Crop Scene Investigation - 55: What caused 'death on the knolls' in Dave's cornfield?

Saturday, January 31, 2015

by BERNARD TOBIN

As Aric Bos drove his pickup past Dave's cornfield, he instantly spied the trouble the south Huron County grower had described during his morning phone call.

Exiting his truck, the Pioneer agronomist scanned the 100-acre field. It wasn't a pretty picture. The six-to-eight-leaf corn appeared to have good stand establishment and the population looked sufficient, but in many areas of the field – about 10 acres in total – the corn was pale, yellow and stunted, and had very acute purple leaf margins.

As he walked the field, he noted the problem appeared to be confined to the sandy knolls scattered throughout the field. "It certainly was 'death on the knolls' as Dave had described," recalls Bos. "The plants were shorter, sick and already had some browning older leaves. At the bottom of the plants, some leaves had already died off. It was pretty bad for six-inch corn."

Nitrogen deficiency was the first potential cause that popped into the agronomist's head as he surveyed the carnage. But, after talking with Dave, he quickly ruled that out. "The grower was following a strong fertility program and, despite a wet spring, there's no reason the crop would be short nitrogen this early, even on the sandy knolls."

Talk of the weather continued as the two men walked the field. Dave's farm had been drenched with 11 inches of rain the previous October and deep snow cover from the winter of 2013/14 produced even more excessive moisture during snow melt.

As he examined the stunted plants, Bos thought the symptoms could be the product of micronutrient deficiencies, things like magnesium and sulphur. "I shared that thought with Dave, but he said micronutrients couldn't be a problem. Further discussion of the fertility program indicated that the micros should be fine. He had even limed the field in the fall to help maintain pH levels."

The field was planted to soybeans the previous year, but Dave said there was no similar performance pattern compared to what they were now observing in the following corn crop. Bos even thought about compaction and the possibility of sand blasting with the high level of sand on the knolls, but he quickly dismissed both ideas as being the primary cause.

Bos also ruled out herbicide injury after examining the roots of the poorly-performing plants. "In those cases, you typically have root damage, but the roots were fine – the plants were just smaller with shorter internodes."

With no obvious answer to the puzzle, Bos collected some plants for tissue analysis as well as soil samples from the poor-performing areas in the field. It really was a eureka moment when he saw the results. The plants tested low for magnesium and sulphur at 0.28 per cent and 0.17 per cent, respectively. When he looked at the soil test, the pH was in the 4.5 range.

Do you know what caused the death on the knolls? Send your solution to Better Farming at: rirwin@betterfarming.com or by fax to: 613-678-5993. Please provide your contact information.

Correct answers will be pooled and one winner will be drawn for a chance to win a Wireless Weather Station. The correct answer, along with the reasoning followed to reach it, will appear in the next issue of Better Farming. BF