DuPont Crop Protection [1]

Disease-Control Strategies to Help Avoid Fungicide Resistance

The quest for healthier crops and higher yields triggered a decade of increased fungicide use. Grower interest in fungicides soared after Asian soybean rust was identified in the United States in 2004. As agronomists responded with advice on scouting and fungicide use, the potentially devastating crop threat became manageable.

After the initial Asian soybean rust scare cooled, soybean growers began reporting yield improvements from fungicide use, even under low to moderate disease pressure. University and company trials confirmed those observations. For example, in 148 on-farm trials conducted by DuPont Pioneer from 2007 to 2011, fungicide applications alone or applied with insecticides increased soybean yield by 2.9 to 5.5 bushels per acre on average. Today’s higher grain prices make yield gains of that magnitude an economically viable reason to apply fungicide between the R2 and R5 growth stage to control common fungal diseases.


Over time, some plant diseases have developed fungicide resistance. “Growers are now learning to not rely on just one fungicide mode of action, and fungicide choices have improved,” said Todd Robran, grains fungicides and insecticides portfolio manager, DuPont Crop Protection. “DuPont has been working hard to bring growers the tools needed for evolving resistant disease populations.”

One example is a new fungicide that combines two modes of action for effective disease control and to help manage resistance. DuPont Aproach® Prima fungicide uses the same unique strobilurin found in DuPont Aproach® fungicide for preventive and curative control, plus a triazole to help control diseases such as frogeye leaf spot (including strobilurin-resistant populations), anthracnose, septoria brown spot, cercospora leaf blight, pod and stem blight, and soybean rust. Systemic movement within the plant protects all plant surfaces, including those near the soil where diseases often start, plus stems and leaves that have not emerged.

Robran points to field trials throughout the country where Aproach® Prima reduced incidence of disease and increased yield.

  • In soybeans, applying Aproach® Prima decreased severity of resistant frogeye leaf spot by more than 67 percent and increased yield by 6 bushels per acre over soybeans not treated with fungicide.*
  • Aproach® Prima applications decreased soybean rust incidence by 92 percent compared with untreated control plots, while Quilt Xcel only reduced rust incidence by 42 percent. That improved disease control increased soybean yield by 16 bushels per acre over Quilt Xcel plots.**


Overuse of any fungicide increases risk of developing disease resistance. Many fungi are polycyclic, producing spores in multiple cycles during the growing season. Each reproductive cycle presents another opportunity for resistant spores to replicate. Some diseases pose a greater risk for resistance development, including rusts, powdery mildews, leaf spots and blights. Heather Marie Kelly, extension plant pathologist, University of Tennessee, notes that frogeye leaf spot [4], in particular, can quickly develop strobilurin resistance.

“Strobilurin fungicides are still very effective tools for managing soybean diseases,” Kelly says. “However, as with any resistance management program, it’s important to use multiple modes of action to control disease. With two modes of action, Aproach® Prima fungicide provides good disease control for frogeye leaf spot and other diseases. It’s a good tool for resistance management.”

DuPont Crop Protection is collaborating through the Fungicide Resistance Action Committee [5] (FRAC) to monitor plant disease and identify best practices to reduce development of fungicide-resistant diseases. A University of Kentucky plant pathology fact sheet, Principles of Fungicide Resistance [6], provides more details about how diseases develop resistance to fungicides. Ask your DuPont Crop Protection specialist about how an integrated foliar health program that includes Aproach® Prima fungicide and appropriate insect control can improve yield potential and reduce the risk of resistance in your fields.

* Results from a 2011 trial conducted by M. Newman, Tennessee.

** Results from a 2012 Auburn University trial including Aproach® Prima and Quilt Xcel fungicide. Applications made at R2 and 14 days later.

Always read and follow all label directions and precautions for use.

Quilt Xcel is a trademark of a Syngenta Group Company.

DuPont Aproach® Prima may not be available in every state. See your local DuPont representative or retailer for details on availability.

The DuPont Oval Logo, DuPont™, The miracles of science and Aproach® are trademarks or registered trademarks of DuPont or its affiliates.

Copyright © 2014 E. I. du Pont de Nemours and Company. All rights reserved.