Crops - Crop Scene Investigation 10: What's really stressing John's corn?
Friday, February 29, 2008
It looked like drought stress, but other fields close by were not showing the same problems. And why was the stress more prevalent on the east side?
by SHAWN BRENNEMAN
It never hurts to get a second opinion. Sometimes it just confirms your initial diagnosis, but other times it will open your eyes to different possibilities.
In early August, I dropped in to see John, a dairy farmer in Oxford County. John and I walked several fields and discussed various issues, including the potassium deficiency dry weather had caused in his soybeans and how aphids might hurt yields. "Are you concerned about anything else?" I asked as we were wrapping things up. John thought for a moment and then pointed in the direction of a corn field that had him scratching his head.
On the way to the field, John reported that he'd had others look at the corn and the same diagnosis came back each time - drought stress. "It just doesn't make sense to me," he said. "I have other fields close by with lighter soil type and they're not showing the same stress as this field."
As we got closer to the crop in question, John gave me some history on the field. Last year's crop was conventional soybeans. He planted corn in the first week of May and applied a pre-emerge broadleaf and grass herbicide. He'd also side-dressed 28 per cent nitrogen based on a nitrate test, after applying liquid manure the previous fall.
The corn did appear drought-stressed at a first glance. I could see some leaf rolling and crop unevenness, both symptoms of lack of moisture.
I dug up several plants and found average root development.
One puzzling thing I noticed about the 50-acre field was that the stress was more prevalent on the east 25 acres.
I started questioning John to help make sense of the east-west difference.
"You said the crop last year was conventional soybeans. How was your weed control?" I asked.
"Not good," said John. "The annual grasses got away on us and hurt yields a little. We sprayed the soybeans late and it knocked back most of the weeds, but there was still quite a bit of grass and corn overall."
His comment about volunteer corn got me thinking. "What did you plant the year before the soybeans?" I asked. "Well, the west half was alfalfa and the east half was corn," he responded.
"John, I think I know what's going on here," I said. "Let's have another look underground to confirm my theory."
A closer examination showed signs of tunnelling and scar marks on the roots of the affected plants. I had my answer - and it wasn't drought stress.
Can you identify the problem with John's corn? Send your solution to Better Farming at:
rirwin@betterfarming.com or by fax to: 613-978-5993.
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
Shawn Brenneman, CCA, is a Field Agronomist for NK® Brand, Syngenta Seeds, based near Tillsonburg.