Producers are increasingly planting cover crops to improve soil quality, help manage weeds or pests, and provide livestock forage – but is root rot a possibility when pulses, specifically peas and lentils, are added to improve the nutrition of the mix? 

Frankie Crutcher, plant pathologist at Montana State University’s (MSU) Eastern Agricultural Research Center (EARC) spoke about root rot disease and cover crops at EARC’s annual field days in 2023.

“You are probably aware that, currently, insurance does not allow you to grow cover crops and peas and lentils and then follow it with commercial peas and lentils. The reason for that is disease,” Crutcher says. “I wanted to actually address this because there doesn’t seem to actually be any real scientific evidence that this is an issue.”

Crutcher says root rot has been limiting pulse production, especially when diversified producers want to grow cover crops with peas and lentils and have a crop that will improve their feed mixes.

Crutcher set up a cover crop with pulses study with Darren Boss, superintendent of MSU’s Northern Ag Research Center (NARC); Peggy Lamb, research scientist at NARC; and Kate Vogel, co-owner of North 40 Ag. Vogel designed the cover crop mixes for the study.

“We wanted to make sure that the mixes met our needs to answer our questions, but we were also somewhat realistic to what our producers would grow,” she says.

The group had four cover crop mixes and used two planting dates, an earlier planting date and a late planting date. They changed the mixes to make them more of a warmer weather-friendly mix.

“In year two of the experiment, we come back on the top of that soil and planted peas and lentils and then we were evaluating root rot and taking soil samples and doing biomass in years one and two,” Crutcher says.

Specifically, the group isolated Fusarium from the roots so they could “look at what species are in there, how virulent they are, and kind of ask deeper questions with that.”

“Because I’m a plant pathologist, I want the most disease possible in one of my treatments, so we have a forage pea only. We would expect that planting pea after pea, we would have the most severe root rot,” she says.

In 2022, Havre had a severe drought, and that affected the cover crop trials.

“I assure you that our cover crops are much more robust this year than they were last year,” Crutcher says.

One of the treatments used a “suppressive mix.”

“Whether or not that’s suppressive is still debatable, but we wanted to add in some crops that have been shown to have antimicrobial activity and lower root rot and other systems,” she says.

To do that, they included rapeseed, other brassicas, and oats in the cover crop mixes.

“Those crops make antimicrobial compounds in the roots and at least in the studies in Canada, have lower root rot,” she says.

In another treatment, called an alternate host mix, they added other crops in the mixes, such as vetch and clover, which could be hosts for some of the pathogens that they were interested in finding. In the late planting date treatment, they substituted barley for millet to the mix.

“We would expect that the root rot would be worse in this mix than in the suppressive mix,” Crutcher says.

Another treatment they used was the benign mix. Crutcher said they would not expect an effect either way from the benign mix because there was not anything suppressive and there weren’t any suppressive hosts in it.

“The benign mix is composed of soybeans, cowpeas, collards, flax and safflower, things that either aren’t hosts but also don’t really have suppressive ability,” she saiys

Crutcher said 2023 was a good year to be a plant pathologist because she was seeing a lot of disease due to the rainfall, which was heavy at times. It helped with having more real results to show producers.

“It’s been a good year to be a plant pathologist. I can tell you the reason why I don’t have a lot of the results to show you today is because this is a large amount of work and I really want to thank my field crew this year,” Crutcher says.

Some observations:

  • The lentils across the board had higher disease incidents and severity than the peas did.
  • The later planting date treatments had worse root rot than the earlier planting dates.

“It has been shown in many other studies that when planting late, especially with Fusarium, you’re going to see more root rot,” she says. “Later planting tends to have more disease because it has to do with soil temperatures and optimal soil temperatures for infection.”

  • There was a small amount of residual herbicide damage in Havre in 2023 and they saw worse root rot than Crutcher would have expected.
“We suspect that the root rot might be tied to the residual herbicide damage. Other research has shown that herbicide residuals can cause worse root rot,” she says.

Crutcher said they found Ascochyta blight on peas for the first time in 2023 on the research farm.

“I have gotten reports from other people that this is a problem in their fields, which I’ve never really seen in this area before, so I just kind of wanted to bring it up,” she says. “It’s commonly confused with bacterial blight and the big difference here is the spotting on the leaves. With Ascochyta blight, you get these little spots with these little structures that occur in rings, and you need to spray.”

Crutcher recommends if producers have Ascochyta blight of peas and want to use a strobilurin, to ensure “you tank mix it with another ingredient because you’re going to get resistance to that active ingredient rather quickly. Always make sure that you’re using it with another active ingredient that is effective against Ascochyta,” she says.

The fungal pathogen that causes Ascochyta blight was found to have widespread resistance to the strobilurin class of fungicides, and since then, researchers and companies have been working on developing better solutions and management practices.

Crutcher said producers who have been growing peas or lentils for four or five cropping seasons in fields could be at risk for Aphanomyces root rot.

“The Schutter Diagnostic Lab at MSU is now doing soil testing for it and there are companies out of Canada doing that, as well,” Crutcher says.

Root rot caused by Fusarium species is becoming a major problem in the pulse growing regions of Montana, and seed treatments for that are “very effective.”

“I always recommend getting a seed treatment with multiple modes of action and an insecticide in it because healthier plants get less disease across the board. But for Fusarium, seed treatments definitely make a difference. Make sure you are adding something for pythium root rot,” she says.

Crutcher said producers who may have been thinking on putting pulse crops on former sugarbeet fields should be concerned about certain diseases.

“Both chickpea and lentil are highly susceptible to sugarbeet rhizoctonia. We were seeing 70 percent losses or greater, even with a seed treatment,” she says. “Peas still get disease, but they seem to be more tolerant, so peas would be the way to go.”

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