Dave Nanda read the Aug. 8 story about foliar fungicides in corn. It urged farmers to spray fungicides earlier in the future than many did in the past to get the most bang for their buck invested in fungicides.
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Nanda, a retired plant breeder and now a crops consultant, has a different opinion than those expressed in that article. While it may be late enough that the subject is academic this year, he believes it’s a valid topic for discussion in the future.
“Even with low corn prices and generally lower disease pressures this year, each situation is different,” he says. “But if disease pressure in a field is heavy and diseases like northern corn leaf blight and gray leaf spot are dominant and moving to the ear leaf and above, we need to apply foliar fungicides as a rescue treatment. It is not a preventative treatment.”
Differences among hybrids is very important. Some hybrids are definitely more disease-tolerant than others.
Other things you need to know about a field when making fungicide application decisions include hybrid relative maturity, date of planting, previous crop, whether tillage is no-till or conventional, and whether cover crops are used.
Local environmental conditions can play an important role in disease development and spread, Nanda says. “While scouting a cornfield in southeast Indiana several weeks ago when corn was pollinating, I saw a lot of gray leaf spot on some hybrids from different seed companies.
“The yield loss due to leaf diseases may not be only the direct effect of loss of photosynthetic tissue, but also the predisposition of the plants to stalk rots and lodging, followed by ear rots and lower test weight," Nanda explains.
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“The timing of fungicide application is very important. We know from our own studies at Facemire Farms near Edinburgh several years ago that we can hurt the crop by applying fungicides before the pollination process is completely over," he says. "You don't want to wait too long after the silks are pollinated and start to turn brown, but you need to protect the upper leaves during the grain-fill period, which is about 50 to 60 days after pollination is over. Most fungicides won’t last that long.”