Disease Guide
University-rated fungicide efficacy, pricing per acre, and spray timing for NCLB (Exserohilum turcicum). Based on Crop Protection Network 2025 data.
Northern corn leaf blight (NCLB) is a foliar disease caused by the fungus Exserohilum turcicum (teleomorph: Setosphaeria turcica). It is one of the most common and well-studied corn diseases in the northern U.S. Corn Belt. NCLB produces distinctive long, elliptical, cigar-shaped lesions that are gray-green to tan and typically 1-6 inches long.
The disease favors moderate temperatures (65-80°F), heavy dew, and high humidity. Lesions first appear on lower leaves and progress upward through the canopy. The fungus overwinters on corn residue, so continuous corn and reduced-tillage systems carry higher risk. NCLB tends to be more severe in the northern Corn Belt where cooler, wetter conditions persist through the growing season.
Yield losses depend heavily on when the disease reaches the upper canopy. If NCLB lesions are present on the ear leaf and above before R2 (blister), losses can exceed 30%. Each leaf above the ear contributes roughly 8-10% of grain yield, so protecting the upper canopy during grain fill is the primary goal of fungicide applications targeting NCLB.
Efficacy ratings from the Crop Protection Network 2025, based on multi-year university field trial data. Only products with tested ratings are shown — untested or not-listed products are excluded.
| Product | Mode of Action | NCLB Rating |
|---|
Source: Crop Protection Network 2025. Ratings reflect multi-year, multi-location field trial performance.
Efficacy ratings cross-referenced with real purchase prices. Products sorted by efficacy rating — best performers first.
| Product | NCLB Rating | Best $/Acre |
|---|
Prices as of early 2025 from AgChem, FBN, and Farmerceag. Actual pricing varies by geography, volume, and timing.
Apply at VT-R1. The optimal timing for NCLB control is VT (tasseling) through R1 (silking). This single-application timing provides the best protection for the upper canopy during the critical grain fill period when yield is determined.
Scout lower leaves starting at V10. NCLB lesions appear on lower leaves first and progress upward. Look for the characteristic long, elliptical lesions with gray-green coloring. The decision threshold for spraying is typically when lesions are present on the third leaf below the ear leaf or higher by VT.
Consider hybrid resistance. Many modern corn hybrids carry Ht genes that confer partial NCLB resistance. In hybrids with strong resistance scores, fungicide applications for NCLB alone may not be economical under moderate pressure. Check your hybrid's disease ratings — a hybrid rated 6+ for NCLB may not need fungicide protection except under very high disease pressure.
Most products work well. NCLB is well-controlled by nearly all modern fungicides. Most products rate Very Good or better. This means product selection for NCLB can be driven by price, convenience, and what other diseases you need to control simultaneously — particularly tar spot, which requires more specific product selection.
Efficacy ratings for all 26 products across 7 diseases, pricing from 3 suppliers, decision frameworks, and an ROI calculator.
View full guide →Search and filter 9,196 yield records from 867 university field trials by year, state, and crop.
Browse data →Fungicide ratings, pricing, and timing for tar spot (Phyllachora maydis).
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View guide →Fungicide ratings, pricing, and timing for common rust (Puccinia sorghi).
View guide →Fungicide ratings, pricing, and timing for eyespot (Aureobasidium zeae).
View guide →Based on Crop Protection Network 2025 data, the top-rated products for NCLB include Topguard EQ, Veltyma, Revytek, Miravis Neo, and Priaxor — all rated Very Good to Excellent. Most dual and triple-MOA premix products provide Very Good NCLB control. Even budget options like Folicur and Proline rate Very Good for this disease.
NCLB produces long, elliptical, gray-green to tan lesions on corn leaves that are typically 1-6 inches long and shaped like cigars. Lesions start on lower leaves and progress upward. Under humid conditions, you may see dark gray-green sporulation on the underside of lesions. Unlike gray leaf spot, NCLB lesions are not bounded by leaf veins and have smooth, rounded edges.
The optimal spray timing for NCLB is VT (tasseling) to R1 (silking). Scout fields starting at V10 for lesions on lower leaves. A fungicide is most justified when lesions are present on the third leaf below the ear or higher by VT, especially with susceptible hybrids. The key yield protection window is keeping the ear leaf and above healthy through R3 (milk stage).
NCLB can reduce corn yields by 30% or more when lesions reach the ear leaf before R2 (blister). Typical losses under moderate pressure are 5-15 bu/acre. The critical factor is how much of the upper canopy is affected during grain fill — each leaf above the ear contributes approximately 8-10% of grain yield. Early, severe infections that kill the upper 3-4 leaves can cause devastating yield loss.
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