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What is the best timing for corn fungicide applications? Studies have shown that the economic return from a fungicide application is usually greater when fungicide use is based on the presence of a foliar disease. The exact yield response to a fungicide treatment cannot be predicted with certainty due to different types of crop stress and crop genetics. In corn, fungicides applied from tasseling to early silking may have the best possibility for economic return.
Application of fungicides at V5-V7 growth stages in corn appears to be an attractive option; the corn is small enough to travel through and often we are already making that trip to apply herbicide anyway. Including a fungicide application at this stage would prevent the hassle of booking and paying a custom applicator later in the season, right? This scenario has been studied by university plant pathologists across the country for several years. However, according to Alyssa Collins, Director of the Southeast Agricultural Research & Extension Center at Penn State, “in the majority of studies, we have found no significant yield benefit to a fungicide application at this early vegetative timing.” Collins adds that, aside from the added expense, applying a fungicide early in a situation where it is not really needed could encourage fungicide resistance in that field.
According to Collins, there are many reasons why fungicide application is favored around the start of corn reproductive stages: (1) The foliar diseases of highest concern are favored by the warm temperatures and high humidity found within the corn canopy at this stage. (2) The plant leaves that contribute most to grain fill are not yet formed at early vegetative stages, therefore they cannot be protected by an early fungicide application. (3) The fungi that cause diseases like gray leaf spot (GLS) and Northern corn leaf blight (NCLB) reside in crop residue, but require time and favorable conditions to sporulate and spread upward through the plant canopy to upper leaves.
While application at growth stages VT-R1 helps protect critical foliage at a critical time, it can pose a challenge because of the specialized equipment like a highboy or aerial application needed. Collins notes that, “if a farmer is only going to make one fungicide application, this should be the one, as it traditionally provides the biggest bang for the buck.” In some high disease pressure situations, farmers have had good results with a second treatment two to three weeks behind a VT application. However, the pre-harvest interval must be considered, especially when chopping corn for silage.
Because corn disease risk is a culmination of many factors, there may be situations in which an early season application can help preserve yield potential. Collins advises that the more factors at play, the greater possibility for realizing a benefit from fungicide at any timing. Factors can include: