There may be more than one reason to plant mustard in 2022.
Some producers will hope to springboard off 2021’s shortages and grow food-grade mustard for domestic and international markets.
But others might choose mustard for a less conventional reason: as a biofumigant cover crop to help quash soil-borne pests and diseases.
Mustard contains glucosinolates (GSLs), organic compounds that when plant fibers break down are converted to isothiocyanate, a gas that is toxic to many soil-borne pests.
In the Maritimes, a growing body of research points to the efficacy of mustard as a biofumigant against the pathogen causing verticillium wilt (part of a complex causing potato early dying disease), as well as common scab, wireworm and root lesion nematode.
A still-larger library of international research highlights the effectiveness of mustard as a biofumigant in a range of crops in greenhouse trials.
Syama Chatterton is a research scientist with Agriculture and Agri-Food Canada in Lethbridge. She’s the project lead on a study looking at the use of mustard as a biofumigant against aphanomyces root rot of pea.
“There’s a lot of background literature showing that mustard works really well in greenhouse trials. The residues are good at reducing the spore load. So we wanted to bring it out to the field,” she says.
Chatterton’s study, which will run through 2022, compares three varieties of mustard, including a hot mustard bred with high levels of glucosinolates, a white mustard (Sinapis alba) and Indian mustard (Brassica juncea).
In 2019, the first year of the study, the team compared four treatments. In one, the mustard was allowed to grow as a full-season crop before being harvested. In another, it was taken down at peak vegetative biomass, flail-mowed and used as a green manure. They also compared tillage to zero tillage.
“So what we did was after we grew those crops in one season, the following year — 2020 — we planted peas to see if there was an impact on root rot reduction and on pea yield.”
The researchers didn’t observe any immediate effect on root rot severity at any of the study’s three locations (Lethbridge, Lacombe and Saskatoon), although they did report a pea yield boost in Lacombe.
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The mustard sequence was planted again in 2021 — 2022 will be the final pea year of the study, and by then Chatterton hopes the data will tell a stronger story. Weather is likely a contributing factor for the less-than-standout results so far.
“2019 was a dry year for establishment, so that’s why we saw a better response in Lacombe, where it was wet, versus Saskatoon and Lethbridge,” she says. “Because it was dry when we tilled the biomass into the soil, I wouldn’t expect there to be lots of microbial activity. Unfortunately, 2021 was also really dry, so (the must went in) under the same conditions. Then, 2020 was really wet, ideal conditions for pea rot.”
potato research
Most mustard biofumigation is used in potatoes to manage a variety of soil-borne pests and diseases.
One recent Manitoba Horticulture Productivity Enhancement Center (MHPEC) study looked at the use of mustard biofumigation crops to manage verticillium wilt in potatoes. The study aimed to develop a set of agronomic practices to maximize production of glucosinolate in mustard green manure.
What the researchers found was that planting date, the presence of cereal stubble and seed treatment significantly influenced mustard yield and characteristics. Earlier-seeded mustard had higher yield, population, height and early-season vigor — and “substantially more” biomass, particularly if treated with a seed treatment for flea beetle protection.
The researchers recommend flailing versus mowing to achieve highest levels of isothiocyanates. The sooner residues can be incorporated in the soil, the better — they recommend incorporating within 10 to 15 minutes, as they say up to 80 per cent of isothiocyanates can volatilize within 20 minutes of chopping.
Further experiments and results are pending.
In Charlottetown, the PEI Potato Board has also been running mustard biofumigation trials for the past few years.
Ryan Barrett, the research co-ordinator and agronomy lead for the PEI Potato Board, is the lead on one project that began in 2020.
“In potatoes, there are a few soil-borne diseases that can be very impactful on the crop and we don’t have good pest control products for — like verticillium wilt, and common scab, which is caused by a bacterium,” he says . “If you have land in rotation with potatoes, it’s common to find those (diseases.) Some years you can get away without much of a problem, and some years you can have a big problem, especially if it’s dry or the crop is stressed .”
Barrett says Agriculture and Agri-Food Canada research scientist Christine Noronha has led projects looking at suppression of wireworm, and there’s “good local data” supporting its efficacy. But more work is needed looking at mustard’s biofumigation effect on rhizoctonia root rot and other pathogens.
In the new trial, a mustard blend with high levels of glucosinolates was planted in commercial fields alongside a conventional brown mustard, as well as check crops. The following year, those fields were planted with potatoes. The cycle will repeat this year.
The mustard blend contains hot mustard and a small amount of arugula, which in theory works as a “trap crop” for root lesion nematode, to keep the pest in the top layer of the soil profile, Barrett explains. About seven weeks after planting, the mustard has enough biomass but hasn’t yet gone to seed; it’s flail-mowed into a fine chop and incorporated into the soil using vertical tillage equipment.
“You leave that soil for about two weeks for the fumigation to occur, then you go in and plant a cover crop,” says Barrett.
The team hopes to assess the impact not only on soil-borne nematode counts, but also soil health and yield in the following year, he adds. They’ll also complete an economic analysis to assess whether the cost of taking a field out of production is worth it for producers, or whether it makes sense to put portions of fields, or fields with the highest pest levels, into mustard.
Economic considerations
It’s common for PEI growers to plant non-commercial crops such as forages or service crops like buckwheat, pearl millet or radish in the year before potatoes. But mustard requires more management than most of these—such as fertilizer application, and equipment to do the chopping, says Barrett.
The value proposition would improve if mustard could be harvested, but the jury’s still out on whether harvesting mustard and incorporating the stubble has the same impacts on pests. One project at the Eastern Canadian Oilseeds Association is looking at this question.
According to its website, ECODA’s project will evaluate the agronomic and economic benefits of a harvestable mustard crop in rotation with potatoes. Data isn’t yet available.
Chatterton says the original goal of her research project was to assess the effect of mustard as a shoulder-season crop, planting it in the fall, getting some biomass and then, with winterkill, hopefully producing enough isothiocyanates to achieve biofumigation. This would mean fields would not have to be taken out of production for a whole season. But the team attempted this over two dry years and couldn’t get the mustard established, she says. She notes this might work better in Ontario or Quebec than it did in the Prairies.
They’ve also looked at intercropping mustard and peas. “We didn’t see impact on disease severity, but we saw a fairly significant yield increase to the peas. Yield is responding, although not necessarily disease severity — but it’s hard to tie disease severity to yield anyway,” she says.
Aaron Mills, a research scientist with Agriculture and Agri-Food Canada in Charlottetown, says there’s a “groundswell” on mustard biofumigation research. He’s running his own trial looking at the benefits of mustard in rotation with potato. I can’t share data yet. But there are other trials in the works.
“We’ll see more of this (research) in the future,” he says.