Much of the US Midwest was planted to corn much later than normal because of weather problems. Instead of corn planted in relatively cool soils and cooler air temperatures of April and May, corn was planted in June. Temperate zone adapted corn apical meristem is stimulated to switch from producing leaf and stalk cells to flowering structures by accumulation of heat energy estimated by growing degree heat units. June and July temperatures being warmer than the usual April and May temperatures should lead to a quicker change to the apical meristem switch to flowering structures.
Plant height is determined by the number of stalk cells produced by the apical meristem plus the elongation of the cells mostly affected by water infusion before the cell walls solidify. It will be interesting to see if the rapid growing degree accumulation of the extreme late planted corn reduce the number of stalk cells than normal, resulting is shorter hybrids than expected. Will all hybrids show the same reaction? Will we see a difference in timing between pollen production and silking? We should learn something new about corn maturity and heat during the next few months.
The blog post below from Corn Journal 10/5/2017 speaks to the issue of heat units and flowering.
RELATIVE CORN MATURITY
Heat is a major energy factor influencing the development of corn plants and the ultimate grain yield. Cellular respiration rates increase as temperatures go up. Photosynthesis rates also respond to increased heat as well. It seems reasonable to assume that practically every physiological function in the corn plant is affected by heat energy.
This includes the transformation of the apical meristem from producing leaf buds to production of the tassel. This happens in corn plants at about the V6 stage. Many, many years ago, I dissected young corn plants of hybrids of nearly all maturities sold by a major seed company looking for this change in the apical meristem. The change visible under a microscope, was nearly perfectly correlated with our final classification of the relative maturities of the hybrids. This is consistent with the view that the first influence of temperature on corn maturity occurs early in the season. It is probable that temperatures further affect further development of the differentiated apical cells into mature tassels. We attempt to express the daily temperatures that could affect the timing of pollination with averaging high and low daily temperatures but accurately depicting the duration of a high or a low temperature is difficult. We know that it does affect, but like much of growing crops, we know of the principles but not all the specifics.
Grain fill period seems mostly fixed to about 55 days but there are studies that show low night temperatures can extend the period to formation of the abscission layer, thus increasing grain yield (Elmore, R. 2010. Reduced 2010 Corn Yield Forecasts Reflect Warm Temperatures between Silking and Dent. Integrated Crop Management. Iowa State University, 9 Oct. 2010). It is likely that each hybrid differs in its reaction to temperature during this period.
Given the difficulty of accurately measuring the specifics of temperature interactions of corn plant morphological development, cellular function such as photosynthesis, respiration rates and translocation rate of sugars It is best that we simply compare hybrids for their usual time to harvest moisture. It is all relative.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.