MSU Researchers Work To Resolve New Soybean Disease

LAURA HOUGH SMITH

STONEVILLE, MISSISSIPPI

There’s no quick fix to manage a relatively new root disease of soybean—taproot decline—caused by the soilborne fungus Xylaria necrophora. Mississippi State scientists, along with colleagues throughout the Mid-South continue to research answers for the fungus. 

“The soybean disease can be observed early in the plant’s development; however, soybean farmers and agricultural professionals are generally more aware of the disease’s appearance during the pod-filling stages,” said Tom Allen, MSU Extension specialist and scientist in the university’s Mississippi Agricultural and Forestry Experiment Station, or MAFES. 

Complicating the matter is the appearance of this particular fungus on annual plants. Traditionally, members from this genus of fungi live on dead or dying organic matter without harming plants and have been reported on trees ... which are perennial plants. 

Researchers are uncertain how a seemingly harmless fungus turned into a pathogen that, in severe cases, can result in 10- 30% yield loss. 

“I think we have allowed this fungus to build up over time on residue, and, as a result, we have observed the fungus moving into a new system,” Allen said. 

MAFES researchers first identified the disease in 2007 in and around the Delta town of Inverness with only a few fields exhibiting infected plants. 

“Now it appears to have progressed over time, and we’re seeing larger areas in single fields and a greater number of fields with infected plant material throughout much of Mississippi,” he said 

Early lab research focused on the causal organism that produced symptoms. Current research seeks to understand the efficiency of seed and in-furrow fungicide treatments. 

“We would expect seed treatments to be effective based on the timing of infection; however, they aren’t as effective as we need,” he said, noting that seed treatments offer protection for only a short period of time after planting. “So far, we haven’t identified anything that is effective because the fungus is so new, and it’s only been observed in a limited geographic area.” 

Soybean taproot decline has been reported in Alabama, Arkansas, Louisiana, Mississippi and Tennessee. To date, the disease has not been observed north of Tennessee. Allen and his Mid-South colleagues have spent over five years studying the disease and have established suggestions for producers. 

Research has indicated that tillage helps break down residue. However, scientists are studying more intensive forms of tillage to determine how it impacts the disease. 

In addition to tillage, crop rotation may be beneficial, seed treatments will provide some assistance, as well as choosing varieties that are tolerant to the disease, Allen added. 

“Move your A/B line so that you're not planting in the exact same spot each year,” he said. “That’s another big issue. We keep forming beds and planting in the same spot, and in continuous soybean situations we are planting into last year’s infested residue.” 

MSU plant pathologists at the Delta Research and Extension Center in Stoneville in collaboration with colleagues from adjacent states are conducting laboratory tests to understand the efficacy of fungicides, as well as seed and in-furrow fungicide trials. Scientists also will continue with tillage and rotation tests and variety screenings. 

“We’re not going to have an answer overnight. It’s going to take a lot of years and a lot of research to combat this disease system. There’s not a quick fix, but we’re working on it day in and day out, to give producers more effective management strategies.” 

For more information about taproot decline, contact Tom Allen at tallen@drec.msstate.edu or 662-402-9995.  ∆

LAURA HOUGH SMITH: Mississippi State University