By Connor Lynch
Northern corn leaf blight is the foliar corn disease to look out for in 2016 in Ontario, according to OMAFRA field crop pathologist Albert Tenuta.
The disease hits hard, and can cause losses as high as 45 bushels an acre if unchecked. In 2015, OMAFRA surveyed 181 fields across Ontario; 176 fields had incidence of the blight. “In Eastern Ontario, it ranges in our surveys. Anywhere from 75 to 90 per cent of the fields had northern corn leaf blight.”
The damage the fungus deals is largely in terms of yield, and since it doesn’t make a crop unfit for consumption, farmers need to decide whether or not paying for the fungicide is going to be worth it.
The blight has become a bigger problem in the last 10 to 15 years because it’s arriving earlier in the season. It used to show up after pollination and its impact on yield was much smaller. Now it’s here before pollination and over a season can wreak havoc. The blight hits the photosynthetic tissue on the plant hardest, reducing its ability to feed itself. That can stress a plant to the point where it cannibalizes itself for energy, which can cause stalk rot or other diseases.
“First thing is farmers need to assess their risk,” said Tenuta. Fortunately for a grower with 1,000 acres of corn, you don’t need to inspect every leaf. Farmers simply need to check off some of the major risk factors for the disease for their fields, to find out which are going to be most likely to develop the disease. Areas to watch are “where you’ve got hybrids that are more susceptible, where you’ve got corn on corn, (and) where you’ve got more residue on the field,” Tenuta said.
The key factor is timing. Farmers should be looking at their crop shortly before tasseling time, in early to mid-July. High-risk fields are likely to already have the blight at that point, said Tenuta. Tenuta recommends going out with a sharpie marker, and marking any lesions, then checking to see if they are growing.
And even if the disease does poke its head up, Tenuta doesn’t recommend automatically reaching for the fungicide sprayer. If it hits later in the season, the disease won’t have as big an impact on yield. The fungus also relies on the weather. Its ideal conditions are cooler temperatures and plenty of precipitation. A hot, dry summer will curtail its growth.
Growers who find the telltale cigar-shaped, tan lesions on their corn leaves should also take a look at where on the plant they are. Lesions on the upper leaves mean the blight blew in from somewhere else, whereas lesions on the lower leaves probably means that it was in your field, gestating over the winter in the corn residue.
And it’s bad news if the blight is on the lower leaves. “That’s the worst case scenario.”
Farmers should also be looking out for black spots in the lesions. Those mean the fungus is releasing spores.
Fortunately, said Tenuta, the commercially-available fungicides are very good at containing the blight.
The disease has been on the increase for the same reason as any other disease, said Tenuta. “The pathogens adapt. Whether that’s bypassing genetic resistance (or) developing fungicide resistance, that’s a natural process.”
But there are human efforts to push back. The Grain Farmers of Ontario have launched a study to research the blight, and federal research is taking place to combat the genetic advancements of the blight.
