How Much Defoliation Can Corn Stand?

Storms become talk of Corn Belt.

Published on: Jun 21, 2010

One storm after another has ripped through the Corn Belt from Minnesota to Indiana and all points in between and around these locations. You usually hear about or see pictures of the worst damage from hail or wind to crops. It raises the question - just how much damage can corn withstand and still produce a good crop?

Pat experience with hail in some fields indicates it depends upon how badly stalks are injured, and how many actual plants recover and can produce an ear. It also depends upon weather conditions that follow, whether the crop can be harvested before stalk rot sets in during the early fall, and perhaps most importantly, the final stand count after some plants don't survive. In the past, some fields that were pegged at 60 bushels per acre a week after the loss have topped 100 bushels per acre. Of course, there are no guarantees.

The Purdue University Corn & Soybean Field Guide published by Corey Gerber of the Purdue Diagnostic Training Center, carries a chart that predicts percent of yield loss based upon percent of leaf loss. The amount of yield you can expect to still receive varies greatly depending upon the stage of growth of the corn when the damage occurred.

For example, if corn is at the 7-leaf stage, according to the chart, there is no loss until you reach 40% leaf damage, and then it's 1%. Even if 100% of the leaves are destroyed, the expected yield loss from maximum potential is only 9%. That means a crop that should have yielded 200 bushels per acre could still yields approximately 180 bushels per acre even if all foliage was destroyed at the 7-leaf stage.

At the 10 leaf stage, likely where some of the corn hit recently was at when the damage occurred, the percent loss begins at 25% leaf area loss. But it tops out at 16% even if all leaves are destroyed.

As corn gets farther along in the process, the numbers rise dramatically for expected loss, especially if the damage is severe. At the 19 to 21 leaf stage, just before tasseling, if the field was hit, you could expect 3% loss even at 10% leaf loss. That jumps to 31% at 50% loss, and tops out at 96% loss is all leaves are destroyed at that stage.

Once the ear forms, the numbers actually decrease again. If corn is pummeled in the milk stage of ear development, expect only a 1% yield loss for 10% leaf loss. At 50% it's back down to 18%, and at 100% leaf loss, it would be 59%. That means that if a storm destroyed every leaf on a plant when ears were in the milk stage, the field should still make about 40% of originally expected yield.