Mother Nature has been too generous with moisture this year in most of the Corn Belt states. It has hurt some crops but has been conducive to the development for diseases like Northern Corn Leaf Blight and Gray Leaf Spot. Some of the early planted corn has already been sprayed with foliar fungicides. Late planted corn is starting to pollinate. I have seen a lot of these two diseases during the last two weeks especially on corn after corn ground and have been asked by some farmers if these fungicides applications are economical at the current prices. Some of the guidelines for economic thresholds are given below:
• Corn needs to be protected from leaf diseases mostly during the grain-fill period. Depending on relative maturity of the hybrid, 45 to 55 days, are needed from pollination to physiological maturity or Black Layer.
• We need to protect leaves above the ears which produce most of the grain yield. Foliar fungicides provide protection for only 3 to 4 weeks, depending on the fungicide and adjuvant used.
• It costs $30 to $40 per acre to have fungicides applied. At current grain prices, you would need about 10 B/A yield increase to break even. So, make sure you apply fungicides after all silks are brown and only if disease starts to move on the ear-leaf and above.
• Some farmers are thinking about adding CoRon to the fungicide as a source of supplemental Nitrogen if their fields showed N-deficiency symptoms due to too much rain and flooding.
• Tests conducted by the university researchers indicate it is not cost effective to apply fungicides as a preventive measure without the presence of the diseases. However, some newer chemicals with systemic qualities may be available.
• Realize that fungicides do not protect your crops from diseases caused by bacteria like Goss’ Wilt and viruses.
• Hybrids with good tolerance to Northern Corn Leaf Blight and Gray Leaf Spot are available. Make sure to check with your Seed Consultant Rep before you order seed for next year.