The Use of fungicide on corn across the Corn Belt nearly doubled in 2007 as farmers adopted what for many was a new practice to protect the yield of the season's higher-value crop. If the trend continues, 2008 will be another banner year for corn fungicides.

But even as the practice becomes more common, university experts question the application of fungicides without regard to the presence of disease, which is recommended by some manufacturers.

Different data

Depending on whose figures you look at, corn fungicide use in 2007 either was a huge success or a break-even proposition at best.

Data compiled from university trials in 12 Corn Belt states and provinces in 2007 showed an average yield response of 3 bu./acre to applications of the three dominant corn fungicides: Headline (from BASF), Quilt (from Syngenta), and Stratego (from Bayer). That's about half the yield necessary to pay for the fungicides, including application costs.

“The majority of our data showed that it would not have paid to spray,” says Carl Bradley, a plant disease expert at the University of Illinois. Fungicide treatments paid off 38% of the time at $3.50 corn and a $20 application and product cost.

However, BASF reports an average yield increase of 12 to 16 bu./acre in 1,150 on-farm trials in 2007. That represents an extra profit of $34 to $51/acre based on corn at $4.33/bu., according to BASF.

“Growers are doing the math and they're finding, on average, a return on investment using Headline fungicide that's upwards of 200% on corn,” says Gary Fellows, a BASF technical manager.

Bayer CropScience reports an average yield increase of about 10 bu./acre over hundreds of on-farm trials.

“It's not just yield; it is harvestability,” says Randy Myers, fungicide product manager for Bayer. “As you move farther north, the yield impact is reduced.”

That north-to-south yield trend was noted in a review of company and university studies reported by Pioneer on its Growing Point Web site (www.pioneer.com/growingpoint; search for corn fungicides). It showed an average advantage to fungicides of 5.9 bu./acre in the western Corn Belt, 8.7 bu./acre in the eastern Corn Belt, and 12 to 13 bu./acre in southern states.

To scout or not to scout

University experts don't question the value of applying fungicides when diseases are present at levels that are likely to affect yield. For example, the most prominent Corn Belt corn disease — gray leaf spot — can have a serious impact on yield when left untreated. But they are opposed to applying fungicides without the presence of disease. Bradley says that their 2007 trials tested the idea that disease doesn't need to be present for a fungicide to pay off and that the relatively low yield response supports a scout-and-treat approach.

Meanwhile, BASF recommends applying its fungicides without scouting to see if disease is present.

Bayer CropScience and Syngenta support scouting first. But scouting often is not practical, says Myers from Bayer CropScience. “We have seen that if you have normal to above-normal rainfall, you will have disease,” he says. “The same conditions that are good for the crop are good for disease. It is very difficult to scout fields.”

However, Syngenta technical manager Eric Tedford says the company recommends scouting first before applying its corn fungicide, Quilt. “The key to fungicide use is to actually scout for disease,” he says. “Based on disease pressure, go in and apply at the R1 plant stage.” (Consult each fungicide's label for application recommendations.)

He recommends following a 2-2-1 scouting procedure: Check two leaves just below the ear on every other plant. If you have one gray leaf spot lesion on the two leaves and environmental conditions are favorable for disease development, treatment is justified.

Better plant health?

All three companies say their fungicides can improve the health of corn plants — and improve yields — even if disease isn't present. Notably, BASF and Syngenta have trademarked terms to describe this capability. BASF's term is Plant Health; Syngenta's is Plant Performance. Bayer calls this capability XLERATE technology, though the term isn't trademarked.

The companies tie this general beneficial effect to the strobilurin chemistry that's in all three fungicides. (Stratego and Quilt also contain an additional fungicide in the triazole family.)

“The strobilurin component enhances carbon dioxide assimilation,” Tedford explains. This, in turn, improves photosynthesis. Transpiration also decreases, which boosts water use efficiency. In addition, ethylene production is inhibited. This allows plants to retain green leaf area longer by slowing down the senescence or aging process.

Myers, from Bayer, says that positive physiological responses from strobilurins also have been noted in wheat, rice and other crops. Scientists are trying to determine the mechanisms responsible for the plant responses.

“My opinion is that it is a real effect,” adds Gary Munkvold, a plant pathologist at Iowa State University. “I don't have a good feel for the size of the yield effect. I am skeptical that it is big enough to pay for a fungicide application.”

2007 revisited

Fungicide use on corn went from being a rarity in 2006 to covering a third or more acres in some parts of the Corn Belt in 2007. Although industry-wide statistics for treated acres aren't available, EZ Trak, a service that reports agricultural retailer sales information, says that corn fungicide sales climbed 84% from 2006 to 2007.

University plant disease experts estimate that fungicides were used on an estimated 10 million to 14 million acres across the Corn Belt in 2007. That's approaching 20% of total corn acres in the region. Farmers in Illinois (three million to four million treated acres) and Iowa (about three million acres) led the way.

“This is a phenomenon that has occurred over about two years,” Munkvold says.

Best bets for 2008

Whether you decide to scout for disease or not before applying a fungicide, university and company experts say some fields, like those described below, are more likely to benefit from a fungicide application than others.

Susceptible hybrids

Hybrids with fair to poor resistance are more likely to benefit from fungicide protection than those with good resistance. In multi-state university trials in 2007, hybrids with fair to poor resistance showed an average 6-bu./acre response to fungicides, even without evidence of disease. Just over half of trials had yield increases of 6 bu. or more. Pioneer reported that moderately resistant and susceptible hybrids treated with fungicides showed average yield advantages of from 10.8 to 18.6 bu./acre. That compared to an average 3-bu./acre response for disease-resistant hybrids.

Corn on corn

Corn diseases survive on the previous crop's residue, so the potential for disease is greater. Yield results from on-farm trials reported by Pioneer showed that applying fungicides on corn-on-corn acres had a 12.1-bu./acre average yield advantage, compared to a 1.5-bu./acre advantage for corn after soybeans.

High-humidity areas

Fields planted in high-humidity areas, such as river bottoms, are more susceptible to disease. The same goes for irrigated fields, Bradley says.

Later-planted fields

More disease spores from earlier-planted fields may be circulating when fields planted later in the season are most susceptible to disease.

Diseased fields

Fields with significant foliar disease pressure had more than four times the yield response as fields without disease, the Pioneer field trial summary showed. Fields with significant disease pressure had an average yield increase of 15.3 bu./acre. Fields without disease produced an average of 3.5 bu./acre more yield when treated with a fungicide.