Wet weather prompts warning about northern corn leaf blight

Northern corn leaf blight (courtesy BASF)

If above average moisture continues through June, growers should start scouting early for northern corn leaf blight (NCLB).

Rob Miller, BASF’s technical development manager for eastern Canada, says NCLB can appear as early as the 8-10 leaf stage in a wet season. Lesions appear on the lower leaves and move upwards, as the infection often takes place in the whorl. Lesions become noticeable once the leaf has fully emerged; emergence is occurring now in many Ontario fields.

Infections that occur prior to tassel have the greatest effect on yield. So Miller’s recommending early scouting, for the best control.

“Growers should start scouting soon, up until brown silks,” he says.

NCLB overwinters in corn residue, and spores are dispersed by rain. This year, Ontario has experienced above-average precipitation. After a stretch of dry weather during planting, rain moved in. It got the crop off to a decent start, but set up conditions for disease.

And that could be a problem. Miller says extended periods of leaf wetness and moderate temperatures (17°-27°C) favour NCLB.

As well, late planted corn is more prone to leaf diseases in general, because it flowers later in the season when nights are longer and moisture is present longer.

All of these conditions have him concerned.

“Hybrid selection, crop rotation and environmental factors will influence the disease,” he says. “Much of it will depend on the weather over the next six weeks.”

The outlook is discouraging. Albert Tenuta from the Ontario Ministry of Agriculture, Food and Rural Affairs has identified new races of NCLB that are overcoming the disease tolerance of the corn hybrids now on the market.

That points to the need for multiple modes of action, for control.

Miller says if NCLB is found in the field, and weather conditions are favourable for development, growers can use a foliar fungicide at tassel emergence to brown silks for the greatest return on investment. But, he adds, multiple modes of action are particularly important to help manage resistance.

Miller suggests producers first focus on fields with high yield potential, such as those with good fertility, adequate nitrogen and uniform plant stand. After that, target fields with susceptible hybrids, corn-on-corn rotation, or silage corn.

“Significant investment has already been made in the corn crop, so the real challenge is protecting that investment and maximizing yield potential,” says Miller. “The risk of NCLB may be higher this year, but if detected early, yield loss should be minimal.”

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Owen Roberts

Owen Roberts directs research communications and teaches at the University of Guelph, and is president of the International Federation of Agricultural Journalists. You can find him on Twitter as

@theurbancowboy

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