Rotations best ammo in pulse disease war

Peas, lentils and some alfalfa crops are susceptible 
to a root rot for which there is no treatment

Extending rotations is still the best way to combat a virulent root rot disease that is taking its toll on pea and lentil crops, says a pulse crop expert.

Sabine Banniza, a pathologist with the University of Saskatchewan’s Crop Development Centre, said there are no effective seed treatments or fungicides for dealing with aphanomyces.

Growers have to rely on agronomic practices for combating the disease, and lengthening rotations is at the top of the list.

Research from France, where pea growers have been wrestling with the disease for a decade, suggests rotations should be stretched out to six or eight years between susceptible host crops on fields where there are high levels of the disease in the soil.

Susceptible hosts include peas, lentils and some alfalfa crops.

Growers intent on keeping a pulse crop in the rotation might want to consider fababeans, soybeans or chickpeas, which all demonstrate good resistance to the disease.

“I realize lentil and pea prices have been quite good whereas chickpea prices haven’t, so there are definitely economic reasons why a producer may not choose to grow (chickpeas),” Banniza said during an hour-long webinar on root rot organized by Saskatchewan Agriculture.

“But I think you have to think about the long-term sustainability of your fields in terms of lentil and pea production.”

Chickpeas can be grown in the brown and dark brown soil zones. Modern varieties have much improved resistance to ascochyta blight than ones from 10 years ago.

Fababeans are a new pulse crop option for the Prairies. They grow well in wet soil and have good resistance to aphanomyces. They are sensitive to foliar diseases such as aschochyta blight, botrytis and anthracnose ,but there are seed treatments for those diseases.

Soybeans also perform nicely in wet conditions and there are well developed markets for the crop, but they can be grown only in areas with plenty of heat units.

Crop Development Centre breeders who are trying to incorporate resistance into pea lines are looking to France and the United States, where researchers have been screening varieties for 10 years.

The centre has access to U.S. varieties that have shown far better resistance than Canadian peas.

“The French have selected some lines as well, but they’re not yet really willing to share them with us until they have released their first varieties to farmers.”

She thinks aphanomyces resistant lines could be on the market in Western Canada within three or four years.

There is evidence from European research that growing brassica species or oats can decrease aphanomyces levels in the soil.

The glucosinulates in the brassica plants and other anti-microbial properties in oats decrease root rot populations.

Unfortunately, that rules out canola, which is low in glucosinulates.

Banniza said the European re-search was based on green manure crops, which are worked into the soil when the anti-microbial chemicals are at their peak. Anti-microbial activity also lasts longer in Europe because of climatic differences.

“It is still something we should probably explore here in Western Canada as well, as it may help contribute to controlling aphanomyces root rot,” she said.

Growing peas and lentils on lighter soil with good drainage is another good agronomic practice because aphanomyces thrives in wet and compacted soils. It is why the disease has become so prevalent after five consecutive years of soggy springs.

Farmers will also want to assess their soil nutrient situation. Fields may be low in nitrogen if the previous crop was a bumper crop, if the fall was dry or if the spring was cold and wet.

Pulses fix their own nitrogen, but they need a little nitrogen in the soil in spring to get going or the seedlings will be stressed and vulnerable to attack from root rot.

Banniza said there should be 15 pounds per acre of available nitrogen.

“If your soil doesn’t have that, maybe it’s good to make sure it gets it through fertilizer,” she said.

Growers in infected areas should use good quality seed with high germination levels and a limited amount of cracked seeds.

“Cracks are usually the open door for a pathogen,” she said.

As well, seed treatments are a must because they will kill root rot pathogens other than aphanomyces.

Banniza said some farmers have the mistaken belief that apanomyces is only a pea disease, but lentils are equally susceptible.

The disease was found in 53 percent of the pea samples and 57 percent of the lentil samples analyzed by the Saskatchewan Agriculture Crop Protection Lab last year.

It has been discovered in pea and lentil fields across Saskatchewan, where it has caused significant yield losses.

“We know it’s very, very widespread,” Banniza said. “That suggests to us it has probably been in the province for quite a while.”

Marlene Boersch, managing partner of Mercantile Consulting Venture, is forecasting a minimum 10 percent increase in pea acres and 13 percent hike in lentils this year.

Banniza said pea and lentil prices are attractive, and growers in areas where root rot hasn’t been too bad will likely increase plantings.

However, farmers in heavily infested areas may be forced to consider alternatives.

Contact sean.pratt@producer.com

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