Northern Corn Leaf Blight
Symptoms - Early
- Early lesions are gray-green and elliptical, beginning 1 to 2 weeks after infection.
- In a susceptible reaction, fungal sporulation will begin within a few days.
Symptoms - Fully Developed
- Lesions become pale gray to tan as they enlarge to 1 to 6 inches or longer.
- Distinct cigar-shaped lesions unrestricted by leaf veins make Northern Corn Leaf Blight (NCLB) one of the easiest diseases to identify.
- Under moist conditions, lesions produce dark gray spores, usually on the lower leaf surface, giving the lesions a "dirty" appearance.
- As many lesions enlarge and coalesce, entire leaves or leaf areas may be covered.
- Heavy blighting and lesion coalescence give leaves a gray/burned appearance.
- Caused by Exserohilum turcicum (previously classified as Helminthosporium turcicum), a fungus found in humid climates wherever corn is grown.
- Survives in corn debris and builds up over time in high-residue and continuous corn cropping systems.
- Favored by heavy dews, frequent showers, high humidity and moderate temperatures.
- Spores are spread by rain splash and air currents to the leaves of new crop plants in spring and early summer. Spores may be carried long distances by the wind.
- Infection occurs when free water is present on the leaf surface for 6 to 18 hours and temperatures are 65 to 80 F.
- Infections generally begin on lower leaves and progress up the plant, but infections may begin in the upper plant canopy when spore loads are high.
- New NCLB lesions can produce spores in as little as one week, allowing NCLB to spread much faster than many other corn leaf diseases.
Impact on Crop
- Infections by NCLB can occur at any growth stage, but plants are more susceptible after pollination.
- Yield losses may be caused by:
- decreased photosynthesis resulting in limited ear fill
- harvest losses if secondary stalk rot infection and stalk lodging accompany loss of leaf area.
- Yield losses are most severe when NCLB infects corn plants early and progresses to the upper plant leaves by pollination or early ear fill.
- If ear development outpaces disease progression, yield losses will be lower.
- Hybrid selection (see more below)
- Crop rotation to reduce previous corn residues and disease inoculum
- Tillage to help break down crop debris and reduce inoculum load
- Fungicide application to reduce yield loss and improve harvestability
- Consider hybrid susceptibility, previous crop, tillage, field history, application cost, corn price
- Commonly used fungicides include Headline, Quadris, Quilt, PropiMax EC, Stratego and Tilt
- Pioneer researchers select for resistant parent lines and hybrids in multiple environments where NCLB pressure is consistently high year after year.
- Pioneer hybrids are rated for NCLB resistance and ratings made available to customers.
- Most hybrids are rated from "3" to "6" on Pioneer's 1 to 9 scale, where 9 indicates highly resistant.
- Growers should choose hybrids rated a "5" or "6" for fields at risk of NCLB infection.
- Two types of resistance are available in hybrids:
|Multigenic Resistance||Single Gene "Ht" resistance
|more stable over time
||may be overcome in time
|reduces number of lesions on a leaf
||delays spore production, limits sporulation