Features Agronomy Identity Preserved
Corn and cold September nights

Sept. 22, 2009

Greg Stewart, OMAFRA

A combination of late planting dates in many areas of the province along with crop heat units accumulating at a pace somewhat behind normal has caused an increased level of anxiety over cool September nights were the risk of frost looms large. The actual level of anxiety for most growers will be determined by the stage of maturity their grain corn crop has reached.

As temperatures drop to zero frost damage first occurs to the leaves of the corn plants. This damage will eliminate any further photosynthesis, reduce grain filling and often have a negative effect on stalk strength. However, as long as air temperatures do not fall below –2 Celsius stalk tissues will remain viable and stalk constituents will be mobilized to fill the ear as much as possible. If on the other hand temperatures fall below –2 Celsius both leaves and stalks may be damaged and no further photosynthesis, or remobilization can occur. This will terminate grain filling and kernel black layer will develop. Table 1 outlines the potential risks to yield and quality for grain corn experiencing different levels of frost damage.

Generally growers will recognize the early dent stage as being the cut-off point where corn can withstand frost damage to the leaves and still produce a reasonable grain yield. This stage is characterized by having kernels, at least in the lower half of the cob, showing small indentations in the crown of the kernel. It should also be noted that grain quality concerns are based mostly on low test weights. However, most of the experience and research from Ontario and other jurisdictions indicate that the feed value of low test weight corn (46-52 lbs/bushel) is quite similar to normal test weight corn.

The other question regarding cold nights revolves around the corn crops ability to continue grain filling after experiencing several cold nights but were no frost damage occurs. Dr. Thys Tollenaar, University of Guelph has conducted research where he measured 50 percent reductions in photosynthesis and rate of grain filling due to cold nights of minus 2 degrees Celsius. However when these plants were restored to higher temperature conditions they resumed plant activities at rates similar to those plants that had never experienced the low temperatures. Producers can take heart in the fact that if cornfields can escape any serious frost damage during cold nights that grain filling will carry on once normal temperatures return.

In some situations frost damage will preclude harvesting the crop as grain and will force the grower to consider harvesting it as silage. There are important issues surrounding the management of the silage crop as well. Following a frost, silage corn frozen before reaching the half milk line on the kernel may be too high in moisture to properly ensiled. In cases of frost, ideally corn harvest should be delayed until the whole plant reaches the desired moisture content for ensiling. Recommended corn silage moisture content for optimal fermentation are: 60 to 70 percent moisture for an upright top unloading silo, being closer to 60 for the taller silos’, 50 to 60 percent moisture for an upright bottom unloading silo and 67 to 72 percent for a horizontal or bunker silo. Excessive silage moisture at harvest can also lead to storage seepage and unloading difficulties in winter. Often after a frost event, and with rapid change in leaf colour, standing corn appears drier than it actually is. Check whole plant moisture content and be sure to get silage moisture correct for proper storage