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Managing overwintering corn

Leaving corn unharvested over winter poses a new set of problems. Photo courtesy of David Hooker.  

There are years when it can be extremely difficult for farmers to harvest some of their corn acres. Excessive rainfall during the harvest period may result in fields that are too wet to be combined. In other years, cooler-than-normal weather during the growing season can result in high grain corn moisture levels and prohibitively high drying costs. In this case, farmers may opt to harvest the corn in spring, leaving it to dry down naturally to reduce drying costs.

However, leaving the corn unharvested over winter comes with another set of challenges. There is an increased risk of lodging over winter, impacting crop harvestability and grain yield, explains David Hooker from the University of Guelph’s Ridgetown campus. Hooker and his associates set out to identify potential management strategies that farmers could use to improve crop yield and quality in spring-harvested corn.

There has been limited research into how to manage corn with the explicit intent of overwintering for a spring harvest, Hooker says. One trial in Wisconsin during 2000 and 2001 comparing fall- and spring-harvested corn plots showed yield losses could vary considerably. For example, with heavy snow cover, losses were 38 to 65 per cent, compared to a winter with little snow when yield losses were only seven to 10 per cent. However, newer hybrids with the Bt trait and genetics for improved stalk strength may have the potential to improve standability over the winter, Hooker says.

In southern Ontario, the standard management practices for corn production consist of planting at a relatively high plant population (80,000 plants per hectare), applying a foliar fungicide only if there is justifiable disease potential, harvesting in the autumn when grain moisture is approximately 25 per cent or less, and drying grain down to 15.5 per cent using on-farm grain dryers or through commercial elevators.

A review of the literature revealed some possible strategies for reducing yield losses associated with overwintering corn. These included selecting a hybrid with superior stalk strength, selecting later maturing hybrids, planting at a reduced population (i.e. 60,000 plants per hectare or 24,000 plants per acre). Another possible management strategy is to apply a foliar fungicide around tasseling time, which has been shown to delay leaf senescence and improve stalk strength, which can contribute to improved standability.

Field experiments were initiated to compare the effects of hybrid maturity, plant population, foliar fungicide application and harvest timing on grain yield and standability. Field experiments were initiated in 2009 and 2010 at five separate locations in southern Ontario near Belmont, Ridgetown and Lucan. Of the three locations, Lucan usually receives more snow because it is in the snowbelt region of southwestern Ontario, leeward of Lake Huron. Researchers compared spring versus fall harvest, plant populations (60,000 or 80,000 plants per hectare), with and without an application of Quilt foliar fungicide, and three corn hybrids with differing maturities. The parameters observed were stay-green in the autumn, lodging in spring, and grain yield, moisture and test weight of corn harvested in autumn and spring.

The results point to an overwintering management strategy for corn, which consists of planting at a reduced plant population (24,000 plants per acre) and spraying the crop with a foliar fungicide around tasseling. This strategy minimized yield losses across all hybrids by between 3.5 per cent and 13.2 per cent at four out of five field locations through improvements in corn standability, compared to when the crop overwintered using a standard population and no fungicide application.

While lower plant populations resulted in better standability, it was usually at the expense of some grain yield, Hooker says. An economic analysis of the yield data in this study would be of value to growers, he adds.

Unfortunately, while the overwintering management strategy was an improvement over previous reports of yield losses, lodging was still at unacceptable levels at most locations. High winds, heavy snowfall and other adverse weather conditions can overwhelm any management strategy geared to help mitigate the risks associated with overwintering corn, Hooker says. “At the Lucan location, 100 per cent of the corn was lodged in the spring.”

The study did not look at the effect of overwintering corn on grain vomitoxin levels. Hooker would like to see this addressed in future research.

“Overwintering corn should be considered on a year- and field-specific basis,” he concludes. For example, overwintering may be considered if grain moisture is extremely high (greater than 34 per cent) in November, if drying costs are high, the corn is of inferior quality (the grade of corn can improve with a spring harvest) and if root and stalk strength are excellent.

“The practice of harvesting corn in the spring carries significant risk, mainly due to root and stalk lodging and reduced harvestability,” Hooker says. In areas where the winters are typically harsh, overwintering corn is a risky practice regardless of the management strategy deployed, he cautions. 

February 16, 2016  By Helen Lammers-Helps