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Angie Peltier


Angie Peltier
Former Extension Educator, Commercial Agriculture



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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Image: Howard F. Schwartz, Colorado State University, Bugwood.org

Foliar fungicides: Factors to consider


Although corn seeds have not yet been sown, many producers are already scheduling foliar fungicide applications. Recent University of Illinois research results can help producers increase the probability of making a profitable foliar fungicide application.

Dr. Carl Bradley, U of I Field Crops Plant Pathology Extension Specialist, and his team, have conducted a total of 33 foliar fungicide experiments between 2008 and 2012 at several locations throughout Illinois. They investigated the effects of foliar fungicides on corn foliar and stalk disease severity and grain yield.

Increasing the probability of a 'profitable' application. Dr. Bradley's team found that the probability of achieving a 'profitable' foliar fungicide application, or a fungicide application in which the yield response to the fungicide (compared to the untreated control) at least paid for the cost of the application, is dependent upon application costs, commodity prices, and foliar disease severity.

We saw that in 2012, high commodity prices led more people to practice 'insurance pest management' rather than 'integrated pest management'. However, whether corn prices are $4 or $8, scouting just prior to tasselling and making fungicide decisions based upon disease incidence and severity continues to increase the probability of achieving a profitable fungicide application. Under low disease pressure environments, the average yield response to a foliar fungicide applied between VT (tasselling) and R1 (silking) was 3 bushels per acre and there was a less than 45 percent probability of achieving 3, 5 or 8 bushels per acre. While under moderate to high disease pressure environments, the average yield response was 10.2 bushels per acre and there was a more than 60 percent probability of achieving 3, 5 or 8 bushels per acre.

Fungicide timing is also very important. Research has shown that fungicide applications during the mid-vegetative growth stages (V5-V6) do not significantly reduce foliar disease severity or increase yields when compared with either untreated controls, or applications made at VT or R1.

Some foliar fungicides have been marketed as being able to decrease stalk rots or improve 'standability'. When corn leaves aren't able to complete enough photosynthesis to provide enough sugars to feed the demand of the growing kernels, the plant starts to rob sugars from roots and stalks, thereby weakening the plant. This reallocation of nutrients tends to occur in hybrids that are susceptible to foliar disease under moderate to severe foliar disease pressure. Dr. Bradley's group has found that reducing stalk rot severity through the application of foliar fungicides is largely the result of reducing foliar disease severity. Significant reductions in stalk rot severity tend to occur most often when hybrids susceptible to foliar disease are under moderate to severe disease pressure. Much of Dr. Bradley's fungicide trial data is summarized in the University of Illinois Corn & Soybean Classics Proceedings.

Spray droplet-size – an important consideration for tank mixes. Many crop protection chemicals have begun specifying spray droplet size to comply with EPA guidelines. For example, a systemic foliar herbicide may require very course droplets, while a contact fungicide may require fine droplets. Spray nozzle orifice size and application speed and pressure help those that apply these chemicals create a balance between maximizing coverage of the target organism and minimizing off-target application. It may be beneficial to pay close attention to droplet size specifications on chemical labels as different products in a desired tank mix may require vastly different droplet sizes for label compliance and efficacy. Drs. Robert E. Wolf and Scott Bretthauer have put together a nice resource entitled, "Droplet Size Calibration: A New Approach to Effective Spraying".

Fungicide stewardship – ensuring the longevity of our tools. Natural selection is the process by which selection pressures can shift the genetics of population through generations. A selection pressure is exerted on the pathogen population every time a fungicide is applied. Those members of the fungal population that are sensitive to a fungicide do not survive to reproduce, while those that are able to withstand the fungicide application can survive to produce offspring.

To ensure the long-term utility of our chemical tools, there are several practices that can be employed to reduce or delay the selection of fungicide-resistant pathogen populations:

  • Use crop scouting to make IPM-based, full-rate fungicide applications.
  • Rotate fungicides or use tank mixes of fungicides with different modes of action.


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