Because of cool, wet conditions between late April and the third week of May, Ohio’s corn and soybeans are only just emerged in some fields and not even out of the ground in others. However, both corn and soybean producers are contemplating adding fungicides to their management programs for this year’s crop.

Results from replicated fungicide trials conducted between 2006 and 2009 show very similar trends in terms of yield response across Ohio and across the Corn Belt. Corn hybrid yield response to foliar fungicides continues to be highly variable and unpredictable. Corn fungicide trials were conducted at four locations in Ohio (Western Research Station, near South Charleston; the Northwest Research Station, near Hoytville; the Snyder Farm, Wooster, and the ATI Research Farm in Apple Creek), providing a total of 25 trials for disease and yield comparisons. At each location, multiple hybrids with different levels of resistance to gray leaf spot and yield potential were planted, allowing for the evaluation of hybrid corn yield response to fungicides for a combination disease pressure, weather and hybrid scenarios. Most of the trials were planted no-till or reduced-till into fields previously planted with corn.

In all cases, foliar fungicides were applied between tassel and silk emergence (VT-R1) at label-recommended rates at 20 GPA, using a high-clearance spray. At the time of fungicide application, only trace amounts of foliar disease were observed on the lower leaves (well below the recommended fungicide application threshold), and disease levels remained low through the growing season at all locations.

Yields in the untreated checks ranged from 73.6 to 177.96 bu./acre, with an average of 109.8 bu., whereas in fungicide-treated plots, yields ranged from 68.19 to 188.49 bu./acre, with an average of 109.55 bu. Yield differences between treated and untreated plots (treated minus untreated) ranged from -16.70 to 10.53 bu./acre, with an average difference of -0.28 bu.

Similar fungicide trials were conducted by university researchers across the Corn Belt, with similar results. Depending on the fungicide, average yield differences between treated and non-treated were between -1.2 and 4 bu./acre when foliar disease severity was less than 5% and between 1.6 and 10 bu./acre when severity was greater than 5%.

Fungicide use remains most profitable when disease levels are high under susceptible conditions. Scout fields for disease before applying a fungicide. In addition to not always being profitable, the unnecessary use fungicides increase the risk of fungicide resistance, so when disease does occur these tools may not be effective. Monitor weather conditions to see if they are favorable for disease development. For gray leaf spot these are wet humid conditions during July and August. For northern corn leaf blight, these are cool, wet conditions. Drought conditions do not favor either disease.