Controlling leaf diseases in seed corn in 2001
The wet spring has been very favorable for pathogens and we can already see leaf diseases developing on corn. Fortunately, the most common leaf disease at this point seems to be holcus spot, which rarely, if ever, causes economic damage. Fungal leaf diseases are also beginning to appear, with anthracnose and eyespot especially evident. Now is the time to be looking for these early symptoms of leaf diseases in seed corn. Eyespot (Aureobasidium zeae), common rust (Puccinia sorghi), gray leaf spot (Cercospora zeae-maydis), and northern leaf spot (Bipolaris zeicola, also known as Helminthosporium carbonum) are diseases that can cause losses in seed corn production and sometimes need to be controlled with a fungicide application. Seed corn presents different challenges (and opportunities) when it comes to disease management.
The benefits of foliar fungicides on seed corn have been researched for a number of years at Iowa State University. Protecting susceptible inbreds with a fungicide has proven to be very profitable. Fungicide options have been changing, and this year is the first year that Quadris (Syngenta Crop Protection) is labeled for corn. Quadris offers some advantages over the standard product, Tilt. Generally, Quadris provides superior disease control compared with Tilt and yield increases that are similar or better than those we have seen with Tilt. Three other fungicides may be used on seed corn; they differ in their type of activity (contact versus systemic), spectrum of disease control, and application requirements. See the table for comparisons of the fungicides most commonly used on seed corn. For now, guidelines for foliar disease control are based on scouting, relative susceptibility of the seed parent inbred, and weather considerations. We are currently researching methods to predict gray leaf spot so that fungicide application decision-making can be improved. In general, the most profitable results occur when sprays are initiated prior to detasseling. Attempts to stop an epidemic will likely be unprofitable if the first fungicide application is made after detasseling. The following guidelines should be followed for the control of leaf diseases in seed corn:
Always check the label of any pesticide to confirm that it is registered for the intended use and to be sure that all label requirements are fulfilled.
aIf Tilt is applied after silking, crop residue cannot be fed to livestock. This article originally appeared on pages 119-120 of the IC-486(15) -- June 25, 2001 issue. Updated 06/24/2001 - 1:00pm
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