The timing of the first 28 degree F frost this fall will affect corn yield potential in Iowa, thanks to later-than-normal crop development. A later-than-normal frost would encourage a longer seed-fill period and higher yields, while an early frost would certainly not be the ideal situation.
Cool August temperatures across Iowa slowed growing degree day, or GDD, accumulations. In addition, Iowa's late corn planting dates this year obviously impacted the crop as well. These two factors affect corn yield potential.
Iowa State University Extension corn agronomist Roger Elmore is keeping track of GDD accumulations. Growing degree day accumulations in Iowa lag behind normal. Cool temperatures after silking not only slow GDD accumulation, thus slowing crop development, but also can increase yield potential given specific conditions, he says. The record yields of 2009 resulted from slow GDD accumulation after silking -- coupled with a late frost. On the other hand, warm temperatures after silking in 2010 reduced corn yield potential (See an ICM News article reporting this).
Late-season corn development and first frost probabilities in Iowa
Earlier this season Elmore addressed the potential impact of late corn planting on yields; see Crop Model Output and Field Research Data. The August 12 USDA yield forecast in part reflects this; Iowa's USDA August forecast yield of 163 bushels per acre is almost 9% below 30-year trendline yields (10% below the 30-year trend is "officially" a drought).
Dry matter accumulation and grain moisture during reproductive stages
Let's address another question: Will Iowa's 2013 corn crop mature before frost? "My response to this question depends on when the first 28 degree F or colder frost occurs and the crop's current development stage," says Elmore.