By Alison Robertson and Mark Licht
While the cool, wet conditions across most of Iowa have helped alleviate drought, they have interfered with cover crop (CC) termination ahead of planting. We normally recommend terminating CCs with a herbicide application at least 10 days before planting corn – because corn is a “princess” and there is more risk and potential issues when planted green (i.e. cover crop terminated at or after corn planting).
Planting green is associated with reduced corn yield.
We recently completely a multi-state project comparing “planting green” (winter cereal rye (WCR) CC terminated with glyphosate 0-3 days after planting corn) with “planting brown” (WCR CC terminated with glyphosate at least two weeks before planting corn) with the Precision Sustainable Ag team. In 2021, 2022 and 2023, the relative yield of corn planted green was lower than the yield of corn planted brown at 10 of 13, 11 of 14, and 10 of 12 locations respectively. To date, the mechanisms responsible for yield reduction in corn following WCR are unclear. Nitrogen immobilization, allelopathy, seedling disease, and planting errors have been hypothesized. In this blog we will focus on seedling disease.
Relative yield of corn planted into winter cereal rye (WCR) terminated with glyphosate at >14 days before planting (planting brown), 3-7 days before planting (planting yellow-brown) and 0-3 days after planting corn (planting green). Relative yield (%) = 100 – [(yield of corn planted after WCR/ yield of corn planted after fallow) X 100]
Corn seedling disease
Seedling disease of corn following a WCR CC is most often caused by Pythium spp. WCR is a host of Pythium spp. and when WCR is terminated, Pythium spp. are released from the dying roots.
Source : iastate.edu