The effect of corn planting date, stand establishment and uniformity has been addressed by Emerson Nafziger, University of Illinois Extension corn specialist in the last two editions of the Pest Management & Crop Development Bulletin. The topics are especially timely given the delayed spring field work in northern Illinois.

Based on research at DeKalb and Monmouth from 2005-2008 in which corn was planted from early April to early June; yield losses reached 1 bushel per day by early May in northern Illinois. As shown in those studies, losses of 1, 1½, and 2 bushels per acre occurred for each day of delay during the first, middle, and last third of May, respectively. Yield loss approached 2½ bushels per day for each day of delay in the first third of June.

Nafziger noted that planting on May 1 is expected to yield only 7 or 8 bushels per acre less than planting on the optimum date (April 12) in northern Illinois. Delays in planting until past the end of April, though they cost some yield, do not automatically mean large yield losses.

Regarding stand establishment and uniformity, Nafziger indicated that uniform spacing of plants in the row is less meaningful as populations increase. Plant populations today have average plant spacing often about 6 inches or less.

Secondly, if we are reaching our target population, there is almost no chance that uniformity of interplant spacing has a measurable effect on yield. If there is an effect, it is likely too small to spend money to correct.

Nafziger summarizes the topic by saying that uniformity of seed placement is important, to the extent that it affects uniformity of emergence. Uneven plant size early translates to yield loss. Efforts to place seed at uniform depth and into uniform soil conditions will likely pay off. Planting at 1¾ inches deep is a good target.

The Pest Management & Crop Development Bulletin can be found online at http://www.ipm.uiuc.edu/bulletin/contents.php The information mentioned above is in Bulletin number 3 and 4.