Careful Monitoring of Crop Growth Stages Helps Maximize the Benefits of Fungicide Treatments.
Penn State Extension specialists are reminding corn and soybean producers to rely on field scouting and disease risk assessments before applying foliar fungicides this growing season.
The guidance comes after Pennsylvania recorded its earliest confirmed case of tar spot in corn in June, an eastern part of the state when the crop was between the V9 and V10 growth stages. Tar spot has also been reported in several other states.
Extension experts Paul D. Esker, Alyssa Collins, and Adriana Murillo-Williams recommend using an integrated pest management strategy instead of making preventive fungicide applications without evaluating field conditions.
Growers are encouraged to monitor crop development, scout fields regularly, and consider factors such as hybrid selection, crop rotation, and tillage practices before deciding whether a fungicide application is necessary.
For soybean production, research continues to show that the ideal time for a foliar fungicide treatment is the R3, or beginning pod, growth stage. Multi-state studies, including research from Ontario, found that R3 applications increased yields by an average of 1.64 bushels per acre.
The greatest yield improvements occurred in fields planted by May 21 and during seasons with above-average rainfall. However, when disease pressure remained minimal, fungicide applications often failed to generate enough additional yield to offset treatment costs.
In corn, the strongest yield response is generally achieved when fungicides are applied during the VT to R1 growth stages, spanning tasseling through silking. Protecting the ear leaf and upper canopy during this period helps maximize photosynthesis and supports kernel development.
Penn State also encourages growers to scout carefully throughout July for gray leaf spot and northern corn leaf blight in corn, as well as frogeye leaf spot in soybeans. Because fungicide applications typically cost between $30 and $40 per acre, producers should carefully weigh disease pressure, crop history, resistance levels, and market conditions before making an investment.
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