Mustard Cover Crop Controls Charcoal Rot

KANSAS - Apr 8/19 - SNS -- Researchers at Kansas State University have discovered using mustard seed as a cover crop in the state helps reduce the incidence of charcoal rot, resulting in improved soybean yields.

Farmers in southeast Kansas have problems with high levels of charcoal rot, a fungus that chokes the plant's recycling system so that it cannot get nutrients or water, ultimately killing its roots.

"Charcoal rot tends to be worse in hot, dry conditions, and that's what happens in Kansas in the summer," notes Gretchen Sassenrath, a research agronomist at the Southeast Research-Extension Center in Parsons. "We get hot and dry and the charcoal rot grows and infects our soybean plants."

There are chemical treatments for charcoal rot, but Sassenrath and colleagues Chris Little, Xiaomao Lin and Kraig Roozeboom were interested in finding natural agents to counter the effects of the fungus.

Mustard seed contains high levels of glucosinolate, which gives processed mustard its tang, but in the soil it acts as a bio-control for charcoal rot fungus."

Sassenrath added that the species used in this study is different from a weedy mustard cover crop that is better off sprayed and killed with a herbicide. Over two growing seasons, the K-State researchers showed that planting mustard seed as a cover crop reduces the incidence of charcoal rot in the soil.

Mustard Seed Improves Soil Health

"Mustard seed has actually been shown in other systems to improve the overall soil health," Sassenrath said. "The approach I am taking is more of a holistic approach. For example, if a person is healthy, they might come into contact with people with a cold, but they won't get sick themselves because they are overall healthy.

"In the same way, if we can support the soil in a positive way with positive microbes and things that they need, it improves the overall soil health and the soil will be better able to manage diseases that are naturally there all the time."

The researchers also tested various management options, including planting soybeans into standing mustard seed; mowing it; or tilling it to incorporate residue into the field. Their key finding: leave the mustard crop as intact as possible.

"If we just rolled the mustard cover crop over the top of the soil and planted straight into that, that was the best in terms of reducing the charcoal rot," Sassenrath said.

The group is continuing its work, including looking at effects on yields due to sudden death syndrome and soybean nematodes. "It's been suggested that the mustard can control those or have some impact on preserving yield when those are present," Sassenrath said. "But we don't know for sure.

"Again, it's a holistic approach to soil health and getting more bushels per acre. There is a lot of promise with this mustard seed as being a mechanism or a tool that can be used to improve the overall soil health."