Given the wet springs and dry summers we’ve seen in recent years, Aphanomyces euteiches — Aphanomyces root rot — has become a real problem for pea and lentil growers.
First confirmed in Saskatchewan in 2012 and then in Alberta in 2013, the disease has been slowly creeping across the country, destroying crops in its wake. Making matters worse, the disease has the ability to live in the soil for up to 12 years where it continues to build up until environmental conditions are just right. Growers with Aphanomyces in their fields will want to take steps to minimize its impact.
The first step in managing any disease is identifying it, says Dr. Syama Chatterton, pulse crops pathologist, Agriculture and Agri-Food Canada. “Unfortunately, symptoms of the two types of root rots are very difficult to distinguish,” she says. Not only will fields that have experienced flooding or high levels of water saturation show symptoms that look like root rot, but Aphanomyces root rot also exhibits similar symptoms as Fusarium spp.
“If a grower suspects root rot in a field the best action is to send samples to a testing lab for confirmation of whether or not Aphanomyces euteiches is the causal agent,” says Chatterton. Seed-testing labs in Saskatchewan and Alberta, she says, offer this service.
No in-crop soluation
Once root rot has been diagnosed there is unfortunately no in-crop solution. There are no fungicides that can help manage root rots, says Chatterton. “Foliar-applied fungicides will not penetrate the soil surface to reach the roots and thus do not have activity in the roots,” she explains.
“Seed treatments have efficacy in reducing early season root rots caused by Fusarium spp., Rhizoctonia solani and Pythium spp., preventing seed-borne diseases. However, there are no seed treatment products registered for Aphanomyces root rot, and active ingredients found in registered seed treatments are not effective against Aphanomyces.
Without in-crop solutions, the only action growers can take is post-harvest or pre-planting. “Once it is confirmed that you have Aphanomyces root rot, decisions need to be made prior to planting your next pulse crop in that field,” she says, explaining that a field that is found positive for Aphanomyces will require a longer rotation of up to six years.
Beth Markert, seed growth specialist with Bayer CropScience, agrees. “A four-year crop rotation will no longer suffice,” she says.
Markert offers a number of other techniques that could help manage the disease. First, she says, clean all equipment before moving on to the next field. Opt for a healthy, high-germinating seed, good fertility and a heavy seeding rate in order to establish the crop early on.
“Although no seed treatment on the market can prevent Aphanomyces root rot, it is still recommended to use a seed treatment to prevent any other diseases coming in, as Aphanomyces root rot opens the plant tissue up for diseases such as Fusarium and Rhizoctonia to follow in it,” says Markert.
Although Aphanomyces root rot affects the entire legume family, peas have a different strain from lentils and chickpeas, so growers can switch from one crop to another. Finally, says Markert, avoid stressing the crop. ‘If you don’t need to spray, then don’t,” she says. “Fusarium and Aphanomyces like low pH fields. You could raise the pH in your field by putting a lime precipitate down for multiple years to break the disease cycle.”
“If you need to plant peas, then choose a field with good drainage and sandy soils so the water does not sit in your field too long, as Aphanomyces is a water mould,” Markert concludes.
Since Aphanomyces is relatively new to the Prairies, there have been almost no field trials focusing on potential management options that fit with the growing practices of the region. Chatterton and her team at AAFC have planned field trials to test the ability of soil amendments and seed treatments to reduce root rot severity for 2015 and 2016.