A couple of years ago, a Saskatchewan farmer applied a fungicide to a lentil crop to control anthracnose — a common disease in the pulse crop.
After waiting for a period of time, he checked the lentils and noticed the fungicide wasn’t all that effective.
He told the fungicide manufacturer, BASF, about the problem. The company confirmed that the field had a type of anthracnose that was resistant to Group 11 fungicides — the strobilurins.
Insensitivity to fungicides is another way of saying the disease is resistant to fungicides.
BASF followed up that discovery with a survey of lentil fields in Saskatchewan. It found many fields had anthracnose that was resistant to Group 11 fungicides.
“You’re going to find some level of insensitivity throughout the province,” said Colleen Redlick, technical marketing specialist with BASF Canada.
“What we don’t know (yet), is what that’s going to mean… for the grower…. We’re not getting a lot of calls from growers. We’ve haven’t seen a lot of growers (who are) reporting a decrease in performance.”
That could be because lentil fields across Saskatchewan have a mix of anthracnose. Strobilurins will control one pathotype of the disease in the field, but not the other.
That’s the finding of a survey of lentil fields, done last year by Agriculture Canada, Saskatchewan’s ministry of agriculture and private agronomists.
“The most common result for a field is (that) some of the anthracnose was sensitive (effective) and some was resistant,” said Michelle Hubbard, a pulse crop pathologist with Agriculture Canada in Swift Current, Sask.
In many years, anthracnose is found across Saskatchewan. In 2018, it was detected in 74 percent of Saskatchewan lentil fields and 92 percent of surveyed lentil fields in 2019. The disease can cause leaf loss, yield loss and plant death.
With a mixed bag of anthracnose in most fields, it’s not easy for growers to make a decision about control, such as, should they use a Group 11 fungicide or not?
“These insensitive isolates (of anthracnose )… a Group 11 fungicide will have no impact on those isolates,” Redlick said in late May. “That doesn’t mean it will have no benefit on the field, as a whole, but there will be a portion of the population that has the genetic mutation for insensitivity.”
Some agronomists might tell growers to stop using strobilurins so the resistance problem doesn’t get worse.
But a fungicide that has a Group 11 and other modes of action, such as a groups 3 or 7, might make some sense.
“I think that’s where there’s a bit of differing opinions,” Redlick said.
“Group 11s certainly have a lot of benefits for growers, when we talk about things like plant health, standability.”
One thing is clear. Lentil growers shouldn’t apply a fungicide that contains only a Group 11.
Another recommendation is to use a fungicide only when it is warranted. That means scouting and assessing the risk. Things that affect risk include:
- Density of the plant stand.
- The number of days with rain over a 14-day period.
- Five-day weather forecast.
- Symptoms on the plant.
Those factors can be combined to generate a risk score, using a tool developed by Agriculture Canada that can be found here.
The reality is that anthracnose with resistance to fungicides is here to stay.
It will need to be managed, using crop rotations, thoughtful use of fungicides and perhaps intercropping.
Redlick believes it can be managed.
“We’re in a really good place right now in Western Canada, where we can get this messaging across about sustainable fungicide use,” she said. “And (we) still have those Group 3s and 7s as tools, to supplement the Group 11s.”