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Pro Farmer Midwest Crop Tour: The Race Against Frost

00:00AM Sep 05, 2008
Late-planted corn and soybean crops guarantee one thing: We'll worry about yield potential and beating the first frost until combines roll. But late plantings do not guarantee below-trend corn and soybean yields.

There's no doubt late plantings put crops at a disadvantage and leave them vulnerable to late-season stresses. But given the right conditions, corn and soybean yields can make trendline yields.

Corn crop conditions "good enough”
Throughout the 2008 growing season, crop watchers wondered how corn crop conditions could trend higher through the heart of the growing season despite late development. Many started to believe the development pace of the crop is irrelevant
in the condition rating. That's true. USDA's condition ratings are designed to quantify the overall condition of the crop regardless of the development pace. It's a measure of crop stress caused by weather or disease. If the crop is growing in relatively stress- and disease-free conditions, it should be rated at least "good.”

The last time the corn crop saw conditions increase through July was in 2004. That year, however, the corn crop was planted basically on time and crop conditions reflected the generally good conditions until early August. That's when disease caught up with crop development and conditions started a monthlong decline to a low posted the first week of September.

The pattern in condition ratings is where similari-ties between 2004 and 2008 end. In 2004, the season-long Pro Farmer CCI averaged 385 on the 0-to-500 scale. That, along with timely plantings, was good enough to push the national average corn yield to a record 160.4 bu./acre.

The 2008 corn crop did not see timely plantings. (If it was planted at the right time, the replanting was probably late!) And so far in 2008, the Pro Farmer CCI has averaged 364—about 20 points below the 2004 average. Ignoring late development, the higher-population 2008 corn crop is in good enough condition to hit USDA's Aug. 1 yield estimate of 155 bu./acre.

It just takes time
Late-planted crops simply need more time to reach full-yield potential. That seems obvious, but it's something many forget under the pressure of a long-drawn-out planting season. And it raises the question, "What is full-yield potential in a late-planted crop?”

Unless the 2008 corn crop somehow grows an average ear that weighs more than the historical average, USDA told us what full-yield potential is for the 2008 corn crop. In its Aug. 1 survey, USDA found a record stalk count in the 10 states. (That factor can't get any higher.) It then applied the historical average ear weight. Assuming below-average ear weights on the late-planted 2008 crop, the Aug. 1 USDA national average yield estimate of 155 bu./acre should represent full-yield potential.

Don't rule that out. Normal to above-normal temperatures after silking speed development and shorten the time for kernels to accumulate dry matter. Normal to below-normal temperatures after silking give corn kernels more time to accumulate dry matter. Extending the kernel-fill period for the 2008 crop, however, is dangerous. Pollination was, on average, about two weeks late across the Corn Belt, which means an extended kernel-fill period would project black layer beyond the normal first frost date in many areas.

The lesson learned from past Midwest Crop Tours tells us the prescription for the 2008 corn crop to reach its full-yield potential is: (1) average to slightly below-average temperatures after silking to get ear weights up to the historical average; (2) a two-week extension on the end of the 2008 growing season, pushing the first killing frost into mid-October. It's a long shot, but condition reports tell us the 2008 corn crop is pretty good at beating the odds.

Top Producer, September 2008