University research shows that full-season hybrids adjust to late planting with a reduction in their growing degree unit (GDU) requirement of up to 6 units/day of planting delay. For example, hybrids planted May 20 may require 150 fewer heat units to reach maturity than the same hybrids planted April 25. This adjustment reduces the risk of fall frost damage to these hybrids.

Pioneer studies across several years reinforce the university findings. Pioneer focused on hybrids planted across the central, north-central, north and far-north regions of the Corn Belt. Hybrids were planted from early April to mid-June and grouped into full, medium and early maturities at each location. Several hybrids were included in each maturity group so that true maturity responses could be measured, rather than just specific hybrid responses. The studies looked at differences in corn grain yield response to planting date, as well as moisture, test weight and gross income response. The data provide growers more relevant planting information for the different regions in which they farm.

For example, in the central Corn Belt, results indicate that early to mid-April planting is best for the greatest corn yield potential. Full-season hybrids – hybrids with a comparative relative maturity (CRM) of 111-115 – yield better and produce better grain at harvest than early-maturity hybrids. Growers should not consider switching full-season hybrids to earlier CRM hybrids until the last week of May.

Soil conditions permitting, April planting also is recommended in the north-central Corn Belt. Growers are encouraged to plant full-season hybrids (103-110 CRM) until the last week of May in this region.

Maturity planning is most critical in northernmost states because of the risk of cool weather or early frost. Pioneer recommends producers in northern Corn Belt areas (central Minnesota and north-central Wisconsin) stick with full-season hybrids (98-105 CRM) until approximately May 27.  This recommendation also carries into far-northern areas (northern Minnesota, North Dakota and Quebec, Canada) for hybrids that are full-season there (97-100 CRM).

Growers with questions about specific hybrid characteristics and environmental effects should talk to their seed sales professionals.


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