Breaking Down the Disease Triangle

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All crop disease results from the interaction of three main factors that make up the disease triangle: a pathogen, the right environment and a susceptible host in the same field. And whether it’s tar spot on corn or white mold in soybeans, the best way to limit yield loss to crop disease is to keep it from developing in the first place.

“Once you lose leaf area to a disease, you’re not getting it back,” says Jason Gibson, market development specialist, Corteva Agriscience. “So, understanding the interaction of pathogens, the environment and your host plant is important, because knowing when disease is likely to occur will help you better time fungicide applications.”

Let’s break down each aspect of the disease triangle in crop production:

  1. The pathogen. A pathogen is a disease-causing microorganism, such as a bacterium, fungus or a nematode. Depending on the disease, some management practices such as crop rotation or tillage can reduce the number of pathogens present in a field.

    “Tillage can help with burying pathogens in the soil and making them less likely to impact the crop in future years,” Gibson says. But tillage would not be effective for preventing diseases such as common rust, because the fungus spores are wind-borne and do not overwinter in the United States.
  2. The environment. “Paying attention to the weather will help you better predict the likelihood of disease development,” Gibson says. While the favorable environment for development can vary by disease, many crop diseases are favored by persistently moist, cool conditions with temperatures in the 60s and 70s. 

    “If you’re experiencing a period of hot and dry weather, it’s less critical for you to be out scouting for disease,” Gibson says. “But if you get the right set of environmental conditions persisting, diseases such as tar spot or gray leaf spot can take off very quickly. We’ve seen this in 2023.  Several areas of the Corn Belt started the season with drought conditions and, after some moisture moved in, crop disease caught many farmers by surprise.”
  3. The plant host. “The host is the factor that you typically have the most control over,” Gibson says. “When you know the disease pressure you’ve dealt with in prior seasons, you can purchase hybrids or varieties that are less susceptible to that particular disease — provided they bring the yield and other agronomic factors you’re looking for.”

Because preventive action is generally recommended over curative action, be sure to take all aspects of the disease triangle into consideration when deciding on fungicide application timing. You can learn more about specific disease management best practices in our Corn & Soybean Disease ID Guide


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