Northern corn leaf blight (NCLB) is caused by the fungus Exserohilum turcicum and may be found in areas with moderate temperatures (65 to 85 °F) and high humidity. Yield losses as high as 30% to 50% have been reported when lesions are present on upper leaves at silking.1 Infected corn plants can be predisposed to stalk rots, and grain and silage quality and yield may be reduced.
The characteristic symptom of NCLB is cigar-shaped lesions that are gray to tan colored and one- to six-inches long on the leaves (Figure 1). As lesions mature, they turn tan and develop distinct dark areas of fungal sporulation. NCLB can occur at any growth stage, but the disease progresses more rapidly after pollination. Lesions first appear on lower leaves and move upwards as the disease progresses. On severely infected plants, the lesions can become so numerous that the leaves are eventually destroyed. Late in the season, plants may look like they have been killed by an early frost. Lesions on products containing resistance genes may appear as long, chlorotic, streaks, which can be mistaken for Stewart’s wilt or Goss's wilt.1
E. turcicum overwinters in and on corn debris. During warm, moist weather in early summer, new conidia are produced on the old residue. Conidia are then spread by wind and rain to the lower leaves of young corn plants. Conidia are produced abundantly in lesions on susceptible plants and are responsible for secondary spread within and between fields. The infection process begins when water is present on the leaf surface for 6 to 18 hours and when night temperatures are moderate.2
Good management practices include selecting corn products with good NCLB resistance and excellent yield potential. A combination of crop rotation for one to two years followed by tillage is recommended to prevent disease development. Rotating to a non-host crop can reduce NCLB levels by allowing the corn debris on which the fungus survives to decompose before corn is planted again. Burying residue may help reduce infection levels by decreasing the amount of primary inoculum available in the spring. In no-till and reduced tillage fields that have a history of NCLB, a two-year rotation away from corn may be necessary. Good soil fertility should be maintained to help minimize plant stress and control weeds, insects, and other diseases.
Fields should be scouted around V14 growth stage (prior to tassel emergence) to determine disease pressure. Fungicides applied from tasseling to early silking tend to have the best possibility for economic return. Before deciding to apply fungicides, consider costs involved as well as predicted weather conditions.
1Salgado, J.D., Schoenhals, J., and Paul, P.A. 2016. Northern corn leaf blight. Ohio State University Extension. PLPATH-CER-10. http://ohioline.osu.edu/.
2Robertson, A. 2009. Goss’s wilt and northern corn leaf blight showing up in Iowa.
3Carson, M.L. 1995. A new gene in maize conferring the “chlorotic halo” reaction to infection by Exserohilum turcicum. Plant Disease Vol.79: 717-720. Iowa State University Extension. http://www.extension.iastate.edu/.
4Wise, K. 2011. Northern corn leaf blight. Purdue University Extension. BP-84-W. http://www.extension.purdue.edu/. Web sources verified 07/27/18 140620080101 072718TAM