Tennessee has a long enough growing season that any Early, Medium or Full relative maturity hybrid planted well into May will have enough heat units to make a corn crop. As a group, full season hybrids tend to have more ‘southern genetics’ which includes improved tolerance to heat compared to short season hybrids and they are considered first for late planting. However, a big negative for some producers may be the delay in harvest that comes with full hybrids compared to earlier maturity hybrids.
Bob Williams did a great job summarizing yields of county standardized plots from 2007-2010 comparing April vs May planting dates. I pulled information from his summary to create the table below. Note** most county plots are planted in April so in this table within a RM we are comparing only 1 to 5 May locations to 7 to 17 April locations:
| Year | EarlyRR | EarlyConv | MedRR | MedConv | FullRR | FullConv |
| (110-113 day RM) | (114-116 day RM) | (117+ day RM) | ||||
| % Yield DECREASE of May Planted Locations vs average of April Planted Locations | ||||||
| 2007 | ND | ND | ND | 0% | ND | 0% |
| 2008 | 0-24% | 5% | 3-10% | 9% | 0-8% | 0% |
| 2009 | 0% | 0% | 0-1% | 8% | 0% | 7% |
| 2010 | 27% | 0-3% | 11-23% | 0-8% | 16% | 3-15% |
| ND = no plots were planted after April for that year | ||||||
As a group, the Early RR hybrids planted in May appear to take higher hits on yield in poor corn years compared to the medium and full groups. So, if you are wary about this and your primary goal is to protect yield, look at more medium and full hybrids in your late planting situation.
On the other hand, producers who must harvest as early as possible in September to manage other crops more timely—will probably need to plant more acres in early and medium hybrids which is fine as long as they contain the best agronomic trait package you can get your hands on for late planting (heat/drought tolerance, standability, lower ear placement, good dry down, Bt, disease package).
One positive thing to come out of last year’s yield trials was the ability to identify those hybrids that performed well in a challenging year in several locations across the state. This information should be helpful when deciding what to keep and what to cull as the last corn planting decisions are made this month.
