Using the ‘Disease Triangle’ to Combat Northern Corn Leaf Blight

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For strategies to minimize yield loss due to Northern corn leaf blight (NCLB), Dr. Alison Robertson, an Extension Field Pathologist Professor at Iowa State University, offered insight on how to manage this yield-robbing disease.

The Disease Triangle

Robertson says the foundation tool for scouting for NCLB is the disease triangle, which describes the three factors needed for diseases to develop:

  • Pathogen presence
  • A susceptible host
  • Favorable environmental conditions

Pathogen Presence

While no-till and minimum tillage practices have many benefits, they can also create higher potential for disease development.

“Foliar disease pathogens survive in field residue,” Robertson explains. “Any acres where you have residue could be considered high-risk acres.”

To determine where NCLB might be lurking, keep accurate historical records of disease outbreaks. The next step of the disease triangle is evaluating the susceptibility of the crop.

A Susceptible Host?

In evaluating crop susceptibility to NCLB, consider the two “H Factors” – hybrids, and again, history.

“Look at the hybrid score for corn seed and see if it’s rated as more susceptible for the disease,” recommends Robertson. “Today many growers are farming more acres than ever, so prioritizing at-risk acres is key. We recommend beginning with fields with more susceptible hybrids.”

And history – knowing which hybrids your grower has planted and how they have fared against NCLB – is vital.

Part of helping your growers manage disease is developing a customized disease management plan and making sure growers understand the tools available to prevent and control disease, such as Headline AMP® fungicide. Studies have shown that Headline AMP decreases stress during pollination and grain fill by:

  • Controlling foliar diseases like NCLB
  • Reducing ethylene and oxidative stress, which gives plants greater stress tolerance and sustains productive photosynthesis*

Favorable Environment

The last aspect of the disease triangle is environmental conditions. These are the crucial factors in creating an environment favorable to the development of NCLB:

  • Temperature: NCLB thrives in cooler temperatures (65° to 80°).1
  • Precipitation: Frequent precipitation and overcast conditions are things to watch out for.
  • Topography: Fields near rivers could be subjected to heavier, lengthier dew periods than other areas. “Pay special attention to any areas that will naturally be cooler, such as river bottoms or shadier areas,” recommends Robertson. “Corn leaves need to be wet for an extended period of time for Northern corn leaf blight to really take hold.”

In order to stay a step ahead of NCLB and minimize yield loss, it’s important to be aware of the conditions that favor the development of the disease. If your growers are experiencing any of these environmental conditions, that’s your trigger to make a proactive fungicide application. Products such as Headline AMP® fungicide are powerful tools to control diseases like Northern corn leaf blight. Studies have shown that Headline AMP delivers the most yield at tassel stage (+12 – 15 bu/A)*. You can download the technical bulletin detailing these studies and the results here.

Signs of Northern Corn Leaf Blight

The signs of NCLB are easily recognizable, says Robertson. “You’ll see cigar-shaped lesions, about 2-6" in length – these can appear anywhere on the corn leaves,” she explains. “They’re usually light tan in color, but if you see a lot of dew on the leaves, the lesions can appear gray, meaning they are producing a lot of spores.”  


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