Mississippi State University (MSU) researchers have identified a fungi-based disease that has been plaguing soybean crops in the state in recent years.
Soybean Taproot Decline produces yellowed leaves on soybean crops like other diseases, but is a year-round menace.
“This disease has eluded all of us, and I think the reason for that is it has been misdiagnosed as a number of similar diseases we have seen before in soybean, such as sudden death syndrome,” Tom Allen, MSU Extension Service's plant pathologist and Mississippi Agricultural and Forestry Experiment Station (MAFES) researcher, said. “It’s not on a single fungicide label, and it has never been reported as an issue in soybeans. I’ve been looking at this ever since I got here in 2007.”
The best time to spot Soybean Taproot Decline is during the vegetative stage of growth, when the plants are first emerging, according to Allen and MAFES researcher Maria Tomaso-Peterson.
“If you grab a soybean plant and pull it out of the ground, and you leave the vast majority of the taproot there, or you have a portion of the taproot and you break it, and it snaps and sounds dry, you have taproot decline,” Allen said. “The organism that causes this essentially produces a dry rot and rots the taproot away. The base of the stem will look black, indicating fungal growth.”
Preliminary data on tested fields shows that there is, on average, about 18 percent harvest yield loss because of the fungus.
“As we looked at several fields across the state and conducted trials of our own, it became evident that this disease has the potential to be a significant yield reducer if allowed to go undetected,” Allen said. “There are severe cases that we’re observing in some instances, but it is not yet a major issue in general. Not every field where taproot decline occurs is going to have an 18 percent yield reduction. I would say most fields that have this particular disease would have minimal amounts of yield reduction as a result.”
MSU faculty will continue testing Soybean Taproot Decline in fields, greenhouses and laboratories.