No. 3 Article 6/April 23, 2010

Fungicide Applications to Corn at Early Growth Stages

Over the winter, I was repeatedly asked about the value of applying foliar fungicides to corn at early growth stages (V5-V6), a timing being promoted by some companies. This timing would provide some advantages as far as the ability to apply fungicide with a ground applicator and to tank-mix with a post┬Čemergence herbicide. However, it may not provide much advantage in disease control, which is the most important reason to apply a fungicide. Most of the important foliar diseases frequently observed in Illinois would either not be present at the V5-V6 stage or, if present, would be at extremely low levels.

Unfortunately, few replicated field research trials have been conducted to evaluate these early-growth-stage timings of foliar fungicides on corn. I recently sent a data request to colleagues at other universities so that a larger set of results could be summarized, but only a few in the north-central U.S. had done such evaluations (Figure 3).

Figure 3. Summary of yield responses of corn with Headline fungicide applied at the V6 or VT-R1 growth stage. (Data courtesy of P. Esker, University of Wisconsin; E. Nafziger, University of Illinois; K. Wise, Purdue University; A. Robertson, Iowa State University; and T. Jackson, University of Nebraska).

Of products currently registered on corn, only Headline fungicide (BASF) had been evaluated at these early timings in more than two trials. In these trials conducted across Illinois, Indiana, Iowa, Nebraska, and Wisconsin, yield responses to Headline (applied at either V6 or VT-R1) varied by trial. Yield responses of at least +10 bushels/acre were observed in one of the eight trials with V6 applications and in three of the eight trials with VT-R1 applications. The overall average yield response across all trials was 1.5 bushels/acre with V6 applications and 8 bushels/acre with VT-R1 applications. Level of disease pressure varied by trial and location; for instance, a high level of southern rust was present in some of the Nebraska trials.

Overall, the VT-R1 timing appears to be more advantageous for disease control and yield response compared to the V6 application. The biggest yield responses with foliar fungicides on corn will be observed in fields that have the highest risk of foliar diseases. Disease risk increases with more susceptible hybrids and in corn-on-corn situations.--Carl A. Bradley

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