Switch from full season to shorter season corn varieties?


Tony Nye - OSU Extension



We all know the story — much of Ohio has been dealing with cool temperatures, and saturated soil conditions have delayed corn planting. According to the USDA/NASS, during the past week, Ohio corn acreage planted increased slowly (from 30 percent for the week ending May 8 to 34 percent for the week ending May 15).

Locally we may have increased a little for a few brave souls that planted in less than ideal soil conditions. Sometimes “ya gotta do what ya gotta do.” The weather forecast maybe shows some promise now for more nice days that are drier, sunnier and warmer.

Given this outlook, is there a need to switch from full season to shorter season hybrids? According to our Ohio State University corn specialist, Peter Thomison, the answer is probably not — in most situations full season hybrids will perform satisfactorily (i.e. will achieve physiological maturity or “black layer” before a killing frost) even when planted as late as May 20-25, if not later in some regions of the state.

Results of studies evaluating hybrid response to delayed planting dates indicate that hybrids of varying maturity can “adjust” their growth and development in response to a shortened growing season. A hybrid planted in late May will mature at a faster thermal rate (i.e. require fewer heat units) than the same hybrid planted in late April or early May).

Thomison notes in Ohio and Indiana, they have observed decreases in required heat units from planting to kernel black layer which average about 6.8 growing degree days (GDDs) per day of delayed planting. Therefore a hybrid rated at 2800 GDDs with normal planting dates (i.e. late April or early May) may require slightly less than 2600 GDDs when planted in late May or early June, i.e. a 30 day delay in planting may result in a hybrid maturing in 204 fewer GDDs (30 days multiplied by 6.8 GDDs per day).

There are other factors concerning hybrid maturity, however, that need to be considered. Thomison states that although a full season hybrid may still have a yield advantage over shorter season hybrids planted in late May, it could have significantly higher grain moisture at maturity than earlier maturing hybrids if it dries down slowly. Moreover, there are many short-to mid-season hybrids with excellent yield potential.

Therefore, if you think you may end up planting in late May/early June, consider the dry down characteristics of your various hybrids. In recent years they have seen a wide range of drying conditions. In some years, mid- to full-season hybrids had grain moisture levels at harvest similar to those of short season hybrids because of rapid dry down rates. However in other years, cool, wet conditions after maturity slowed dry down and major differences in grain moisture at harvest were evident between early and full season hybrids.

Late planting dates (roughly after May 25) increase the possibility of damage from European corn borer (ECB) and warrant selection of ECB Bt hybrids (if suitable maturities are available). In past OSU studies, ECB Bt hybrids planted after the first week of June consistently outyielded non-Bt counterparts even at low to moderate levels of ECB.

Since most Ohio corn growers typically plant hybrids that include Bt resistance for ECB, this is usually a non-issue unless there is a need to switch to earlier maturing hybrids.

What does history tell us on late planted corn and its relationship to yield? Since 1980 there has been nine years we have planted significant acres (40 percent or more each year was not planted by May 20) due to wet spring weather. By May 30 of those nine years, seven of those years we still had between 35 to 60 percent of the corn crop to plant. The other two years had 77 percent and 95 percent of the corn planted by the end of May.

According to Thomison, in five of the nine late planted years average state yields were markedly lower than the state average yield of the previous five years. Two of these we saw yields 25 bushels or more below the five year average. 2002 was the worse at 88 bushel per acre state average yield compared to the sate-wide five year average of 138 bushel per acre.

However, Thomison notes that in four of the nine years, yields were similar or higher than the statewide average yield of the previous five years, and in one of these years, 2009, a record high corn yield, 174 per acre, was achieved compared to the five year average of 149 bushels per acre.

Bottom line, this is not the first time we have had this issue. Hopefully by the time Saturday is around we will have wonderful planting conditions and we can get caught back up significantly with both corn and soybean planting.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for 28 years, currently serving Clinton County and the Miami Valley EERA.

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Tony Nye

OSU Extension

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