Fungicides 2018: Looking at New Pressures, Including Resistance

Historically, fungal diseases have tended to take something of a backseat to their higher profile brethren in the pest and weed worlds. In fact, as many fungicide company representatives have observed over the years: “Fungicides are generally one of the last inputs that go into the production of corn and soybeans.”

In recent years, due in large part to lower commodity prices, this trend has been differently in evidence. For many years during the ag economic boom times of 2009-13, many growers were liberally applying fungicides to their crop fields as a preventive measure — even without any disease pressure. But this has now waned, apparently. In fact, according to data compiled during the 2017 CropLife 100 survey of the nation’s top ag retailers, 40% of respondents said their grower-customers had decreased spending during the year on this practice. Only 28% reported an increase in this area, with the remaining 32% seeing no change in fungicide application practices between 2016 and 2017.

Despite this fact, overall fungicide sales remained strong during 2017. According to the 2017 CropLife 100 survey, almost half of the nation’s top ag retailers ­— 48%, to be exact — reported sales increases between 1% and more than 5% for the year. Only 29% indicated these sales were down by the same amounts.

According to Troy Bettner, Market­ing and Business Development Leader for HELM Agro US, the reason that fungicides seem to be gaining popularity ties back to professional work that proves their worth. “Awareness of plant disease and its impact on yield is still at a high level in the grower community,” says Bettner. “As a result of university and Extension education programs, the benefits of fungicide use are becoming better understood.”

Looking Back, Looking Ahead

During 2017, says Bettner, a large portion of the U.S. was rainfall deficit, with many areas of the country suffering from drought conditions. Naturally, this impacted disease development across much of the corn and soybean growing regions of the nation, particularly in the Midwest.

“On corn acres, common and Southern rust was commonly seen in locations, while gray leaf spot and Northern corn leaf blight made an appearance in other areas,” he says. “Late season common ear rot diseases were also found in pocket areas.

“In soybeans,” he continues, “frogeye leaf spot, target spot, septoria leaf spot, cercospora leaf spot, and Asian soybean rust were problematic for growers in certain geographies.”

Dr. Eric Tedford, Tech­nical Lead for Fungicides for Syngenta, agrees that rusts of all kinds were very troublesome during the 2017 growing season. And there were other diseases as well.

“The most troublesome fungal diseases of corn in 2017 were gray leaf spot, Northern corn leaf blight, and rust — both Southern and common,” says Tedford. “None of these diseases are friends to growers.”

Ironically, he says, gray leaf spot disease was never a major problem in the U.S. until after the 1970s, when no-till practices became popular with grower-customers. “By not tilling infected plants under, the fungal pathogen that causes gray leaf spot could overwinter in the stubble and spores could infect plants the following season,” says Tedford.

As for what diseases should be on the radar for ag retailers and their grower-customers during 2018, Tedford says that this is hard to predict with any level of certainty. “That said, there are a few diseases that tend to occur every year such as gray leaf spot in corn and frogeye leaf spot on soybeans,” he says. “In many locations, it is more a matter of when they will come in and to what extent than if they will show up at all.”

Nick Hustedde, Technical Service Manager for FMC Corp., agrees that frogeye leaf spot will bear watching out for in soybean fields. “With more soybean acres projected in 2018, growers need to be aware of this disease, especially if they are going to plant soybeans after soybeans,” says Hustedde.

As for corn and wheat growers, looking out for rusts will likely drive 2018 fungicide use decisions, he adds. “Corn growers will need to keep an eye on the northward movement of Southern rust,” says Hustedde. “It has become a driver disease for fungicide use due to a heavy epidemic in 2016. In wheat, we will need to watch stripe rust’s progression northward, as university pathologists in the Mid-South have already reported fall infections.”

Product-wise, many suppliers are offering new options for 2018 to combat some of these expected crop diseases. For example, DowDuPont, in conjunction with WinField United, has Lumisena fungicide seed treatment. Featuring oxathiapiprolin, Lumisena has been shown to be effective in protecting soybeans against phytophthora, says Teri Otte, Marketing Manager for WinField United.

Another new product for phytophthora protection is Amplitude from Mar­rone Bio Innovations. Based upon a new strain of Bacillus amyloliquefaciens, this product can also guard against such diseases as white mold and fusarium, says the company.

Also, there’s Smart-B-Mo from BRANDT. According to the company’s Agronomy Manager Ed Corrigan, this is a foliar boron and molybdenum product that works in combination with fungicide applications to help plants resist diseases. “Boron improves the plants’ ability to flower, set grain, and improve nutrient utilization,” says Corrigan. “It is also critical in cell wall structure and improved crop stand-ability.”

Of course, as Syngenta’s Tedford points out, the ultimate driver for any disease developments during 2018 will tie to the same thing it always does — Mother Nature. “Weather is the key determining factor on disease development, so what happens in 2018 largely depends on the weather,” he says. “For plant diseases to occur, you need the presence of susceptible host plants, the pathogens that cause the disease, and weather conditions that favor disease development. Weather can also impact disease prevalence by slowing plant growth or requiring growers to replant fields. Mild winter conditions can also favor survival of overwintering fungal pathogens and enhance the earlier onset of diseases.”

The Resistance Movement

Unfortunately for fungicides, the specter of resistance is beginning to rear its ugly head. Back at the start of the 2010s, disease researchers began finding examples of frogeye leaf spot in crop fields that showed resistance to strobilurin-based fungicides. According to experts, frogeye leaf spot is one of the primary yield-robbing diseases to impact the soybean plant. By the end of 2012, tolerance by this disease to fungicide applications was confirmed in 44 counties spread out across eight states. By mid-2017, this type of frogeye leaf spot was found in 11 different states across the South, Midwest, and Mid-Atlantic.

“Fungicide resistance is a threat,” sums up HELM’s Bettner. “We should anticipate that resistant populations of plant diseases will increase over time with fungicide usage. Generally, resistance can be delayed or decreased with product rotation or through mixtures.”

Kaustubh Borah, U.S. Fungicide Product Asset Manager for FMC, agrees with Bettner, pointing to other diseases that could quickly head down the resistance path. “Southern rust is a disease to watch for resistance development in corn,” says Borah. “It’s a very prolific spore producer and an extremely aggressive disease, so there is lots of selection pressure taking place with fungicide applications with this pathogen.”

To fight back against resistant frog­eye leaf spot and other potentially resistant crop diseases, fungicide suppliers say that the agricultural community needs to start employing products featuring various active ingredients. “Using multiple modes of action across different classes of chemistries is key to resistance management,” says Borah. “FMC will continue to expand its footprint in fungicides with solo and pre-mix combinations of flutriafol, one of the most highly systemic triazoles. Flutriafol performs very well on frogeye leaf spot and in combination with a strobilurin to help reduce the selection pressure.” Currently, he adds, FMC offers flutriafol solo in its Topguard fungicide and with strobilurin pre-mixes in Preemptor SC and Topguard EQ.

Other suppliers have also taken this co-pack approach with their fungicides. For example, BASF’s Priaxor D features a combination of fluxapyroxad and pyraclostrobin along with tetraconazole. Another triple product option is Trivapro (azoxystrobin+propicona­zole+benzovindiflupyr) from Syngenta.

“Fungicide resistance is an extremely important concern,” says the company’s Tedford. “It costs hundreds of millions of dollars to discover, formulate, and develop a new fungicide, so development of resistance is not a trivial matter. This is one of the main reasons Syngenta has developed so many mixture products of fungicides with different modes of action. Take Trivapro, for example. By mixing three different broadspectrum active ingredients all with different modes of action, we are exponentially reducing the risk for resistance development.”

How much of a reduction? The numbers are impressive. “For resistance to occur, the fungi would need to undergo three simultaneous mutations for those modes of action,” he says. “This is highly unlikely.”

One of the newest such option on the fungicide block featuring multiple modes of action active ingredients is Helmstar Plus SC from HELM. According to the company’s Bettner, Helmstar Plus SC features a blend of tebuconazole+azoxystrobin, plus a specialized surfactant system and can be used for disease control in corn, soybeans, and peanuts. “As the threat of resistance continues to proliferate, growers have new technology such as Helmstar Plus SC, which contains two actives with different modes of action, to adopt as part of a disease resistance management strategy.”

Of course, as Bettner says, all of these products tend to work best when they are combined with a healthy dose of knowledge. “As a reminder to all, scouting the fields should not be overlooked,” he says. “This needs to be done on a regular basis to stay proactive in protecting crops against both new and common diseases, as they are likely to appear.”

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