Crop disease experts take stock of 2020

Your provincial roundup of pulse and soybean diseases, what to watch for this year and emerging threats

The openings on the roots of soybean plants infected by SCN may cause the plant to be more susceptible to the development of root rot and seedling diseases.

From east to west, pulse and soybean growers face disease challenges, and last year was no different. For example, producers from all three provinces struggled with aphanomyces root rot in peas and lentils, Manitoba’s soybean farmers were warned of increased cases of soybean cyst nematode (plants are more susceptible to root rot and seedling disease in these fields), and a mysterious health issue affected chickpea crops in Saskatchewan for the second year in a row. As disease experts take stock of 2020, these were just a few of the issues showing up in farmers’ fields.

Manitoba

As of recent years, soybean has become one of the more widely grown crops in Manitoba. Root and stem diseases are the main concern. Soybean is a relatively new crop to the province and, as such, disease pressure is still quite low.

Why it matters: New threats are emerging while the incidence and spread of established diseases continue. Understand what’s happening in your province to inform disease management decisions.

“But we are expecting it to develop as we continue to grow soybeans,” says Cassandra Tkachuk, production specialist, Manitoba Pulse and Soybean Growers. “We know that stem and root diseases can have the biggest impact on production and quality.”

Stem diseases such as sclerotinia root and stem rot haven’t been a real problem in soybeans in Manitoba yet, but the risk is greater for those who have tighter rotations of host crops. “It is also largely weather dependent,” adds Tkachuk. “Risk can be there across many years, but only expressed if conditions are ‘right,’ around the time of flowering.”

Northern stem canker is also starting to appear more often, she says.

Fusarium is the No. 1 root pathogen across all pulse crops, including soybeans. Fusarium is almost always present, but not always at high levels. An opportunistic pathogen, it will often set in when other diseases infect the plant.

Exclusive to soybeans, the pathogen Phytophthora has been making an appearance as well, although at very low levels in 2020. Like Aphanomyces, it likes and depends on wet environmental conditions.

There has been quite a jump in pea acres in Manitoba as of late, making aphanomyces root rot a top concern. If the pathogen is present in the field, growers should aim for a six- to eight-year break period.

“Although we have fewer pea acres than other provinces, it might even be a greater concern here due to wetter conditions from time to time,” says Tkachuk.

She also reminds growers that long rotations have other benefits too. They prevent volunteer plants from becoming weeds, help diversify herbicide programs and provide opportunities for soil fertility management and nutrient building.

New threat in the neighbourhood

Tkachuk warns producers to watch out for soybean cyst nematode (SCN) in their soybean crops. The openings on the roots of soybean plants infected by SCN may cause the plants to be more susceptible to the development of root rot and seedling diseases.

While the pest was identified in the province for the first time in 2019, it is currently not a big problem. However, as soybean production continues, so too will SCN’s presence, says Tkachuk. Four fields have tested positive for SCN in four out of 18 municipalities so far.

“There were only four fields and at very low levels, so consistent with recent establishment,” she adds.

Tkachuk is encouraging farmers to scout randomly for SCN symptoms. Once above-ground symptoms are evident, growers can expect up to 30 per cent yield loss. She recommends scouting high-risk areas, such as low spots and field approaches.

To determine if the pests are present, soak the roots of plants taken from random locations in your field in water and look for small, lemon-shaped cysts on those roots. Note that cysts will be smaller than root nodules.

Key management strategies for SCN include rotation and using resistant varieties. “The way it works with that pest is if you’re rotating away from its main host, which is thankfully only soybeans, you’re just starving the pest,” said Tkachuk. “The longer the break period, the less it can survive and the less it will hurt your yield.”

Tkachuk also warns growers some soybean varieties have lost resistance to SCN because of how widely they’ve been used in past years.

Scouting calendars for pulse and soybean crops in Manitoba are available at the Manitoba Pulse & Soybean Growers website.

Saskatchewan

Saskatchewan pulse crop growers had their share of disease pests in 2020. In peas and lentils, the biggest issue is root rot. Aphanomyces is the main pathogen of concern and Fusarium is a close second.

Sherrilyn Phelps, agronomy manager at Saskatchewan Pulse Growers, says there’s a lot of information on the organization’s website that explains how to reduce the risk of aphanomyces root rot for 2021. For example, field choice, rotation and testing for the pathogen are important, she says.

Chickpea fields in 2019 and 2020 showed unusual symptoms in early to late July across southern Saskatchewan during flowering and early podding. Initial symptoms started as wilting and chlorosis of the top growing point. photo: Sherrilyn Phelps

Anthracnose continues to be the disease of concern in lentils. It was a problem for growers in 2020, and once it starts appearing, says Phelps, it can be very aggressive.

Saskatchewan Pulse Growers has been involved in a project that’s evaluating the level of anthracnose insensitivity to strobilurin fungicides.

“There was a concern brought forward this past spring regarding high levels of resistance and we are just in the process of getting the samples from this summer analyzed through the Ag Canada station at Swift Current with Michelle Hubbard,” says Phelps. “We don’t have the results from the over 100 samples that were submitted through the survey (last) year, but managing anthracnose that has potential resistance to the Group 11 herbicides is a real concern going forward.”

Aschochyta rabiei, which causes aschochyta blight, remains the pathogen of concern in chickpeas, especially as producers begin to see insensitivity to Group 11 fungicides. Phelps says there’s information on the Saskatchewan Pulse Growers website about how to manage aschochyta as well as fungicide insensitivity.

Mystery disease

A second issue affected chickpea acres last year, but agronomists don’t know what it is yet. What agronomists are currently calling a “chickpea health issue” was found in almost every chickpea field in the province in 2020. Fields with greater incidence of infection saw some yield loss, while less-infected fields were not affected yield-wise. In some cases, the health issue delayed maturity, which led to quality issues.

“We’ve had it now for two years and we’re working to try to identify what it is,” says Phelps. “It could have a link to a disease of some sort, but we don’t know yet.”

The best advice at this point includes reducing risk by watching for residual herbicides, application timing and potential nutrient deficiencies and managing for disease.

In fababean, Saskatchewan Pulse Growers identified three foliar diseases of concern — botrytis chocolate spot, stemphylium blight and alternaria leaf spot.

“We still don’t know the disease impact on yield, but there’s some research projects underway evaluating that,” says Phelps.

In dry beans, blight has been the main concern. There were not many issues in soybeans in 2020, besides the drier conditions in August, which affected yields.

Alberta

Similar to Saskatchewan and Manitoba, aphanomyces root rot is the biggest issue in lentil crops in Alberta, although lentil acreage is very localized. In a wet year, the biggest issue in lentils is sclerotinia.

“Sclerotinia moves into the lentils right around flowering, the canopy closes and then we’re done,” says Robyne Bowness Davidson, Alberta Agriculture and Rural Development pulse research scientist.

Just like their neighbours to the east, Alberta’s pea growers are also challenged by aphanomyces. Alberta tends to have wetter, heavier soils that are higher in organic matter, so when aphanomyces moves in it can be quite devastating, says Bowness Davidson. Adopting best management practices, including planting high-quality seed into clean fields, are the only solutions for aphanomyces, she adds.

Although fababeans are susceptible to diseases, the crop faces no real issues in Alberta. Fungicides are available for any diseases that do occur.

In Alberta, chickpea acreage is much lower than it is in Saskatchewan. The good news is in this province, the mysterious health issue observed in Saskatchewan was not found in 2020.

About the author

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Melanie Epp

Melanie Epp is a freelance farm writer.

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