Fungicide Efficacy on Soybeans

As corn fungicide applications, you next decision might be if soybeans will need the same. While many of the decision making principles applied to corn apply to soybeans as well, the decision in soybeans is often more complex.

Disease pressure is an issue in soybeans. Crop Protection Network estimates put the average over the last five years (of all diseases: seedling pathogens/nematodes/fungal disease/viruses/etc…) at approximately $27/A. The foliar fungal complex portion of that total, however, is much smaller, complicating our decision making process – and making in-season scouting all the more important.There’s no need for a disease treatment if disease is absent!

Disease presence/absence is important because it plays a part in disease resistance management as well. Recently, Kansas joined the list of states with confirmed QoI fungicide-resistant strains of Frogeye Leaf Spot and Septoria Brown Spot. A 2022 survey confirmed resistance to the QoI class of fungicides in almost 80% of samples from Kansas soybean fields. Caution should be exercised when using fungicides to make sure multiple modes of action are used and products are used in such a way – and combined with other integrated disease management tools – to preserve future efficacy.

Can we get a yield response from fungicides applied in the absence of disease? Maybe, but with inconsistent results. An 18 treatment (non-treated check included) Iowa State study showed inconsistent results with no significant yield response. A nine-treatment study conducted by Kansas State University showed similar results: some products performed positively, while others were more neutral. Missouri strip trials (2018-2023) suggested a slightly less than two bushel per acre response. Foliar fungicide applications can result in good yields – but results will be inconsistent in the absence of disease.

If you are using a fungicide, use one that works! Efficacy of foliar fungicides for disease control is evaluated annually in trials by University Plant Pathologists (see the 2024 results on the Crop Protection Network site: https://cropprotectionnetwork.org/publications/fungicide-efficacy-for-control-of-soybean-foliar-diseases ). Check them out as you choose a product.