Crop Scene Investigation - 9: What had been feasting on Matt's corn roots?

Thursday, January 31, 2008

by MIKE FOLKARD

Crime suspects don't hang around the scene waiting to get caught. The same is true of some yield-robbing pests. They often flee without detection, but that doesn't mean the trail of evidence has gone cold.

Things were heating up for an Elgin County grower early last summer after he noticed some damage in his cornfield. "I don't like what I'm seeing in one of my fields," said Matt. It was mid-June and he had just finished spraying his six-leaf corn. As he covered the ground with the sprayer, he had a good look at his crop. "There are some spots without any corn and, in some cases, plants have emerged, but they look wilted."

This problem could be due to any number of things and I'd need to get into the field to investigate.

Matt wanted to finish up the rest of his spraying, so he agreed to meet me a few days later.

By this time, the corn had progressed to the seven to eight leaf stage. I had some questions for Matt before I dug around in the sandy loam soil. We ruled out fertility problems and the possibility of fertilizer burn. His planting depth also checked out. "What about the conditions after emergence?" I said, wondering about the possibility of crusting due to a heavy rainfall, which would make it difficult for the seedlings to emerge.

"We had some nice rains before and after - nothing that would have caused crusting or compaction," said Matt. That also ruled out poor seed-to-soil contact. There should have been enough moisture to germinate the seed.

As I walked the field, I noticed the gaps where corn hadn't emerged and where some seedlings had died back.

I decided that the damage was caused by insects below the surface. If so, we'd likely find the culprits underground.

I dug up the dying plants and, as suspected, found evidence of feeding on the roots. I wondered about wireworm and seed corn maggot, but couldn't find these insects - or any others, for that matter.

I started digging deeper to see if I could find any pests below the root zone, but came up empty-handed. I then dug between the rows and, again, no luck. Finally, I went to another damaged patch and looked closely at the soil before I put my shovel in the ground. That's when I noticed several little holes - about the circumference of a pen - and dry pieces of skin on top of the soil. I had my answer.

Can you identify the problem with Matt's corn? Send your solution to Better Farming at:
rirwin@betterfarming.com or by fax to: 613-678-5993.

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

Mike Folkard, CCA, is a Field Agronomist for NK® Brand, Syngenta Seeds. He is based near Belmont.