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Corn+Soybean Digest

Data Discrepancy

In foliar fungicide trials, why is there sometimes a discrepancy between the soybean yields that company researchers observe and the ones that university researchers see?

Plot size is one factor involved. Industry generally uses large plots (20 or 40 acres, for example), while universities generally use smaller test plots. The variability in yields in small plots does not accurately reflect what occurs in a grower's field, says Bond McInnes, fungicide development manager, DuPont Crop Protection, adding that DuPont uses large plots (generally 40+ acres) for yield evaluations.

Shawn Conley, Extension soybean and small grains specialist, University of Wisconsin-Madison, (UW) says that university research focuses on replicated (three replications minimum at UW) field trials, while industry generates more split field data. Replicated trials allow researchers to find true or real differences instead of saying this half of the field yields more than the other, Conley says. Fields that are split in half could have historical differences between the sides of the field. Growers are more likely to try a product on the good side of the field vs. the bad side, Conley says.

University research also will take into account the margin of error, while industry looks more for trends happening in the field (60-70% of the time, something will happen, for example), Conley says. Before he would recommend a particular practice, such as applying fungicides for plant health/yield response, a real difference would need to happen 90% of the time, he adds.

IT ALSO IS difficult for universities to plant large plots with the number of treatments they study. Promising treatments can be tested in larger plots later, Conley says. “I think the biggest issues for growers to consider are the lack of true replication within split field plots and poor calibration of yield monitors,” Conley adds.

University research plots are planned way ahead of time, and are often conducted regardless of environmental conditions, says Randy Myers, product manager, Bayer CropScience. Harsh conditions may diminish the impact of a fungicide spray. When data from several universities across a region are pooled, the results from favorable trials may be diluted in the average, Myers says.

“Growers need concrete, conclusive data. When we do trials, we try to consider limiting factors. For example, if it's really dry, you cannot spray a fungicide and expect it to completely make up for a lack of water or overcome a nutrient deficiency. If there are other, more limiting factors, it becomes difficult to measure yield impact from a particular variable, such as a fungicide application,” Myers says.

When evaluating yields, growers should ask how the trials were set up, says Tim Maloney, president, Agri-Tech Consulting, an independent agronomic testing firm in Janesville, WI. They should ask about plot size as well as variety planted, previous cropping and tillage systems, row spacing and seeding rate. Yield differences can come from all of these factors, Maloney says. “You also have to consider whether the harvest was taken from the middle of the plot to avoid border effects.”

Boyd Padgett, professor, Macon Ridge Research Station, Louisiana State University Ag Center, says that yield differences also could be due to environmental conditions, variety and whether test sites rely on native inoculum or introduced inoculum.

PALLE PEDERSEN, Extension soybean agronomist, Iowa State University, has conducted tests in traditional small plots (10×25 ft.), but also in larger plots and has not seen any significant yield differences among them. He does not do any research without statistics and “numeric” values do not mean anything to him, he says.

“I want to assure growers that the observed differences are more likely to have been caused by the treatment applied and not by something else,” says Pedersen.

He has tested fungicides since 2004 on different soybean varieties and at different application times. The upper Midwest does not generally have enough foliar disease to justify the expense of fungicides, Pedersen says, adding that 80% of the yield loss in upper Midwestern soybeans comes from soil-borne diseases. The upper Midwest generally does not receive enough moisture in July and August to cause an epidemic and significant yield loss from foliar pathogens.

In the South, with high humidity, late-season moisture and mild winters, fungicides have been used for years. Here, application timing can be an important factor in yield response.

The majority of the research work in Mississippi and other states has been done at the R3-R4 stage of soybean growth. Fungicide application at those stages has proven to be a beneficial application timing when soybeans have followed soybeans, says Tom Allen, Extension plant pathologist, Mississippi State University's (MSU) Delta Research and Extension Center.

“Typically, we recommend applying fungicide at the R3 growth stage,” says Eric Tedford, Syngenta Crop Protection. Most foliar diseases do not appear until then, and by applying fungicide at R3, the grower is protecting the soybean into the R4 through R6 stage, critical times for yield determination, Tedford says.

A surprising number of growers and crop scouts, however, cannot correctly identify the R2 or R3 stage, so they may apply really early or very late, UW's Conley says.

MSU has tested the impact of row spacing. However, most of the testing has been done on 38-in. rows, the most easily adapted row spacing for Southern producers who have switched from growing cotton to soybeans. This has reduced the need for new planting equipment, Allen explains.

Farther north, row spacing is generally narrower. Wisconsin's Maloney prefers 15-in. rows over 30- or 7.5-in. rows. There is less wheel track damage than in 7.5-in. rows, but better row closure than 30-in. rows. “You still get the advantages of better weed control than that of wider rows, but lower seed cost per acre than the 7.5-in. rows,” he says.

Finally, variety also can make a big difference in yield results. “I prefer varieties with both offensive traits for high yield potential and defensive traits with good disease resistance,” Maloney says. He adds that growers should use a good fungicide/insecticide/inoculant seed treatment to start off strong.

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