Source: News from Syngenta

Since arriving in the United States in late 2004, soybean rust has dominated agricultural news.  There is no shortage of information available to growers on the topic, as Web sites and meetings have popped up everywhere specifically to address the potential impact of rust.  This information is necessary, as rust potentially poses a severe threat to soybean production, but experts warn growers not to let rust overshadow other late-season diseases that lower yields every year.

In any given year, Southern growers who choose not to make a soybean fungicide application can expect some degree of yield loss, according to Alan Blaine, Mississippi State University extension soybean specialist.

“Foliar diseases are something that we have to deal with every year.  They’re quite widespread,” said Blaine, citing anthracnose, pod stem blight, frogeye leafspot and late-season Cercospora as some of the more common diseases that thrive in hot, humid Southern weather.

“Our growers in the deep South are applying a whole new level of management to the crop that we didn’t do wide scale 15 years ago.  A part of that management is attempting to control foliar diseases,” he said.  These management practices include earlier planting, the use of earlier maturing varieties and timely applications of a foliar fungicide.

Before applying a fungicide application, Blaine encourages growers to consider their yield potential.  In irrigated fields or high management situations, a fungicide application may give fields a boost to achieve higher yields.  Fungicide applications may not offer substantial returns in drought situations or on some early planted fields.  If a grower decides to spray for foliar diseases, Blaine encourages him to make the application between R3 and R4. 

In numerous trials, Blaine and others have found the application of a strobilurin fungicide application to pay off.  “Since the late 1990s, we’ve been averaging a 5.9 bushel yield increase with a strobilurin-based program.  That increase is the average of over 130 on-farm trials and side-by-side comparisons,” he said.  Blaine’s findings are not unique to the South.  In more than 570 in-field Syngenta trials across the United States, Quadris® fungicide, a strobilurin, boosted yields an average of 5 to 6 bu/A.

In 2005, Dr. Wayne Pedersen, soybean plant pathologist at the University of Illinois at Urbana-Champaign, noted 100 percent incidence of anthracnose stem blight in some fields following late-season rains.  Through a series of trials funded by the Illinois Soybean Check-off Board and agrichemical companies, including Syngenta Crop Protection, Pedersen concluded that foliar diseases can impact yields, but timely applications of strobilurin fungicides applied around R3-R4 can control those diseases and prevent yield losses.

Pedersen evaluated four to eight soybean varieties and 16 fungicide treatment combinations at eight locations, ranging from Metropolis in the far south to Dekalb, near the Wisconsin border.  Only two locations did not have a significant yield increase, and they were very dry during pod fill.  Across the varieties, the boost in yields was approximately 4.8-7.5 bu/A. 

“What we’re seeing, without a doubt, is exactly what the Brazilian farmers have seen as well.  There is yield loss due to lack of late-season disease control,” Pedersen said.  “The exciting part from my side of it is that I think we’re capturing a fair amount of yield we didn’t know we were losing.  When you see a 12-bushel yield increase on a grower’s field, he gets excited and says, ‘You mean every year I’ve been losing this?’  My answer to that is, ‘I don’t know about every year, but the potential loss from late-season diseases is far greater than we ever thought.’”

However, the threat of soybean rust has caused some growers to deviate from this tried and true fungicide program.  In 2005, many Southern growers postponed their fungicide application in hopes of treating foliar diseases and rust at the same time.  Instead, rust never materialized, and they missed the window for a profitable foliar application. 

Blaine understands growers’ fears.  However, he thinks the economic benefits of an average 5.9 bu/A increase outweigh the negatives of an additional application, and he encourages growers to make the decision to spray for foliar diseases independently of rust.  “I think we need to go ahead and make that shot when warranted whether we have rust or not, even if rust puts us in a 2-shot program from time to time.  Rust doesn’t overly concern me.  I’ve seen it, and I know we have material that will control it,” Blaine said.  “I’m telling growers, ‘We have already got your rust program paid for just spraying for other diseases.’  The return is much greater than what a fungicide program for rust will cost you.” 

If rust poses a threat, Blaine says growers may need to make modifications to their program.  A combination application, such as Quilt®, that combines preventive and curative activity in one product might be a better choice.  Quilt contains azoxystrobin, the active ingredient in Quadris, offering growers late-season disease control benefits as well.  A new option in 2006 is tank mixing Alto®, a crop-safe triazole, with Quadris, providing preventive and curative activity in one application.  Alto contains cyproconazole, which proved itself as a leading soybean rust treatment Brazil and recently received an EPA Section 18 for control of Asian rust on soybeans in the United States. 

However, the basic premise of Blaine’s recommendation will remain the same.  “Right now, my fungicide program is a strobilurin at the R3-R4 time frame,” Blaine said.  “Rust or no rust, I’m going to have a strobilurin in my fungicide program.  Fungicide will make growers money, year in and year out, on every acre they grow beans on if they plant timely.”

Requests on behalf of several states have been submitted to include Alto on EPA’s approved Section 18 list for control of Asian rust on soybeans. The following states have requested an Alto Section 18 Quarantine Exemption from EPA: AL, CO, DE, IA, IL, IN, KS, KY, MD, MN, MO, MS, NC, NE, NJ, OK, SC, SD and TX. As of this printing, EPA has granted section 18 approval for use on soybean rust in Illinois, Iowa, Maryland, Minnesota, Missouri, Nebraska and South Dakota. Check with your state prior to using or recommending Alto for control of Asian rust on soybeans.

As of this printing, Quilt received approval for use on Asian soybean rust under a Section 18 Quarantine Exemption in the following states:  AL, AR, CO, DE, FL, GA, IL, IN, IA, KS, KY, LA, MD, MI, MN, MS, MO, NE, NJ, NY, NC, ND, OH, OK, PA, SC, SD, TN, TX, VA, WV and WI. If your state is not listed, check with your state prior to using or recommending Quilt for this use.

Quadris®, Quilt® and Alto® are trademarks of a Syngenta Group Company.