Integrated Crop Management

Controlling leaf diseases in seed corn in 2000

Now is the time to be looking for early symptoms of leaf diseases in seed corn. The dry conditions of the early season were not favorable for reproduction and spread of these fungi, but recent rains may be sufficient to initiate some infections. Seed corn presents different challenges (and opportunities) when it comes to disease management. Some unique features of seed production compared with grain production are as follows:

  1. high value per acre,
  2. a broader range of leaf diseases cause economic damage,
  3. a need to grow specific genotypes regardless of susceptibility,
  4. leaf loss due to detasseling, and
  5. more fungicide options.

Some of these features lead to a greater need for fungicidal disease control in seed corn compared with field corn. The benefits of foliar fungicides on seed corn have been researched for several years at Iowa State University. Protecting susceptible inbreds with a fungicide has proven to be very profitable.

Leaf disease problems in seed corn include gray leaf spot (Cercospora zeae-maydis), eyespot (Aureobasidium zeae), common rust (Puccinia sorghi), northern leaf spot (Bipolaris zeicola, also known as Helminthosporium carbonum), and northern leaf blight (Exserohilum turcicum).



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[1]
Early symptoms of gray leaf spot.


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[2]
Common maize rust.

For now, guidelines (listed below) for foliar disease control are based on scouting, relative susceptibility of the seed parent inbred, and weather. 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 spraying begins early in the season. Attempts to stop an epidemic will likely be unprofitable if the first fungicide application is made after detasseling.

There are four fungicides (chlorothalonil, copper, mancozeb, propiconazole) registered for use on corn for seed production. The fungicides differ in their efficacy against certain diseases and in their restrictions such as the preharvest interval and livestock feeding. Check the label to determine whether the fungicide may be applied, rates permitted, and for any restrictions of application. A recent change is that Tilt can now be applied up to 30 days preharvest (but forage and fodder may not be fed to livestock if Tilt is applied after silking). Tilt is the preferred product for gray leaf spot and eyespot control; it has protective and curative activity. Chlorothalonil (Bravo), copper salts (Tenncop), and mancozeb products (Manzate, Dithane, and Penncozeb) have protective activity only. These products are effective against rust, northern and southern leaf blights, and northern leaf spot. Penncozeb also specifies gray leaf spot control on the label. Some newer fungicides are being developed for corn, and they look very good, but are not yet registered.


Source URL:
http://www.ipm.iastate.edu/ipm/icm//ipm/icm/2000/6-26-2000/control2000.html