Crop Scene Investigation - 47 Solved: What's stalking Stan's corn?

Thursday, December 5, 2013

When DeKalb agronomist Bob Thirlwall looked into the whorl of one of Stan's corn plants, he found armyworm.

The pests had left the neighbouring rye field and set out to look for a new source of green vegetation after Stan disked the crop. "Obviously, armyworm moths had flown into the rye in early spring, laid their eggs and the larvae had been feeding on the crop," explains Thirlwall. "As soon as you take away that green matter, they look elsewhere."

The hybrid planted next to the rye – DKC50-45, a Genuity SmartStax hybrid – contains the MON89 trait, which includes Cry 1A and Cry1F proteins that protect the plant against the pest. But just farther north, a second hybrid, DKC52-59 with YieldGard VT3 protection, proved appetizing to the marauding armyworms because it does not contain the protective proteins.

"It was incredible to me to find that 50 or 100 feet of corn was untouched, and right to the line where the hybrid switched, you have a disaster. They marched right through the first hybrid and started feeding on the second hybrid," says Thirlwall. "It really shows what a difference the technology can make."

With the mystery solved, the first course of action was to spray the affected hybrid with an insecticide to stop any further feeding. Stan's next task was to determine whether a replant was necessary. "The big challenge was evaluating the plants that had been chewed down. You have to determine how many of those are going to pop back up," explains Thirlwall.

"We left the field for a couple of days to see if the chewed plants would come back. Then we were able to determine what parts of the field needed replanting without losing the planting window," adds Thirlwall.

Congratulations to Wayne Sutherland, Beeton, for his correct answer. BF