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:
There must be a susceptible host.
The disease pathogen must be present.
The weather must be conducive for the pathogen to successfully infect the host.
Therefore, ask yourself the following questions:
Does the hybrid have a poor or mediocre foliar disease resistance package?
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
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, http://www.ipm.uiuc.edu/bulletin/article.php?id=793.
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 http://www.ipm.iastate.edu/ipm/icm/2007/6-25/fungicides.html.
The second article should be in the July 2, 2007 Integrated Crop Management
Newsletter and posted at http://www.ipm.iastate.edu/ipm/icm/
FOR YOUR CALENDAR
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: http://wrc.umn.edu/outreach/striptillageexpo/midwest/index.html
Soybean Aphid and Bean Leaf Beetle Management Tour –
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 (http://www.qualisoy.com/)
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