Soybean Disease Control: Fighting Fungus

By |

Scouting In Soybeans

With planting season underway throughout the Midwest, finding the most efficient and economical way to go about preventing yield-robbing disease is a trending topic among retailers and growers.

La Niña conditions could have increased the presence of disease pathogens in fields which may lead to a challenging disease control season this summer, although a lot will depend on whether July and August are primarily cooler and rainier than in the past.

“I think this year a lot is going to depend on what July and August shape up to be,” says Nick Fassler, BASF technical marketing manager. “The way we’re going right now, with the opportunity for earlier planting, I think growers have the potential for higher yields, therefore there’s going to be more yield to protect once fall comes around.” 

Naturally then, growers want, and need, to know when and where to scout, how often and what fungicides to apply (or not to apply in some cases) to keep their crop fit until harvest time, and ag retailers are in the best position to guide them.

Yet, while the experts and individual growers may disagree on which management methods are most prudent for their operation, there is one aspect of soybean production that all agree is not likely to vary significantly from grower to grower.   

“Gone are the days where you can just plant the crop, go fishing and come back and harvest it,” says Alison Robert­son, Iowa State University plant pathologist. “If you’re going to maximize yield, you’ve got to baby this crop.”

For many the idea of “babying” anything can seem over­whelming, but enhanced scouting tools and fungicide chemistries — along with knowledgeable retailers taking a greater role in educating growers — are making the task easier to accomplish than ever before.

Increasing Disease Pressure

According to Eric Tedford, fungicide technical brand manager with Syngenta, disease pathogens are developing ahead of schedule this year due primarily to the warmer environmental conditions, increasing the susceptibility of soybeans to disease. Darren Mueller, Iowa State University assistant professor of plant pathology, seconds that notion.

“Most of these diseases are so dependent on conditions during the season and a grower can have all the inoculant in the world, but if it’s 95 degrees out, you’re not going to see a whole lot of frog-eye or white mold,” says Mueller. “So most diseases are very dependent on the weather both before and during the season.”

Also important in establishing a solid yield is the planting date itself, says Fassler. “The earlier growers can get those soybeans in the ground, the longer growth stage they’re going to enjoy throughout the season.”

Still, with the longer growth stage in play, disease is presented with greater opportunity to establish itself in a growers field.

Three soybean diseases in particular — frog-eye leaf spot, Asian soybean rust and brown spot — are expected by many to give unprepared growers their fair share of headaches this summer. Of course, implementing a solid management plan is crucial to overcoming those pests, and Tedford and Syngenta have several recommendations for worried growers.

“Growers need to make good seed selections — deploying genetics that get the job done — and utilize a disease control program featuring the proper fungicides for that field,” says Tedford. “How’s the old saying go? An ounce of prevention is worth a pound of cure.”

According to Tedford, Syngenta is taking the forefront in the battle against soybean disease with both Quilt Xcel and Quadris Top, two newer fungicides that may be foreign to some growers.

Quilt Xcel is a combination of azoxystrobin and propiconazole and is “an excellent player as it has the same spectrum of activity for disease control as Quadris and it also controls your resistant frog-eye,” says Tedford. “You’ll also still be getting the plant performance benefits that we’ve come to expect from azoxystrobin, as well.”

Quadris Top, an azoxystrobin and difenoconazole mix, is also a good option for growers as it provides significant control where QLI resistance is seen, according to the company.

Combining those two technologies with an insecticide, in this case Endigo ZC, is also being tested and the initial results are encouraging.

“That has proven to be a very effective tool in areas where you find both high disease pressure and high insect pressure,” says Tedford. “So far the folks that have tested it are very excited and happy with the combination.”

As for BASF, it continues to recommend growers use Headline, applying the fungicide either by ground or aerially during the R3 growth stage at podset. Priaxor, a new fungicide containing the active ingredient F500 (same as Headline and Stamina), as well as the recently registered chemical Xemium, should provide growers a great late-season option for foliar applications, notes Fessler.

“It’s going to be a great option for growers battling late season foliar diseases, primarily targeting things like Septoria brown spot and frog-eye leaf spot,” says Fessler of Priaxor, which received EPA registration in early May. “We also will typically recommend growers use an adjuvant to improve coverage and increase spreading over the leaves’ surface.”

Sorting through all of these options and deciding which one fits an individual grower is where the retailer enters the picture. 

“Retailers are supporting growers and helping them to make informed decisions more than ever before,” says Tedford. “They have a breadth of knowledge to offer and are a frontline, huge advantage to the growers to help protect their crops so they can reach full yield potential.”

Along those lines, Robertson also reminds growers to make sure that they take advantage of the gauntlet of resources available on the web, citing local University Extension pages and the Plant Health Initiative, a North Central Soybean Research Program (NCSRP) initiative launched back in 1993, as increasingly valuable information sharing tools.

It was via those info-sharing networks that have become so prevalent over the past several years that led Mueller to discover that several counties in Florida have discovered the earliest ever finding of Asian soybean rust.

Fighting The Good Fight

According to Robertson, there are several factors that can increase a seeds vulnerability to disease, among them:

  • Low Quality Seed: Cracked seed coatings can make the seed more attractive to pathogens.
  • No-Till Fields: Cool and wet soil conditions in a no-till field is a breeding ground for disease.
  • Herbicide Use: Some herbicides can actually increase disease susceptibility.
  • History: Fields with a long history of disease will always be at an increased risk.

Therefore, like BASF and Fessler, Mueller and ISU also recommend applying foliar fungicides during the R3 growth stage, although growers should be advised the R3 stage will come sooner this year than in the past due to the weather and earlier planting date. And just as researchers are discovering more and more herbicide-resistant diseases, Mueller cautions growers and retailers alike not to overuse fungicide technologies lest they face the same plight.

“One of the biggest messages retailers need to keep in mind is, with what we’ve seen with herbicide-resistant weeds, that is definitely a possibility with fungicide-resistant pathogens,” said Mueller. “Our encouragement is that people use them as responsibly as possible.”

“For example, frog-eye is one of the more devastating pathogens on soybeans,” continues Mueller. “Re­searchers at the University of Illinois have already found resistant frog-eye in four different states, so it’s a matter of time before some of these common foliar diseases are going to be insensitive to some of these fungicides. Growers need to really take a hard look at ‘Are these fungicides really worth it?’ and figure out where they are needed.”

According to Mueller, the best way for growers to figure out whether or not they actually need the technology is to first embrace weekly field scouting. Then, after analyzing the results, growers should be able to make an informed decision.

“I don’t want to come across as entirely negative because there certainly are fields that need to be sprayed with a fungicide,” says Mueller. “And so our encouragement is to take advantage of the plethora of scouting tools out there. People are running out of excuses not to scout and have that scouting effort drive their decisions.”

Also important is the planting date itself, as it is always prudent to plant seed when conditions are ideal.

“The sun may be shining and you may be itching to get these soybeans in the ground but just wait until the fields have drained a little bit better so you don’t run into agronomic issues that could stress the seedlings during germination,” says Robertson.

“Soybean seed is getting more and more expensive so growers want to plant the bare minimum required to maximize the yield potential on that field,” says Robertson. “So that means cutting down on seed, which makes every seed all that more important and they want to protect that investment.”

Adds Fessler: “The big thing I’ve seen this year in talking to growers and such is that with the current soybean prices, there really is an opportunity to manage the crop to its full potential,” says Fessler. “I think if we can get a good early stand and have good growing conditions late season, that’s historically where we’ve seen the greatest response from fungicide applications for soybeans.”

For updated information on managing soybean diseases and other plant health issues, visit the Plant Health Initiative.

Grassi is the Assistant Editor for the CropLife Media Group, including CropLife and CropLife IRON magazines and the PrecisionAg Special Reports. He joined the staff in February 2012.

Leave a Reply