Northern corn leaf blight management tips

JOHNSTON, Iowa — Northern corn leaf blight has increased in prevalence over the past decade-plus across the Midwest.

Northern corn leaf blight can cause as much as 30% yield loss if it develops before or during the tasseling and silking phases of corn development.

Yield losses are most severe when NCLB infects corn plants early and reaches the upper leaves by the beginning of ear fill.

“It’s very typical for this pathogen to form brown, cigar-shape type lesion. It usually starts on the bottom of the plant and then moves upward,” said Adam Owens, Pioneer field agronomist.

“We really want to protect the ear leaf and the upper third of our crop canopy for the maximum plant health.”

While it can be found wherever corn is grown, three main factors lead to NCLB infection: air temperature, high humidity and leaf wetness hours.

“NCLB really likes temperatures between 64 and 81 degrees, high relative humidity and at least six or more leaf wetness hours in a day,” Owens added.

Symptoms

Early NCLB symptoms appear as long, narrow, tan lesions that form parallel to leaf margins. The cigar-shaped lesions produce olive-green or black fungal spores when humidity is high, which can give the lesions a dark or dirty appearance.

Disease spores are spread locally by rain splash, where primary infections are produced.

Secondary spread occurs from plant-to-plant and field-to-field as spores are carried long distances by the wind.

It has also spread in recent years due to major weather events, especially hurricanes, which carry the organism from southern climates to North America.

Although infections generally begin on lower leaves and then progress up the plant, in severe NCLB outbreak years — that have high spore levels — infections may begin in the upper plant canopy.

Yield loss from NCLB occurs when lesions reduce the leaf area of the plant that carries out photosynthesis. The more lesions on a plant and the earlier in the season the lesions develop, the greater the loss of photosynthetic area and the greater the potential yield loss.

Management

Effective NCLB management practices include selecting resistant hybrids, reducing corn residue in the field, timely planting and applying foliar fungicides.

Decisions to use a fungicide should be based on the disease risk factors of the field, including hybrid susceptibility, cropping sequence, tillage system, location, disease history, yield potential, the price of corn and expected weather during reproductive development.

Pam Pflugradt, Corteva Agriscience territory manager, recommends Aproach Prima fungicide for NCLB control.

“You’ll want to use 6.8 ounces per acre. That will give you a good 21-day residual,” Pflugradt said.

“The one thing we caution against is do not use any adjuvant that includes a non-ionic. That could cause some ear development issues. So, just stay away from that, otherwise you can put something in there if you would like.”