Weather Impacts on Corn

Everybody who grows corn knows that the recent hot, dry weather during pollination isn't ideal. The question then becomes how to assess what the impact has been.

The most accurate way is to simply go out and do yield checks by counting ears and kernels. Rather than spell this out here, I'll refer people to Bob Nielsen's article from last October, Estimating Corn Grain Yield Prior to Harvest. In talking to people who've done this already, the general response I'm getting is, "It's not as bad as I was afraid it might be." I know that's not terribly specific but it appears that the corn has been weathering this surprisingly well.

From "drive-by windshielding" there has been remarkably little visible signs of stress in corn, in particular leaf rolling. This has recently started to change a bit in areas of the county which have not received much rain. If you're wondering how leaf rolling equates to yield loss, I'll refer you to an article from July 15 by Roger Elmore and Elwynn Taylor from Iowa State, Corn and “a Big Long Heat Wave on the Way”. In particular, these passages in the final section are interesting:

"By rule-of-thumb, the yield is diminished by 1 percent for every 12 hours of leaf rolling - except during the week of silking when the yield is cut 1 percent per 4 hours of leaf rolling."

and

"The second impact is less obvious initially. When soil moisture is sufficient, as it is for the most part this July, the crop does not have a measurable yield response to one day of temperatures between 93F to 98 F. However, the fourth consecutive day with a maximum temperature of 93 F or above results in a 1 percent yield loss in addition to that computed from the leaf rolling. The fifth day there is an additional 2 percent loss; the sixth day an additional 4 percent loss. Data are not sufficient to make generalizations for a heat wave of more than six days, however firing of leaves then becomes likely and very large yield losses are incurred."

Unfortunately, just in the past few days there has been some lower-leaf firing in corn. As a caution, this goes back to my "drive-by windshielding" sampling method which tends to include quite a bit of end-rows which are generally more compacted and will show more of this.