Do Fungicide Applications Increase Yields? Scout Your Field Before You Decide.
There is considerable interest across the Corn Belt in applying fungicides to field corn. When corn prices were down below $2 a bushel in the past, it was easy to say “no” to fungicide. This growing season, the high price of corn and rising disease risk due to increased corn-after-corn acreage has many farmers considering fungicide applications to increase yields.
Before applying a fungicide to corn this season, it would be smart to know the resistance to foliar disease of the hybrid being grown. The most common foliar diseases are tar spot, common rust, gray leaf spot and northern corn leaf blight. Back in the mid-1990s, research demonstrated a single application of fungicide could be profitable; however, profitability was strongly influenced by gray leaf spot susceptibility. In other words, the chance of increased yield and making a profit was only likely for highly-susceptible hybrids. On intermediate and moderately-resistant hybrids, any yield benefit would not cover the costs of the fungicide application.
Many foliar diseases start on the bottom leaves of a corn plant and gradually move up the plant, depending on environmental conditions. Scouting the field can give us a very good indication of disease pressure in that field.
The best time to start scouting is now through tasseling. Look for disease development on the lower leaves of the corn plant up to, and including, the ear leaf. Remember: The ear leaf and leaves above that contribute 75 to 90 percent of the carbohydrates to grain fill. These are the leaves needed for protection. If disease is not present on the leaves below the ear leaf, a fungicide application may not be warranted. Continue scouting on a weekly basis.
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