Missouri Study Finds R3 Fungicide Often Costly for Soybeans

By Blake Jackson

A seven-year study conducted by University of Missouri Extension indicates that many soybean farmers in Missouri may be losing money by applying fungicides at the R3 growth stage.

Since 2018, MU researchers have conducted on-farm strip trials across the state to assess the impact of fungicide use. While some applications occasionally improved yields, the increases were generally too small to cover the costs.

On average, yields rose by just 1.8 bushels per acre. At a soybean price of $10.20 per bushel, that amounts to roughly $18.36 in additional revenue. With application costs ranging from $30 to $40 per acre, most farmers ended up losing about $15 per acre.

“Foliar disease pressure in Missouri is often low,” said lead researcher Mandy Bish, a plant pathologist with MU Extension. “That means applying fungicides for diseases isn’t typically justified and in some cases, it even reduced yields.”

The trials showed considerable variability. In the best-case scenario, one field gained 12 bushels per acre, while in the worst case, yields dropped by nearly three bushels.

Preliminary models suggest that weather may influence results, with rainfall within 48 hours of spraying potentially enhancing effectiveness.

Beyond economic considerations, the research highlights long-term benefits. Fewer unnecessary fungicide applications can slow the development of resistance, preserving these products for when they are truly needed.

“Decreasing unnecessary applications helps protect the effectiveness of these products long term,” Bish said.

Some farmers found the results surprising. One participant admitted, “I thought these results were crap when you first shared them at a field day. I own my sprayer, was leaving the field day to go spray my beans, was mad, and set up a strip trial myself. My results were almost identical to what you presented.”

For Missouri soybean growers, the takeaway is clear: fungicide applications at R3 may sometimes provide a benefit, but more often, they do not. Researchers encourage farmers to assess field conditions carefully and make informed decisions before using fungicides.

The study reinforces the importance of data-driven management decisions, helping farmers save money, reduce resistance, and make choices tailored to their fields.

Photo Credit: istock-fotokostic