Crop Scene Investigation - 8: What was the trouble with Troy's stunted corn?

Wednesday, January 16, 2008

by DEB CAMPBELL

Time is of the essence. This is especially true when you have a crop which doesn't look healthy. Promptly figuring out why the crop isn't thriving and taking action to correct it will help you maximize yield.

Time was ticking on the growing season when Troy, a Peel County corn grower, called me in early June. His month-old corn crop was in need of help. "My corn is yellow and stunted in two separate fields. It must be a hybrid issue," he said.

I'm not one to jump to conclusions without a thorough check. We talked about the fields' histories. Both were sandy loam soil, but with different crops and herbicides the year before - one was Roundup Ready soybeans and the other was green beans in which weeds were controlled mechanically. This information ruled out any carryover issues.

I arrived at the field to find that the corn was yellow and stunted, just like Troy described. "I noticed the crop wasn't right two weeks ago," he said. "I assumed it was temporary." By the time I was called to help, some plants were actually dead. The growing point tissue was dead and the newest leaf had turned brown.

But I also noted that some random plants were completely unaffected. There was variable crop staging across the field as well. Troy's corn ranged in size from five leaf to eight leaf.

The injury symptoms could be the result of many things. I thought about the potential of wireworm or chafer damage, but I couldn't find any signs of feeding. Root rot came to mind as well, but the seed had been treated with a fungicide and there were no lesions on the roots.

I also noted a pattern throughout the field which appeared to be the result of an over-the-top spray. The damage was self-contained in the two fields, which told me drift wasn't a factor here.

You could see where the sprayer had overlapped at the headlands and around trees. The intensity of the symptoms worsened dramatically in these areas. "Tell me about your herbicide program," I said.

Troy paused to recall the details.

It had been a busy time and he had treated a lot of acres. "We applied the herbicide early post-emergence," he recounted. The spray program he used features superior crop safety, so I was really puzzled. And why were 20 per cent of the plants completely unaffected?

We'd need some definitive answers before we could set these fields to rights. It was time to take advantage of new diagnostic tools, so we sampled tissue and sent it away for analysis at the University of Guelph's crop diagnostic lab.

In the meantime, we found an unsprayed patch of plants in the back corner of the field. This check showed no injury symptoms and there was significant weed pressure.

When the lab results came back, I had my answer.

Can you identify the problem with Troy's corn?

Send your solution to Better Farming at:
rirwin@betterfarming.com
or by fax to: 613-978-5993.
Please include your address and phone number.

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

Deb Campbell, CCA, is a Field Agronomist for NK® Brand, Syngenta Seeds. She is based near Dundalk.