Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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July 5, 2007

July 5, 2007




To Spray a Fungicide or Not to Spray a Fungicide

There is a great deal of interest in spraying fungicides on corn this year.  Planes have started to fly already. There are several issues to remember and consider before “pulling the trigger.” First, remember the disease triangle, which states that in order for a disease to develop, three things must occur simultaneously:

1.     There must be a susceptible host.

2.     The disease pathogen must be present.

3.     The weather must be conducive for the pathogen to successfully infect the host.

Therefore, ask yourself the following questions:

1.     Does the hybrid have a poor or mediocre foliar disease resistance package?

2.     Is there reason to believe the pathogen is present, such as corn following corn with a great deal of residue on the surface or, in the case of the rusts, that it has blown in from the south?

3.     Is the weather and weather forecast / outlook conducive for the infection?  Most diseases like wet weather, with gray leaf spot and southern corn rust liking hot and humid weather while most of the other diseases like cool and wet weather.

The fewer “yeses” you have to the above questions, the lower is your likelihood of getting your money back.

Second, remember that most fungicides are effective for only 14 – 21 days.  There are 55 – 60 days between pollination and crop maturity.  Applying the fungicide too early or too late is a waste of money.  In 2005, generally the early fungicide applications were most beneficial (eastern Iowa excluded because of the drought) while in 2006, the later applications were most beneficial.  This difference was because of the different weather patterns in the two years.  So what is the best timing?  Remember that the goal is to protect the ear leaf and all leaves above the ear leaf.  Applying before the tassels are fully emerged means that the top leaves have not fully emerged and they will not be protected.  Once tassels are fully emerged, scout the field closely for evidence of leaf diseases, examining leaves from the top of the plants to the bottom of the plants.  If lesions are found on or above the ear leaf, or if lesions are found on several leaves below the ear leaf, the timing is probably about right for an application.

Emerson Nafziger, University of Illinois, wrote an excellent article on pages 117 – 118 of the June 29, 2007 Illinois Pest Management and Crop Development Bulletin,  They saw an average yield increase of 6.2 bu/A in the last 3 years of trials in spraying Headline on corn, which would not pay for the treatment with today’s corn prices. Alison Robertson, Daren Mueller, Carol Pilcher, and Kristine Schaefer wrote the first of two article on the subject on page 197 of the June 25, 2007 Iowa State University Integrated Crop Management Newsletter  The second article should be in the July 2, 2007 Integrated Crop Management Newsletter and posted at soon.




Midwest Strip Till Conference – July 31 9 a.m. to 3:00 p.m.



Organized by Research and Extension of Iowa State University, the University of Minnesota, the University of Wisconsin, and Hawkeye Community College. Manufacturers will demonstrate equipment for strip-tillage and associated operations, including auto-guidance systems and fertilizer injectors.  Researchers, farmers, and industry representatives will present the latest information on strip-tillage related topics, including equipment selection, fertility management, and guidance technology. Participants will review information booths all day, and lunch is available on site.  This program is free and open to the public. Five Certified Crop Advisor CEUs (4.5 SW & 0.5 NM) will be available for a nominal fee.  Expo details are at:


Soybean Aphid and Bean Leaf Beetle Management Tour – August 8


Management techniques for the soybean aphid and bean leaf beetle will be highlighted at a tour on the Iowa Learning farm site on the Rob Stout farm south of West Chester on Wednesday, Aug. 8. Since first being discovered in the Midwest in 2000, soybean aphids have tended to be more of a concern in odd numbered years, so this may be more of a pest this year than last. No-till soybean plots that were planted with and without the seed treatment “Cruiser” are the focus of research conducted on this Iowa Learning Farm site. Seed applied insecticides can provide good early season bean leaf beetle control and also provide some control of soybean aphids, especially when planting is delayed as it was this spring. Also discussed at the tour will be value added crop opportunities, including “low lin” soybeans. A rain simulator will also be demonstrated at the site. A free meal, courtesy of QUALISOY ( will be available at 6:30 p.m. followed by the tour. The Iowa Learning Farm project is a unique partnership of agencies, farm and conservation groups, the general public and Iowa State University. Iowa Learning Farm project staff work to increase the adoption of residue management and conservation practices that are expected to improve water quality.



If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: July 5, 2007
Contact: Jim Fawcett

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