By Robertson, Abendroth, and Elmore
13 Dec 2007 -
An estimated three million acres of corn in Iowa were sprayed mid-season with fungicides (strobilurin or a strobilurin/triazole combination) in 2007. Reasons for spraying included the high price of corn, potential to control diseases and a possibility of improved yield from “plant health” benefits. Until this year, fungicide applications to production cornfields were rarely practiced in Iowa because they were not profitable. In addition, many of the hybrids grown today have good overall tolerance to foliar (leaf) diseases.
Three Iowa State University (ISU) Extension specialists, Roger Elmore, Alison Robertson and Lori Abendroth, developed a research program to examine whether using mid-season fungicides on corn would increase yield enough to increase profits.
“Producers are looking to maximize corn yields today more than previous years because of higher grain prices,” said Elmore, ISU Extension corn specialist. “Some of the management practices that were not economical at one time may now be, considering the new prices. Fungicide application to field corn is one of those management tactics that needs to be reexamined given the new economics and the increased interest in these products. We wanted to evaluate the yield responsiveness associated with an application of a mid-season foliar fungicide on farmer fields across the state.”
In the 2007 growing season, ISU Extension personnel and Corn and Soybean Initiative partners worked together to collect data to:
- evaluate the control of gray leaf spot (GLS), common rust, and stalk rot from a mid-season foliar fungicide application;
- assess the grain yield response of corn to foliar fungicide application;
- determine if foliar fungicide applications are profitable; and
- identify agronomic characteristics (such as hybrid and previous crop) that are important in determining when to spray fields.
“Foliar fungicide applications significantly reduced both common rust and gray leaf spot severity,” said Robertson, ISU Extension field crop pathologist. “In addition, stalk rot severity also was lower in the sprayed treatments. However, the mean yield response to the foliar fungicide application was below a break even yield response of six bushels per acre. This break even (six bushels per acre) was calculated based on the cost of a fungicide application which ranged from $18 to $24 across the state, and a corn price of $3.75 per bushel.”
Research summarized over 26 of the total 35 locations has identified an average yield increase of 3.3 bushels per acre when a fungicide was applied at tasseling (VT) or silking (R1) compared to an untreated control in Iowa. Yet 3.3 bushels per acre is below the yield necessary to cover fungicide and application costs. Only 27 percent of the time was a fungicide application profitable. Fungicides decreased foliar disease severity and stalk rot severity but did not always result in a positive or profitable yield response. Read the complete research report at: the IPM site here or on the crops extension site.
The 2008 growing season is several months away, but already decisions are being made regarding the purchase of fungicides. However, a decision to apply a fungicide mid-season to hybrid corn should be based on IPM management practices as it is simply a management tool that is useful only in conditions where disease pressure would be expected to significantly reduce yield potential.
“We need to remember that any management tool is only going to protect yield when there are factors that would reduce a field’s potential yield, said Lori Abendroth, ISU Extension agronomist. In this case, if there is significant disease pressure then a fungicide application at tasseling or silking could potentially protect yield during the grain fill period. Yet if disease pressure is light, as was seen across most of Iowa in 2007, we would not expect an economical yield increase simply because the crop is not experiencing significant stress and can therefore proceed through grain fill without a problem.”
Consider the following factors before spraying a fungicide in 2008: hybrid susceptibility, disease pressure at tasseling (VT), weather conditions at VT and during grain fill, previous crop and the amount of crop residue present in the field. In general, a fungicide application is not recommended on resistant or moderately resistant hybrids. On susceptible, moderately susceptible or intermediate hybrids, the decision to apply a fungicide is based on the level of disease pressure at the time near application.