Diseases continually threaten yield and profitability of soybean, corn, wheat and sorghum crops in Louisiana. That’s why research to minimize damage has continued to be an important part of LSU AgCenter research efforts conducted at multiple research stations and on farms.

The LSU AgCenter is working on various approaches to improve soybean resistance to many diseases.

Trials consisting of 30-45 entries — mainly advanced breeding lines and commercial varieties — have been conducted since 2016 across Louisiana and the Midsouth, and scored for Cercospora leaf blight. This research, done under the leadership of top breeders, including AgCenter soybean breeder Blair Buckley and other universities, has identified some commercial varieties and soybean germplasm that showed resistance to Cercospora leaf blight.

“Breeders have already begun utilizing the material to incorporate into elite lines for variety development,” said AgCenter plant pathologist Trey Price.

Official soybean variety trials at multiple research stations are rated each year for naturally occurring diseases and can be used as a tool for producers when making planting decisions. Results can be found on the Louisiana Soybean Varieties page LSU AgCenter website.

Taproot decline has been an emerging disease problem, and researchers at the Macon Ridge Research Station and in other Midsouth states have looked at many fungicide seed treatments and in-furrow sprays as potential management options.

“We’re seeing some promise with a few specific fungicide modes of action and are moving forward looking for consistent efficacy over multiple years and locations,” Price said. “We aim to determine which products producers can use at planting and at which rates they are most effective against the taproot decline pathogen.”

In addition to at-planting fungicide trials, 2019 marked the third year of taproot decline rotation and tillage studies. AgCenter results showed that rotation to corn, cotton or grain sorghum and conventional or minimum tillage lower disease incidence and severity in soybean.

Louisiana’s hot, humid conditions also help create the perfect environment for foliar diseases. Many foliar fungicide efficacy trials in 2019 identified products effective on Cercospora leaf blight, frogeye leaf spot and aerial blight.

“We’re seeing activity with a number of SDHI compounds along with newer generation DMIs on Cercospora leaf blight and aerial blight,” Price said. “This has been a welcome development, as products containing QoI materials have been ineffective for a number of years due to fungicide resistance in multiple pathogen populations.”

In the event of a disease outbreak, fungicide applications, if warranted, may preserve yield and quality, he said. “We can manage most foliar soybean diseases reactively, which means we don’t have to treat every acre with prophylactic applications. With judicious use of the effective products, we can prolong their usefulness and delay fungicide resistance development.”

Future soybean studies will continue to identify and develop resistant soybean varieties, as well as keep up with a constantly evolving fungicide industry. There are also knowledge gaps concerning lesser-known diseases in Louisiana like Southern root-knot nematode, reniform nematode, target spot, Septoria brown spot, Southern blight, charcoal rot, sudden death syndrome and red crown rot, Price said.

Official wheat variety trials were rated for resistance to leaf rust, scab and stripe rust.

“The big one is wheat scab, and we’re looking for varieties with resistance to scab as well as the best fungicides for applications at flowering,” Price said.

AgCenter researchers conducted many foliar fungicide trials in corn, where Northern corn leaf blight and Southern rust developed to moderate levels.

There are many fungicide options, and the most effective ones were identified. These results may help growers find less-expensive treatments that are just as effective.

“Some farmers have been in the habit of applying fungicides regularly, even when there’s no disease,” Price said. “The key is to determine whether you need to apply or not because our data shows no yield bumps or other benefits when spraying nondiseased corn.”

Besides doing research, Price and other pathologists help growers identify what’s in their fields and on their plants.

“I constantly get photos, lab samples and field calls from growers, consultants and industry asking about problems on their plants, and probably 30% to 40% of the time it’s not disease at all,” he said.

Grain sorghum official hybrid trials for 2019 indicated varying susceptibility to multiple diseases. Results at one site indicated a good set of anthracnose ratings, Price said.

Fungicides are not effective on head blights; therefore, identifying hybrids that are resistant to head blights is important, he said.

Researchers completed four foliar fungicide trials for sorghum and found they were effective on a disease complex consisting of anthracnose, target spot and zonate leaf spot. Overall, foliar fungicide treatments in cases of moderate to severe disease lowered the disease severity and preserved yields.

“The two biggest diseases for sorghum are anthracnose and target spot,” Price said. “Typically, foliar fungicides that work for anthracnose might not work for target spot. That’s why disease identification is key.”

In-furrow and seed treatment fungicides were not effective on stand or yield of sorghum.

“Sometimes negative data is useful,” Price said. “In this case, it shows growers what not to do.”

The success of maintaining control of diseases in soybeans, wheat, corn and sorghum depends upon continuing research that keeps pace with the constant onslaught of existing and emerging diseases and an evolving industry.

“Our research trials are designed to generate practical information that farmers can use to stay in business,” Price said. “That’s the mission of the AgCenter and that’s what farmers pay us to do.”

The AgCenter has developed and maintains a disease management guide for all plants grown in Louisiana in the Louisiana Plant Disease Management Guide.

This story is featured in the Louisiana Soybean and Grain Research and Promotion Board 2020 Report.

Corn that was fungicide-treated in field tests by the AgCenter. Photo by Trey Price

Nonfungicide treated corn with Northern corn leaf blight in field tests by the AgCenter. Photo by Trey Price