During the previous several growing seasons Gray Leaf Spot (GLS) and Northern Corn Leaf Blight (NCLB) developed in some corn fields, affecting yield and stalk quality. You might ask; “Will these diseases be a problem next year?” The answer to this question depends on several factors.
The fungi that cause the development of these diseases overwinter on crop residue. If GLS and NCLB developed in 2016, the fungus will be present on residue in 2017. The development of these diseases also depends on environmental factors. Warm, humid weather favors growth of GLS and NCLB. Periods of heavy due, fog, or light rain will provide the needed conditions for these leaf diseases to develop. For either GLS or NCLB to become a problem in 20127, the fungi need to be present in the field in addition to favorable weather conditions. Fortunately, producers can make some management decisions to hinder the growth of GLS and NCLB and lessen their impact should they develop:
1. Crop Rotation: Research shows that crop rotation is one of the most effective ways to mitigate problem diseases.
2. Plant Resistant Hybrids: Hybrids with stronger disease resistance will not be affected as much as those susceptible to disease—talk to your seedsman or agronomist about resistant hybrids.
3. Till Crop Residue: Clean tillage will help break down crop residue, reducing the chance GLS or NCLB will become a problem.
4. Fungicides: Fungicides are recommended for GLS on susceptible hybrids where the disease pressure is high.
The best way to determine if disease is developing is to scout fields; recognize the environmental conditions that will contribute to disease growth/spread and know how to identify diseases. NCLB symptoms are brown or tan cigar-shaped lesions, ranging from one to six inches in length. GLS symptoms are tan or gray rectangles with parallel or straight sides, ranging from half and inch to four inches in length. When scouting, make sure to take a pocket field guide along — they are a great resource for identifying problems and determining management options.