Heed rotations, switch pulses to keep root rot at bay: expert

Soil born disease | The pathogen chokes the roots, depriving the plants of nutrients

Growers need to start using best management practices to stop the spread of the pulse industry’s version of clubroot, says an expert.

Aphanomyces, a highly virulent root rot disease that attacks annual and perennial legumes, is making its way across the Prairies.

The pathogen, which was first confirmed in Saskatchewan in 2012, was discovered in seven fields across five counties in Alberta this year.

Beth Markert, Bayer CropScience’s SeedGrowth specialist for southern Alberta, said aphanomyces is reminiscent of clubroot.

“It has a lot of similarities.… You can kind of expect to see the same thing,” she said.

It is a serious soil-borne disease that targets peas, beans, lentils and alfalfa and has caused 30 to 50 percent yield loss in Saskatchewan fields.

Primary symptoms are found on the plant roots , which appear grey and water-soaked at first and then turn honey or blackish brown.

The pathogen chokes off the root system, reducing uptake of nutrients and water.

Secondary symptoms include yellowing of the cotyledon and death or discolouration of leaf tissue and wilting foliage.

Farmers mistakenly believe aphanomyces causes death and decay of seedlings. What it does is stunt the growth of seedlings, rendering them less competitive against weeds, bugs and disease.

It also acts as a conduit for other diseases because it can penetrate any tissue cell in the plant.

“When the infection starts, it makes it a lot easier for other diseases such as fusarium or rhizoctonia to enter the plants,” said Markert.

“Lots of people are mistaking aphanomyces for fusarium, simply because fusarium will follow aphanomyces in afterwards.”

She advised farmers to clean off equipment when moving it from a field suspected to contain the root rot pathogen.

“I can see in the near future that the same tactics will have to be put in place for aphanomyces as there is for clubroot,” she said.

Pulse growers who want to avoid the water-based mould should select sandy fields that drain well rather than clay soil that is thick and compact and tends to hold moisture.

Rolling peas compacts the soil, creating a nice home for the pathogen. Growers who want to roll their peas should do it when the soil is dry and cooler than 25 C.

Pulse growers who suspect they have aphanomyces should consider extending their rotations because the disease can live in the soil for up to 12 years. Switching between pulses is also advised, since each one is affected by a different strain.

Growers are advised to use healthy seed with high germination rates and have their soil tested.

There are no seed treatments for aphanomyces, but growers who suspect it is present in their fields should apply seed treatments to combat fusarium and rhizoctonia.

Growers should avoid applying pesticides to a crop infected with aphanomyces because it will further stress an already stressed crop.

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