Foliar Fungicides

  • Published: Friday, July 9, 2021

Foliar Fungicides
By Andy Luke, field specialist in agronomy

We are nearing the time in the growing season when foliar fungicides will be applied, and recent rain events have increased the likelihood that diseases will be present in area fields. Scout your fields to make effective applications this growing season.

In corn, 75 to 90 percent of the carbohydrates used in grain fill come from the ear leaf and leaves above that point, so protecting these leaves from disease is critical. While diseases such as southern rust blow into the area from southern states, allowing infection to occur on any leaf throughout the canopy, other diseases, such as gray leaf spot, overwinter on corn residue and produce spores that splash onto young corn leaves. As the corn grows, the disease works its way up the canopy to the vital upper leaves, where it can impact yield. Detecting overwintering diseases in the lower canopy can help with timely fungicide applications, preventing the disease from reaching the upper leaves.

Soybean fungicide trials conducted by the MU Certified Strip Trial program have shown an average yield increase of 1.5 bushels per acre when applied at the R3 (beginning pod) growth stage. This data comes from 33 tests across Missouri from 2018 to 2020. Treated strips also had significantly less disease pressure after applications.

Fungicides generally have an effective residual range from 14-21 days. Therefore, proper application timing is critical to receive the full fungicide benefit. For corn, research has shown that the greatest yield response occurs from applications made at tasseling or early silking (VT-R1). In soybeans, R3-R4 applications are recommended. It’s important to note that fungicides will not cure existing disease symptoms, but can slow or eliminate the spread.

While fungicides can protect yield in both corn and soybean fields, they should not be applied over every field. Some diseases, including frogeye leaf spot in soybean, have developed resistance to commonly applied fungicides. Remember that for a disease to be present, there has to be a susceptible host, the pathogen, and a favorable environment. If you have planted a resistant variety or if weather conditions aren’t conducive to disease development, it’s unlikely that fungicide applications will increase yields enough to be economically viable.

Writer: Andy Luke

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