Fungicide Decisions Should Be Based on Disease Risk

By Blake Jackson

Penn State Extension specialists are encouraging growers to carefully assess disease pressure before making foliar fungicide applications in corn and soybeans this season.

The recommendation follows the state's earliest recorded detection of tar spot in corn, reported on June 24 in an eastern Pennsylvania field where corn had reached the V9-V10 growth stage.

According to Penn State experts Paul D. Esker, Alyssa Collins, and Adriana Murillo-Williams, fungicide decisions should be guided by integrated pest management principles rather than routine applications.

Experts advise producers to identify disease risks, monitor crop growth stages, scout fields regularly, and consider cultural practices such as hybrid selection, crop rotation, and tillage before choosing a fungicide.

For soybeans, the preferred timing for foliar fungicide applications is the R3, or beginning pod, growth stage. Research conducted across multiple states and Ontario found that fungicide treatments applied at R3 produced an average yield increase of 1.64 bushels per acre.

Yield benefits were greatest when soybeans were planted by May 21, and growing conditions included above-average rainfall. When disease pressure remained low, however, the economic return from fungicide applications was often limited.

In corn, studies consistently show the greatest yield response when fungicides are applied during the VT-R1 growth stages, from tasseling through silking.

Protecting the ear leaf and upper canopy during this period helps maintain photosynthesis and supports grain development.

Although these applications often require specialized equipment or aerial services, they generally provide the highest return when only one fungicide treatment is planned.

Extension specialists recommend intensive scouting throughout early and mid-July for diseases such as gray leaf spot and northern corn leaf blight in corn, along with frogeye leaf spot in soybeans.

Crop resistance, previous crop history, residue levels, and current market prices should all be considered before investing in fungicide applications.

With treatment costs reaching $30 to $40 per acre, growers should ensure disease risk and expected yield benefits justify the expense before proceeding.

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