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Northern Corn Leaf Blight In Parts Of PA

By Beth K. Gugino
 
In parts of south central PA, Northern corn leaf blight is being observed in sweet corn.
 
 
Elongated tan lesions characteristic of Northern corn leaf blight on corn (Photo: Allison Robertson, Iowa State Univ.).
 
Elongated tan lesions characteristic of Northern corn leaf blight on corn 
 
Northern corn leaf blight symptoms are usually first observed on the lower leaves and the spread up the plant. The lesions are initially small, elliptical and gray-green in color. As the disease progresses the lesions will expand to 1 to 6 inches long, become tan in color and are not restricted by the leave veins. Eventually, the lesions will coalesce and cover the entire leaf. Under humid conditions, the lesions will produce dark gray spores on the lower leaf surface giving them a dusty appearance. A new lesion can produce spores in as little as one week under favorable conditions. The spores are then disseminated by rain splash to the leaves of nearby plants or they can be carried in the wind longer distances during storms. The greatest losses from NCLB occur when severe necrosis develops on the upper 2/3 of crop canopy by silking. The reduction in photosynthesis due to the necrosis results in reduced ear fill and when symptoms develop on the husks they appear older and are less marketable.
 
The crop should be scouted regularly, focusing on the lower leaves where symptoms develop first. Protectant fungicides like chlorothalonil can be applied when there are reports of NCLB in the area but symptoms have not been observed in the field. Good coverage is critical. NCLB specific fungicides include those in FRAC group 11 (strobilurins; e.g. Quadris and Headline) and FRAC group 3 (triazoles; e.g. Tilt). There are also a number of products that contain both FRAC groups (11 + 3; e.g.  Quilt and Stratego). Rotate between these FRAC codes and tank mix with a broadspectrum protectant for resistance management when symptoms are first observed in the field will help manage NCLB. PHIs vary between the products so read the labels carefully when the crop is near harvest. Also depending on the label, NCLB might be referred to as Helminthosporium leaf blight which is collectively refers to both Northern corn leaf blight and Southern corn leaf blight. For more information check out the upcoming August issue of the Vegetable and Small Fruit Gazette.
 

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