Lentil disease resists control

Wetter areas of fields with high loads of anthracnose are more likely to be hot spots of resistance to fungicides. | File photo

A Saskatchewan Agriculture survey has found that anthracnose is present in most lentil fields in the province

Many, if not most lentil crops in Saskatchewan, have anthracnose that is resistant to Group 11 fungicides — the strobilurins.

That’s one of the findings of a survey, done in 2020, where Ministry of Agriculture staff and agronomists collected samples of diseased lentils throughout Saskatchewan.

“It (fungicide resistance) is widespread across the province,” said Michelle Hubbard, a pulse crop pathologist with Agriculture Canada in Swift Current, Sask. “There is an excellence chance they (lentil growers) have some insensitivity in their fields, already.”

Insensitivity to fungicides is another way of saying the disease is resistant to fungicides.

Hubbard led the survey of lentil fields in the province, as she wanted to understand the prevalence of anthracnose that is resistant to Group 11 fungicides.

Anthracnose is a common fungal disease of lentils.

“It has the potential to infect all plant parts and can result in pre-mature leaf drop, yield loss, and even plant death,” SaskPulse said in a newsletter from last June.

In 2018, anthracnose was found in 74 percent of Saskatchewan lentil fields and 92 percent of surveyed lentil fields in 2019.

For years, growers relied on fungicides to control anthracnose. But that strategy became more challenging in 2019.

“At the end of the 2019 field season, insensitivity to Group 11 strobilurin fungicides was confirmed in Saskatchewan,” SaskPulse said.

The finding was based on the observation of some growers, who noticed that fungicides weren’t effective against anthracnose.

But scientists didn’t understand the scope of the problem or the variability across the province.

So, in 2020, Ministry of Agriculture staff and others took samples from more than 100 random lentil fields, in dozens of municipalities. They submitted the diseased plants to the Agriculture Canada lab.

Doing lab work during COVID-19 has been challenging and technicians still have many samples to analyze. But Hubbard did provide some preliminary findings.

Very few lentil fields have anthracnose that is sensitive to strobilurin fungicides.

Most fields were a mixed bag.

The strobis controlled anthrac-nose, in some plant samples from a particular field. But in other samples, from the same field, the fungicide was not effective.

“The most common result for a field, is (that) some of the anthracnose was sensitive and some was resistant,” Hubbard said.

“And there are some fields that are totally resistant (to strobis).”

There was some difference between Crop Districts across Saskatchewan, but Hubbard needs to further study the data before sharing that information.

Hubbard wasn’t surprised about the variability within lentil fields because anthracnose can be a “patchy” disease — with areas of severe anthracnose and areas with lower disease pressure, in the same field.

“It seems reasonable the evolution of resistance could be patchy as well,” she said.

If there is a wetter area of 40 acres, with high loads of anthracnose, the disease is more likely to mutate and develop resistance to fungicides in that area.

“We also collected data on individual sites, on whether they were high spots in the field. Low spots in the field. Or neither,” Hubbard said, to see if there’s a correlation between field location and fungicide resistance.

In the future, Hubbard and her colleagues will release a more comprehensive report on their sampling program and anthracnose resistance to fungicides in Saskatchewan. This summer, Ministry of Agriculture staff and industry agronomists will continue to collect samples of diseased lentils.

In the meantime, growers can take steps to manage the problem

A SaskPulse presentation from this winter said:

  • Growers should do a risk assessment, based on rainfall, the weather forecast, plant stand and disease symptoms, before using a fungicide. Only spray when the risk is sufficiently high.
  • Know the product and the active ingredients. Don’t use a fungicide that only contains a Group 11. Most fungicides have a combination of Group 11, Group 3 and Group 7 modes of action.

As well, growers should scout after application to see if the fungicide is controlling the disease. And they could consider using a biofungicide to introduce another mode of action.

In the longer term, lentil breeders and plant pathologists hope to develop varieties with resistance to the more prevalent and virulent races of anthracnose.

In Saskatchewan, Hubbard is more interested in agronomic solutions, like intercropping, to control anthracnose.

She plans to study an intercrop of camelina and lentils, to see if that deters the disease.

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