Is fungicide the right move for corn and soybeans in 2020?

Alexandra Knight

By Alexandra Knight, Ph.D., Field Agronomist, Pioneer

Late season fungicide and insecticide applications to corn and soybeans is a management decision growers will be making rather quickly but, does it appear this year will pay?

In many parts of Ohio, 2019 left fields unplanted. In many cases, cover crops were planted to preserve mycorrhizal fungi. While this left an opportunity for beneficial organisms to thrive, it also provided an opportunity for insects and diseases to maintain a home. This combined with the mild winter, would lead us to suspect 2020 to be a strong year for both insects and disease.

In both corn and soybeans, the leaves serve as “solar panels” to capture sunlight and turn that sunlight into sugar to produce grain. When leaves remain healthy and undamaged more sugar can be produced and ultimately more yield obtained.

When fungicide applications occur, the leaf is protected from further disease development for a period of approximately 2 to 3 weeks. Fungicides won’t add bushels. Instead the fungicide will work to protect yield loss due to plant diseases. Fungicides can also improve harvest standability by allowing plants to remain healthy rather than cannibalizing stalks at the end of the season. Additionally, the use of a fungicide product with multiple modes of action fungicide is beneficial. The strobilurin family of fungicides provides staygreen power.

Insecticides will have a similar window of protection and can be included with a foliar fungicide application. Preventing feeding will serve an additional purpose as insect injury frequently allows for an entry point for crop diseases.

In general, it would appear disease and insect pressure is at greater risk in 2020; however, scouting will be key in considering these applications. Prioritize those fields which had cover crops in 2019, those in no-till systems and corn-on-corn or soybean following soybean situations as these will be higher risk areas. Additionally, determine the disease ratings for your hybrids and varieties.

In corn hybrids you have planted, determine gray leaf spot (GLS) and northern corn leaf blight (NCLB) ratings as these are the prominent corn diseases encountered across Ohio. Hybrids with low resistance scores should be prioritized for fungicide applications. Another disease to scout for in corn will be tar spot. Because this disease is still relatively new to the Midwest, you will not likely find disease scores for hybrids. University and industry data both show a benefit with the use of fungicide in the presence of tar spot. In the same way you look at scores for hybrids on corn diseases, soybean varieties with low tolerance to frogeye should be prioritized on the soybean side. Insect scouting will also be key. This will help in selection of an insecticide targeting the pest you are seeing in the field.

The ideal time to apply fungicides in corn for maximum protection is near tasseling/silking (VT/R1). Pioneer has conducted corn fungicide trials from 2007-2018 showing a +7.4 Bu./A yield increase in corn at this timing. Carefully read product labels, as the use of adjuvants may cause crop and ear damage. In soybeans, the ideal time has shown to be R3 (when pods are 3/16-inch long near the top of the plant). Pioneer soybean fungicide data has shown an average increase of +3.7 bushels per acre, which is maximized at the R3 growth stage. Research has shown that making this application late in R3 or even early R4 will be more beneficial than erring on the early side of flowering. The addition of insecticide can lead to an increased yield response in both corn and soybeans due to the additive effect of a fungicide + insecticide.

In cases where corn has high yield potential, and especially if susceptible hybrids were planted and disease is already present, fungicide applications at the proper time will be expected to provide a positive economic response both in terms of yield and stalk quality/standability. Soybean fungicide applications have shown to be profitable in the presence or absence of disease.


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