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Serving: IA

Spraying Foliar Fungicide Can Aid Corn Health

Spraying Foliar Fungicide Can Aid Corn Health
Applying foliar fungicides to corn and soybeans can pay when weather favors fungal disease development.

Although some growers across Iowa were able to begin planting corn in a timely manner this spring, many waited for more optimal conditions and with good reason. February and March consistently brought below-normal temperatures and April temperatures varied greatly. These conditions created a stressful environment for newly planted corn, and depending on which week you planted, the obstacles you face this growing season will vary.

DEFEND AGAINST DISEASE: When does it pay to spray a fungicide on corn and soybeans? When disease is present foliar fungicides are an effective management tool, but weather and other factors play a big role in yield response.

On the extreme end, threats from especially cold soil temperatures included imbibitional chilling injury, which can lead to stunting of the root system and delayed or complete failure of emergence. Another risk from planting into cold, wet soils is development of seed rots and seedling blights. Poorly drained soils create an environment that fosters diseases, such as Pythium, Fusarium, Diplodia, Rhizoctonia and Penicillium which can lead to rotting of seedling roots, yellowing and wilting.

 Applying a foliar fungicide can help corn withstand stress
"Because of the unusually cold, wet spring this year seed rots and seedling blights were more prevalent for some growers," says Eric Tedford, fungicide technical product lead for Syngenta. "While foliar fungicides cannot treat seed rots in corn, applying a fungicide later on in the growing season to provide plant stress management benefits, such as Quilt Xcel fungicide, can encourage development of a stronger root system, even in an environment with cold stress. This helps corn withstand stresses that may appear later in the season."

Farmers who avoided these worst-case scenarios after planting around rainy, near-freezing conditions may still be at risk of their corn developing a shallow root system. Tedford says, "Cold, wet conditions can lead to stressed, underdeveloped roots, which increase a crop's risk for nutrient deficiency and disease pressure, and also affects standability."


While variable soil temperatures are unlikely to cause corn injury, it can lead to inconsistent germination and inconsistent emergence. For example, in 2006, a large temperature variation occurred across Iowa at planting time, resulting in erratic and uneven stands with crop development varying up to two growth stages.

Effect of fungicide application on corn with uneven tasseling
Rich Lee, a Syngenta agronomist in eastern Iowa says in years with uneven emergence, foliar fungicide application can become more complicated. "Many fungicides must be applied with an adjuvant, which restricts application timing options and can affect crop safety," he notes. "A fungicide, such as Quilt Xcel, that can be applied with water gives you peace of mind that you won't interfere with pollination on a year of uneven tasseling.

 "Weather stress seems imminent in Iowa," adds Lee. "The past few years we've experienced everything from floods to drought. We can't control the weather, but we can manage some of the potential stress it can cause. Instead of waiting to see how the weather plays out, growers should anticipate conditions to be less-than-ideal and apply a fungicide that offers stress management benefits."

These stress management benefits can pay off throughout the season, he says. As temperatures continue to rise, the foliar fungicide improves corn's water use efficiency so plants can better tolerate periods of hot, dry weather. Fungicide applications also lead to stronger stalks that result in less lodging for a more efficient harvest, he says.

Syngenta economic models indicate corn treated with Quilt Xcel can be harvested 1.7 mph faster than untreated corn, which saves an average of $10 per acre in fuel and equipment costs, says Tedford.


With high temperatures and thunderstorms during the growing season, you must be mindful of foliar diseases that thrive in warm, wet conditions, such as gray leaf spot, rust or northern corn leaf blight. A fungicide may be applied early (V4 to V8 corn growth stages) or around the R1 growth stage of corn, to combat these diseases.

Stewardship of fungicide use is still important
The potential yield-boosting power of foliar fungicides has become evident to farmers as fungicide application has become more common. Though these tools have become commonly used in the past five years, they must be used wisely, says Iowa State University Extension plant pathologist Alison Robertson. Unwarranted fungicide applications can lead to increased risk of fungicide resistance, she says.

Carl Bradley, Extension plant pathologist at University of Illinois agrees and is cautious about making applications that aren't really needed if there is no disease present. "Fungal plant pathogens can become resistant to fungicides, similar to weeds becoming resistant to commonly-used herbicides."

Bradley was a speaker at the Iowa On-Farm Network Conference last winter in Ames. He points to research from a Tennessee soybean field that confirmed Cescospora sojina, the fungus that causes frogeye leaf spot, to be resistant to strobilurin fungicides. Bradley says more research is underway, "but we now ask, what challenge is next?"

Moving deeper into the growing season, you should continue to be mindful of how planting and weather conditions could affect your crop this year. "No two years are the same, and it's important for growers to select the right tools that bring value regardless of growing conditions," says Tedford. For more information on foliar fungicide application and use, visit

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