren’t ideal.

Grain-fill period ahead

If there’s severe heat, lack of moisture or disease stress during grain fill, plants may cannibalize stalks and leaves to fill the needs of their progeny: the kernels. Cooler temperatures and enough moisture will help prevent these conditions from developing.

Toward the end of grain fill, farmers can determine if black layer has occurred. That may prove especially important this year in some later-planted fields. Crops could be racing against the calendar to mature in time.

Dissect kernels with a pocketknife. When dissected kernel tips start showing a black layer, kernels are mature and no more nutrients can enter. Typically, kernel moisture is 32 percent to 33 percent at this stage. When black layer occurs, the grain-fill period is complete.