EXTENSION REPORT

Fungicides on Corn

This is a good opportunity for a good crop consultant.  There were nearly 300,000 acres of corn planted in Alabama this year.  Fungicide use on corn is becoming more popular as corn acres are going up, corn prices are going up and the industry is providing more information on the use of fungicides on corn.  Anyone who has used fungicides on fruits, vegetables or peanuts and seen the results it only stands to reason that fungicides should work well on corn also.  Before making the decision to spray there are several important factors to consider. 

Know your corn hybrid and its disease resistance package.  Some hybrids have a very good disease package and others do not.  Knowing your hybrid is very helpful in this decision.  Some of the top yielding hybrids are weak on disease resistance and may benefit by a fungicide. 

Know your corn diseases.  There are many diseases on corn, but only three that typically affect us in South Alabama.  The first is Southern Corn Leaf Blight.  This disease is present almost every year.  The symptom is tannish brown lesions on the leaf.  This disease does not usually cause significant yield loss.  Occasionally in wetter years we also have the Northern Corn Leaf Blight.  The lesions of NCLB are more chocolate colored than tan.  The second disease is Common Rust.  This disease is found where ever corn is grown.  Cinnamon brown rust pustules can be found on both the top and bottom side of the corn leaf.  The disease even though common does not cause significant yield loss.  The third disease is Southern Rust.  It can be a very serious problem.  Corn hybrids without resistance will take losses from 10 to 20 bushels and greater.    Fortunately Southern Rust is not as common here as Common Rust.  It usually occurs about 2 out of 10 years in South Alabama.  Southern rust is more common in tropical and subtropical regions of the world.  It likes warm humid weather.  Symptoms of Southern Rust are very similar to those of Common Rust.  At the early stages it is very difficult to tell the difference.  As the disease progresses it becomes more identifiable.  It can be distinguished by the pustules.  Southern Rust pustules are light cinnamon brown to orange (much more orange than Common Rust) and more densely scattered on the upper side of the leaf.  Southern Rust usually does not come into our area until later in the season.  If Southern Rust does come early and is present it would most definitely pay to spray a fungicide.  University specialists based on research conducted in Georgia and Mississippi are saying that in the absence of Southern Rust there would be very little benefit to spraying.     

There is some data that indicates that there is a plant health yield enhancement from the Strobilurin chemistry in some fungicides.  This data is showing a 5 % yield increase in yield even in the absence of Southern Rust.  This is very likely to be the case, however, UGA and MSU are conducting further research before making their University statement. 

Fungicides labeled:  To my knowledge the fungicides labeled for corn are the same fungicides as for wheat.  They include Headline, Quadris, Quilt, Stratego, Tilt and Propimax.  See the labels for use and rate. 

The application timing is another factor.  From early tassel the first labeled application through physiological maturity is around 60 days.  If your first spray is at tassel and it protects the corn for 20 days there are 40 days left when the corn is unprotected.  It would take three sprays to keep your crop totally protected.   Growers need to know if the disease is already present or not.  And also base their application on the future weather data and possibilities of the diseases coming.

In summary, the factors to consider are:  Know your corn hybrid. Know your corn diseases and whether they are present in your field or the area.  Know your fungicides and time of application.  Know your corn crop potential.  Corn with a good yield potential is more likely to pay to spray.  Corn planted behind corn typically is more prone to disease and may benefit by spraying.  When diseases are present spraying enhances corn stalk strength and helps prevent lodging.  Know your stink bug levels in your field and considering if you need to be spraying for them also.   

Email address: rpetcher@aces.edu
Phone number: 937-7176 or 943-5611, 928-0860, ext. 2222

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.