2019’s planting season crawl sparked a big question: When should I switch to short-season corn?

By Connor Lynch
Planting season 2019 was brutal and slow, and market economics, combined with bad weather, pushed many growers to plant shorter-season corn hybrids.

But short-season hybrids, in exchange for maturing earlier, come with a yield cost. Farmers need to be careful about when that trade-off is going to be in their favour.

Former OMAFRA employee and Maizex agronomy lead Greg Stewart was on hand at the SouthWest Ag Conference last month sharing some of the latest research on just how much yield potential growers are giving up by switching to shorter-season hybrids.

There’s an idea floating around out there that modern hybrids have largely closed the yield gap between short and long-season corn varieties. It’s not as big as it used to be, Stewart said. But it’s definitely not closed.

Ontario research trials going back 30 years suggest, on average, the yield loss (or gain) by dropping 100 CHU (corn heat units) or adding 100 CHU on a variety dropped from about 7.2 bushels per acre to 4.4 bu/ac. In other words, grow a 100 CHU higher variety, add 4.4 bu/ac of yield. Grow a 100 CHU lower variety, lose 4.4 bu/ac. That’s a spread of almost 9 bu/ac.

“That’s too much yield to ignore,” Stewart said. Even with added drying costs (since those higher CHU varieties tend to have higher moisture come harvest), those varieties come out ahead.

So what’s a farmer to do when spring is turning into summer but the corn still isn’t planted?

Based on a couple of case studies on Ontario farms, OMAFRA’s corn specialist Ben Rosser recommended that when you are going to be planting late, stick with a long-season hybrid as late as June 1. Hybrids can flex and can handle 10 per cent lower heat units, he said. But it isn’t enough to drop 100 CHU per week if planting is delayed after the initial window. Producers have to be even more aggressive than that.

In his three Western Ontario case studies, growers that cut back CHUs even more than the 100/week guideline after the target planting date had crops that didn’t make it to black layer before a killing frost. Three case studies aren’t enough data to draw firm conclusions, he cautioned, but they do suggest that when it does come time for growers to switch to short-season hybrids, you have to switch to even shorter season hybrids than you expected.