B. Pollination and Grain Fill Conditions

Wet, warm summer favored high yields

Corn pollination typically occurs in July, and at pollination time, greater-than-average temperatures or lack of rain typically reduce the number of kernels. The weather conditions during the grain-filling period in July and August are critical to determining final grain composition. During this time, moderate rainfall and cooler-than-average temperatures, especially overnight temperatures, promote starch and oil accumulation and increased yields. Moderate rainfall and warm temperatures in the second half of grain-fill (August to September) also aid continued nitrogen uptake and photosynthesis. Nitrogen also remobilizes from the leaves to the grain during late grain-filling, leading to increases in grain protein and hard endosperm.

In 2016, areas in all of the ECAs changed from a very wet emergence period to a dry vegetative period, followed by abundant rains during the grain-filling period.In June, the warm weather and dry conditions favored rapid plant growth and nitrogen fertilizer uptake, producing a crop with a combined Good or Excellent condition rating that remained between 70-75% all season, conditions similar to the 2014 crop.The summer’s above-average temperatures in the Gulf and Southern Rail ECAs were mostly associated with warmer nights, potentially causing starch-accumulation stress during grain-fill.

It is thought that dry weather before pollination, followed by wet weather the first three weeks after pollination, favors Diplodia fungal infection of corn ears, which causes lightweight kernels, cob rot damage, and potentially more broken corn and foreign material (BCFM). While 2016 had prime conditions for Diplodia throughout the United States, especially the Pacific Northwest and Gulf ECAs, corn varieties differ in their susceptibility, and Diplodia is not known to produce any toxin harmful to livestock.

In the Pacific Northwest ECA,June was very warm (top-10 warmest over 100 years), while July, with average temperatures, was followed by August experiencing cooler temperatures more in the western area. Overall, June was dry, with timely rains for pollination, and then patchy areas of both drought and localized heavy rainfall the remainder of the summer, potentially leading to greater-than-average variability in grain quality.

While the Gulf ECAexperienced heavy rains, resulting in the fifth wettest summer on record, its rainfall was short of 2015’s rainfall. Warm nights, due to high dew points, were common during grain-fill in the Gulf ECA, potentially limiting maximum starch concentration.

Overall, the Southern Rail ECA was abnormally dry in June (10th driest of the 1885-2016 period) and warm (10th warmest since 1896). The western area of the Southern Rail ECA experienced close-to-average temperatures, and the southern section had greater-than-average precipitation. During grain-fill, there were warm nighttime temperatures with abundant rains throughout the Southern Rail ECA. These weather conditions encouraged greater-than-average oil concentration.