KANSAS CITY, MISSOURI, US — As the US Congress works toward funding research on reducing scab in wheat and barley, producers continue to refine farm management practices and soil inputs with the hope of mitigating the destructive viral disease known as fusarium head blight. 

The current farm bill, passed in 2018 and late last year through Sept. 30, funds fusarium head blight (FHB) research with $15 million in taxpayer dollars each year. The total comprises $8.6 million allocated to the US Wheat and Barley Scab Initiative (USWBSI) through the Agricultural Research Service (ARS) and $6.4 million allocated directly to the US Department of Agriculture’s ARS Base FHB Research Program. Letters sent last year to the House Committee on Agriculture, signed by dozens of agriculture groups, including the National Association of Wheat Growers and the North American Millers’ Association, requested the USWBSI budget be raised in the next bill to $20 million.

“Any flour miller would tell you that’s money well spent,” said Dave Green, executive vice president of the Wheat Quality Council. “Particularly for soft wheat and then the hard wheat in the eastern regions of spring wheat areas and the eastern regions of Kansas on the winter wheat side, fusarium is still a huge potential problem. Millers and farmers would probably list scab as the No. 1 research project.”

USWBSI’s $8.6 million allocation funds six areas of research. By far the largest (63%) goes to variety development and host plant resistance, followed by FHB management practices research (11%). Other areas include pathogen biology and genetics; food safety and toxicology; and gene discovery and engineering resistance. USWBSI-funded labs have evaluated more than 49,000 wheat and barley samples from 31 states for mycotoxins.

The group has conducted integrated management trials in 20 states to evaluate new fungicide chemistries for growers. Their breeding efforts for FHB resistant wheat and barley cultivars in 2022 resulted in the release of 29 germplasm varieties that were 69% moderately resistant to FHB. 

A major development is the FHB Risk Tool created and managed as a collaboration between the USWBSI, Kansas State University, The Ohio State University and the Penn State Center for Environmental Informatics. It’s an interactive map forecasting the risk for the disease during a specified assessment period based on such condition factors as localized rainfall. The group said 80% of the tool’s users credit it with helping increase crop profits through avoiding unneeded fungicide applications, highlighting needed applications to reduce disease losses and vomitoxin (DON) contaminations or influencing grain purchasing or marketing decisions. 

Root rot and stalk rot

Fusarium head blight — the formal name for scab of wheat and barley — causes root rot in wheat, maize and soybeans and stalk rot in maize.

There are several species associated with FHB, the most common being the fungal pathogen Fusarium graminearum. It reduces seed quality and yield due to discolored, shriveled “tombstone” kernels. That scabby grain is unsuitable for milling or feed use since it is often contaminated with trichothecene and estrogenic mycotoxins. FHB occurs when sexual and asexual spores, released from colonized crop residues, ride the wind and are deposited on florets.

FHB infects wheat and barley through the developing florets. The fungus then colonizes the developing internal grain tissues and presents dark brown areas as initial symptoms. The floret is subsequently bleached and the infection spreads internally and externally to adjacent florets across the entire wheat or barley head and down through the stalk, shriveling and bleaching the kernels and creating the tombstones.

“Half the kernels don’t develop and the other ones develop with a white-salmon pink chalky color, and it is certainly a big-time yield reducer,” said Green, a former director of quality control and laboratory services for ADM Milling. “More importantly, scab reduces the milling value. Millers are very attentive to vomitoxin as those crops come in with fusarium and they at harvest time quickly have to put on standards to keep from getting overwhelmed by it. There are a lot of instances where the farmers can’t deliver or they’re delivering with a big discount, so it’s more than a yield issue, it’s a milling issue.”

To a degree, scab is a flaw that can be overcome in the blending process.

“For elevators and even the millers to some extent it’s OK to blend some zeros with a four-part-per-million, for example, and be well below the legal limit,” Green said. “There is blending going on but it’s certainly at the farmer level where they’re going to take the big discount.”

Wheat and barley producers in many cases can adequately control FSB with management strategies, often including fungicide applications. Still, FHB continues to present a challenge to US grain growers due to the evolution of fungicide-tolerant strains of Fusarium graminearum and the lack of highly resistant wheat and barley cultivars. 

Farm management practices have proven successful in lowering the incidence of FHB and slowing its spread. These practices include selecting resistant cultivars as they become available, managing crop residues via tillage, irrigation and the use of efficient disease forecasting models. But those practices cannot manage FHB entirely when climatic conditions are favorable for the disease. 

Fungicides are the principal means to control the disease, but when conducive weather conditions bring on high FHB pressure, more than 60% disease incidence can result despite the presence of fungicide applications, according to a peer-reviewed paper published in August by Michigan State University agronomists. Recent research has indicated silica added to soil as a fertilizer has been shown to reduce the prevalence and intensity of FHB breakouts. Also, tests have shown using a combination of multiple fungicides during a growing season offers more efficacy for full-season FHB control. 

“Scab seems to be one of those diseases that they just can’t seem to find a cure for, but they do find more resistance,” Green said. “Breeders have increased the resistance in the wheat and that has been coupled with the lower cost of fungicides compared to the 1990s for example and so that combination of just resistance in the germplasm and fungicide use has been what has kept this problem tamped down. There are control measures between the varieties and the fungicides but the risk of it returning in wet years is still pretty great.”

Fhb’s impact on agriculture

In the past 30 years, FHB has become the plant disease with “arguably the greatest impact on US agriculture and society” and “has reached epidemic proportions in the United States, causing yield losses and price discounts from reduced seed quality,” USDA agronomists said in their overview of the disease. 

The first outbreaks of FHB were more than 100 years ago. Thirty-one states reported its symptoms in 1917, a year when 288,000 tonnes of wheat were estimated to have been lost to the disease. FHB first grew prevalent in the 1990s, a decade in which US agriculture lost more than $2.6 billion to FHB, including more than 500 million bus of wheat valued at about $2.5 billion and about $400 million worth of Midwestern barley, the USDA said.  

“Fusarium tends to be associated with corn production, because it survives over winter on the stubble, so there tends to be a lot of inoculum around,” Green said. “As the Corn Belt moved into the Red River Valley and into western Minnesota, that’s when we started noticing it being more of a problem in the Great Plains. It started showing up as corn started moving through the West, and with no-till farming, there’s a lot more trash on the fields than there used to be.”

A 2020 research paper on FHB control indicated US wheat farmers lost $17 billion worth of wheat from 1993 to 2014. The losses often are regional since moisture, humidity greater than 90% and moderate temperatures (from 59° to 86°) during the growing season play a role in FHB presence. For example, Southeastern wheat growers in Maryland, North Carolina and Virginia lost more than $13 million to FHB in 2003. 

Outbreaks in Asia, Canada, Europe and South America have increased the threat to the world food supply in recent decades.

Less prevalence in 2023

The 2023 growing season saw less prevalence of the disease. Experts from 31 states indicated most growers saw no impact to grain yield or quality from FHB, according to the “2023 Fusarium Head Blight Disease Impact Update,” an annual update issued by the USWBSI.  At the same time, scab popped up in late-planted crops and organically managed small grains in select states where FHB is generally not a concern. Most growers were able to lessen the impact of scab through fungicide applications and management practices. 

In the Great Plains, a lack of moisture during a second-straight drought-plagued growing season limited disease pressure, but localized rain events created conditions that allowed some FHB development that ultimately led to discounts or rejection of supplies at grain elevators. The problem emerged in isolated areas of western Nebraska and that state’s panhandle, where dry conditions make FHB a rarity. Discounts and grain rejection due to FHB were more common in northwest Kansas in 2023 as large rainfall totals met high relative humidity just as the hard red winter wheat crop was flowering in late May. 

“Severe scab in this region of Kansas is atypical and most varieties are susceptible or highly susceptible,” said Kelsey Andersen Onofre, a wheat and forage crops plant pathologist at Kansas State University, in the Impact Update.

In the Southern Plains, trace levels of FHB symptoms were noted in Oklahoma and in some irrigated Texas fields where wheat rotated in following corn. Colorado growers, likely due to cost and lack of historical prevalence of scab, largely eschewed preventative fungicide applications despite a prediction of high risk by the FHB Risk Tool. Eastern Colorado fields received above-average rainfall in 2023, and FHB was ultimately detected in 13% of samples tested at Colorado State University’s Colorado Seed Lab. 

A hot, dry Northern Plains growing season mostly prevented FHB in small grains, though it was found in 4% of wheat fields in North Dakota, which in 2023 seeded 5.6 million acres to hard red spring wheat, 750,000 acres to durum wheat and 130,000 acres to winter wheat, the Impact Update said. Jochum Wiersma, a University of Minnesota extension agronomist, said timely fungicide applications mitigated most scab and vomitoxin (DON) risk in the state, including in southwestern North Dakota durum, which was considered under high disease risk in July. Both diseases had minimal presence in Minnesota and South Dakota, and none in Montana, Wiersma said. About 5% of North Dakota barley fields (840,000 acres were seeded for 2023 harvest) had FHB symptoms, but it was largely avoided as heading took place during a low-risk period, Wiersma said.

In the Central and Southern states, drier-than-normal conditions were unfavorable for FHB and DON, and Illinois, Indiana and Ohio fields had a low or undetectable presence of the disease. The same result was seen in Kentucky, where farmers frequently seed soft red winter wheat following corn in a no-till system in which fusarium-infected corn stalks and debris serves to inoculate moderately resistant wheat varieties treated with the most efficacious fungicides, according to the Impact Update. 

Though the primary production areas for the three largest US wheat classes mostly escaped large-scale FHB-related yield losses, other regions saw more issues from the disease in 2023. While most of Georgia was free of FHB, the disease was prevalent in four southwestern counties, especially late-planted fields, said Alfredo Martinez-Espinoza, University of Georgia small grains extension plant pathologist. In the Northeast, spring grains were planted in a timely fashion while drought prevailed into early July. But the region received record-setting rainfall that month, and moisture kept coming through September. Crops had slow, uneven or poor germination and highly variable FHB and DON issues, agronomists with the University of Maryland and Virginia Tech said.

“The levels of DON from samples submitted from the Northeast to our testing lab have been very low in winter wheat and much higher in spring grains, especially spring wheat,” said Heather Darby, a University of Vermont extension agronomist, in the Impact Update.

“Much like the 2023 growing season weather patterns, DON has been extremely variable even within regions and grain types,” Darby said after lab testing samples of corn, einkorn, spring barley, spring wheat, winter wheat, triticale and rye.

Will FHB be a problem in ‘24?

Upcoming forums promise continued discussion and shared scab research.  The USWBSI plans a live, free “scabinar” from 10 a.m. to noon (CDT) on March 13. Registration and a link to watch a previous Scabinar are at scabusa.org/scabinar.  

Early this summer, international fusarium experts will lead the 23rd Fusarium Laboratory Workshop covering morphological characters for strain identification, molecular characters for strain identification, species concepts, mating type and crosses, VCG analyses, strain preservation and mycotoxins. The event is set for June 23-28 in the Plant Pathology Department on the Manhattan, Kan., campus of Kansas State University. 

The 2024 National Fusarium Head Blight Forum is set for Dec. 8-10 in Austin, Texas. 

But first, wheat scouts from all areas of the wheat value chain will see first-hand whether the Southern Plains’ emergence from two years of drought increases fusarium presence during the annual Hard Winter Wheat Tour.

In early March, it’s too early to tell, Green said.

“Rain that Kansas has had to date is not going to be the indicator,” he said. “It tends to be the rain we get in May or late in the season where the plants are heading and that opens them up to the fungus. It’s very much a two-week time period where people watch for scab appearance. It doesn’t matter how wet it is now or how dry it is now, when the wheat gets to a heading stage and we get this flourish of inoculum, that’s when the problem starts.”