If you want a classic picture of the result of corn borer damage, find a picture of an ear of corn laying on the ground before harvest. Especially second-generation corn borers, very hard to control with sprays, are noted for boring into ear shanks and causing dropped ears. It's less of a problem today since so many farmers plant stacked hybrids that contain the corn borer resistance trait, but it's still possible to see it, especially in conventional fields where transgenic corn isn't planted.
However, just because you plant stacked hybrids, or at least hybrids with Bt corn borer protection, doesn't mean you won't see dropped ears. That's one lesson that came out of the Corn Illustrated plots sponsored by Farm Progress, and conducted near Edinburgh, Ind., this year.
Stress can also result in ear drop, notes Dave Nanda, president of Bird Hybrids, Tiffin, Ohio, and crops consultant for the Corn Illustrated project. In particular, the stress of planting too thick can produce increased ear drop. It was a tough, stressful year in central Indiana, with below-normal rainfall and high heat many days, particularly late in the season. But even in irrigated corn, Nanda noticed increased ear drop in high yield plots where corn was dropped at 41,000 seeds per acre. It's something he has noticed before.
And it can be costly. When estimating harvest losses, after counting whole kernels, ag engineers note that in 30-inch rows, you should count the number of average-size, whole ears left behind along 175 feet of a single row. Each ear not harvested amounts to roughly one bushel per acre of loss. So even though plot yields topped well over 200 bushels per acre in some cases, perhaps they could have been higher yet if all the corn that grew in the field was turned into shelled corn in the grain tank, Nanda observes.
He found spots where as many as five to six ears or more were dropped in 175 feet. Exact data will be available once calculations are finished on this year's plot harvest information. But even at five dropped ears, that's 5 bushels per acre of loss before the combine ever reached the corn. With corn at $2.50 per bushel, that's $17.50 per acre off the top, not counting the extra cost of seed to go to such high population levels. Nanda did not notice appreciable ear drop at the base population in the plot- 32,000 plants per acre. That's the planting rate that the farmers, Jim, John and Ryan Facemire, usually follow on those irrigated soils.
Nanda questions whether 32,000 plants per acre is necessary, especially on soils prone to drought. It certainly wasn't a help over more moderate populations on non-irrigated, droughty soils in '07. Plots in another droughty field in the Corn Illustrated project proved that point.
The crops consultant and former seed breeder hopes to help farmers who want to work with him evaluate their plans for growing corn in '08, including selecting seeding rates. "Someday we'll grow corn at 70,000 plans per acre," he says. That's the population he uses in his selection nurseries today.
"But for the time being, our production systems aren't designed to handle super-high populations. Corn is grown in 30-inch rows and is not spaced equally. It's not a contradiction to say some people plant too thick today, and yet say someday we'll plant much thicker all at the same time. Those future rates will be part of a system. In today's system, I'm not convinced you need to go to populations as high as what some people are planting to set yourself up for excellent yields."