DISEASE. It seems like the topic is all around us these days. But what farmers and researchers alike know is that it doesn’t just seem like disease is everywhere. It is everywhere.
The thought can be overwhelming, and because these organisms are often out of sight, it’s also easy to ignore their existence. But Dr. Kaitlyn Bissonnette, assistant Extension professor in plant sciences at the University of Missouri in Columbia, spends a lot of time at the microscope looking at infected plants and knows the impact of diseases can’t be discounted.
“Disease will always be present at some level. It’s just about minimizing the amount,” said Bissonnette, a third-generation plant pathologist. “When we’re talking about plants, disease literally blows in the wind. It overwinters on plant residue and in soils.”
What’s more, she said healthy plants make for healthy hosts, creating an “arms race for survival.”
“When we think about healthy plants with high nitrogen, those plants tend to actually be more susceptible to disease,” Bissonnette said. “Because as much as plants like nitrogen, so do fungi. While we’re trying to create as much yield as we can per acre, we’re also feeding the pathogens. They’re trying to grow and survive as much as the plant is trying to grow and survive.”
When it comes to controlling disease, it all comes down to management, she added. And it starts with knowing the land and its history.
R.G. Kirby, who farms 750 acres in Fayette, Mo., understands the importance of managing his crops closely for disease and other threats to their performance. In fact, he relies on Charlie Ebbesmeyer, MFA Crop-Trak consultant and local agronomist, to be another set of eyes in the field. Ebbesmeyer has an advantage here. He grew up just a couple of miles down the road and began working on Kirby’s farm at the age of 14 during the summer. Kirby also participates in MFA’s Nutri-Track program, and Ebbesmeyer helps with that soil sampling.
“We’re patch farmers,” Kirby said. “We farm a patch here and a patch there, but Charlie knows these fields. I don’t have to tell him how to get around.”
Ebbesmeyer not only knows where each field is, he knows how it’s been managed. Kirby’s operation is largely no-till. While the practice has made a positive difference in the soil organic matter, Ebbesmeyer knows disease can persist on those residues, creating additional need for disease deterrence.
Kirby often interseeds clover hay into wheat or uses wheat as a cover crop in rotation with soybeans. Thanks in part to his Crop-Trak consultant’s watchful scouting, last year Kirby harvested some of the best wheat he’d ever seen. But the season didn’t start that way. Early on, Ebbesmeyer found evidence of fusariam head blight in the crop and brought it to Kirby’s attention.
“I started to see small amounts scattered throughout his fields,” Ebbesmeyer said. “With the wet spring we had last year, I knew it was a good possibility for this disease to have damaging effects on his crop.
We went in with a timely application of the full rate of Miravis Ace (fungicide), and I didn’t see any issues grow past what was already there. I looked at a few other fields in the area, not on R.G.’s farm, that didn’t receive a fungicide, and they were hit hard with head blight. Because of this, along with his incredible yields last summer, we know that the fungicide application was the right call for his farm.”
Kirby and his wife, Marilyn, are both retired schoolteachers who have always farmed in addition to their previous full-time employment. The couple has participated in MFA’s Crop-Trak program for the past 10 years.
“It’s an important part of our operation. We don’t use any chemicals unless Charlie tells me to in his scouting report,” Kirby said. “I see those reports every week, usually the day he’s out here.”
Now in their 70s, the Kirbys have started the process of transitioning the farm to the next generation. They have two daughters, one who lives in Kansas City and another who lives in South Carolina. Crop-Trak has provided the added benefit of helping them understand what’s happening on the farm from a distance.
“With computers and phones, and the eventual help of a farm manager, they’ll be able to continue to run this,” Kirby said. “They ask questions based on the scouting report. I also share it with the sharecroppers we work with and our financial institution, so they know what we’re doing out here, too. They all have a vested interest in our farm.”
START WITH THE SEED
Environmental factors and certain cultural practices can decrease disease risk, Bissonnette said, but the best protection is seed selection.
“Disease management, first and foremost, is about understanding when to plant a resistant hybrid or variety,” she said. “Most farmers have an idea of field history, especially for obvious diseases such as sudden death syndrome or sometimes soybean cyst nematode, if they’ve done sampling recently.”
But, she emphasized, some of the more subtle diseases, such as frogeye leaf spot or gray leaf spot, may be harder to recognize just driving by the field.
“The best resistance is genetic resistance, so that’s where we start,” said MFA MorSoy Product Manager Tommy Lee, who gathers information on disease tolerance from both breeder data and MFA’s own field observations. “If a grower has a problem with sudden death year after year, he could use a seed treatment to help with that issue. But seed treatments are chemical, so it’s eventually going to break down and wash out of the root zone, leaving the plant susceptible. So, starting with good genetic tolerance and then building upon that is the way to go.”
It’s an age-old tale—resistance—a tug-of-war between the plant and pathogen. Every species is programmed to survive and overcome. But through science, humans have intervened, using plant breeding as a way to give the crop an advantage.
“With plants, there are some types of resistance in which a single gene will work on a particular pathogen,” Bissonnette said. “But nowadays, we often see multiple genes acting on a specific pathogen, which results in more durability, less ‘failure in the field,’ if you will, and less chance of the pathogen overcoming that resistance. That’s why knowing what diseases are in certain fields and using that information for variety or hybrid selection is the first line of defense.”
Crop rotation and proper row spacing are among the factors that play a key role in mitigating disease pressure. Conversely, irrigated crops may suffer increased risk due to many fungal pathogens’ propensity for damp conditions.
“It really depends upon the disease,” Bissonnette said. “Opening up the rows and increasing air flow in the canopy can help with many diseases. There are others that favor certain crop rotations. For instance, tar spot tends to show up in continuous corn production, and in the Bootheel region of our state, target spot occurs in both cotton and soybeans.”
Target spot isn’t the only disease to cross species, she said. The pathogen of fusarium head blight infects both corn and wheat, while charcoal rot exists in both corn and soybeans.
“Southern blight also has something akin to 200 host species,” the plant pathologist said. “That’s mostly in horticultural production, and not so much in field crops, but we occasionally see it. Rotation is definitely one of the things you have to consider when planning for the next season.”
BACTERIAL? VIRAL? FUNGAL? PARASITE? NONE OF THE ABOVE?
Pathogens take many forms, but more than 75% are fungal. Some require a living host and will only survive for a single season in Missouri, while others may be structured for much longer lifespans outside their plant hosts.
Identifying diseases often takes a trained eye. Signs and symptoms may overlap or resemble other agronomic issues like herbicide injury, and often multiple diseases may be present at once.
“Rarely do I walk into a field and only see one disease,” Bissonnette said. “If the environment is conducive for one disease, it’s usually conducive for many. Diseases are opportunistic. Once a plant becomes stressed, it can open up the avenue for other infections to move in.”
Because pathogens can be transmitted by different types of organisms, knowing what’s present in the field affects how it can be treated. And, with fungicide resistance on the rise, that knowledge is more critical than ever, Bissonnette warned. When fungicide is necessary, proper management is about using multiple modes of action and really understanding when to spray.
“If it’s a bacterial or viral pathogen, don’t spray a fungicide,” she said. “Like herbicide resistance management, the more we expose a pathogen to fungicide, the more likely resistance is to develop.”
For fungicide application, timing is key, emphasizes MFA District Agronomist Shannon McClintock. It was the sole focus of the presentation he gave at MFA’s annual Training Camp, held virtually this year. In that presentation, he laid out the specific application windows for common diseases in soybeans, corn and wheat.
On Kirby’s farm, Ebbesmeyer knew the window was brief for treating the fusarium head blight.
“You don’t have a lot of time when dealing with wheat,” he said. “Depending upon the season, weather and chemical, you can have anywhere from as long as a week to as little as two days.”
That quick turnaround is just another factor in the Crop-Trak equation, Kirby said.
“It’s the prime reason he [Ebbesmeyer] is out here,” he said. “It’s of paramount importance that we get timely applications. He’s tied to that spray rig, too, so when he sees something, he’s able to make a phone call and get someone out here.”
Bacterial diseases are a different ballgame, Bissonnette said. When it comes to the control of these pathogens, there’s little to be done outside of cultural control methods such as row spacing and residue management to decrease the bacteria present in the fields, she explained.
Additionally, while viral diseases can and do show up in Missouri fields, she said most usually don’t pose a significant threat to yield.
“Viral organisms are most often transmitted through insects, so management of those pathogens is more about insect control,” Bissonnette added. “There are not a lot of viral diseases that I am concerned about, and most of them don’t cause significant yield loss.”
Nematodes often get lumped in with diseases, but they’re actually a pest that causes disease. Much of Bissonnette’s recent research centers around soybean cyst nematodes, tiny parasitic roundworms that are one of the largest contributors to yield loss in soybeans. These nematodes work their way into the root of a plant and establish a feeding site, leaving a cyst on the root itself. Once established, it leaches water and nutrients from the plant, causing the plant stress.
Bissonnette said there are even pathogens that fall outside these categories that are neither fungus, bacteria, virus nor parasite.
“They’re called oomycete pathogens,” Bissonnette said. “Things like pythium and phytophthora are considered fungal-like organisms, and we control those with specific seed treatments. There are no foliar applications that can be made for those.”
Again, Bissonnette stresses that a field’s history can help predict the field’s future.
“What it comes down to is if you don’t have your field history, it’s really hard to implement effective management practices,” she said. “Getting out into the field, scouting and knowing what’s going on helps you to have a better feel for what types of yields you might see and what your potential can be for years to come.”
It can be a balancing act to produce a profitable crop while fighting against factors such as diseases that are seemingly beyond control, but MFA has the products, services and expertise to help producers maintain and regain that balance. For more information, contact your MFA Agri Services or AGChoice location or visit https://mfa-inc.com/PrecisionAg/Crop-Trak.
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