Early results are in, and the recommendation is to get your pea and lentil seed to a testing lab, ASAP.
At the Top Notch grower meeting in Moose Jaw sponsored by SaskCanola, SaskFlax, and the Saskatchewan Pulse Growers, Saskatchewan’s provincial plant pathologist, Barb Ziesman, talked about the preliminary seed test results from Saskatchewan seed tests this winter.
Seeding healthy seed is essential to getting your crop off to a good start. “You want to make sure you’re selecting healthy seed with low disease levels,” Ziesman said.
When you’re getting your pulse seed tested for germination, have the lab test for disease as well. “Pathogens on the seed can cause seedling blight, but also root rots,” Ziesman said. Disease will cause seedlings to be less vigorous. “And, if they’re less vigorous, they’re more stressed.”
The charts below and further down show the numbers reported by three Saskatchewan labs, showing their preliminary test results.
The first column for each disease shows the percentage of PFS: pathogen-free samples. That is, the percentage of samples submitted to labs that were not infected. The higher this number the better. As Ziesman explained, “This means that 20 per cent of the lentil samples that were submitted had levels of anthracnose.”
The second column for each disease shows the mean (average) percentage of infection. In this case, 0.9 per cent. In the case of anthracnose, if the mean infection is above 10 per cent, “you should be thinking about using a seed treatment.”
For field peas, ascochyta could be a big problem this year. Seed infected with ascochyta can develop seedling blight. As shown in the table, only 21 per cent of the samples submitted were free of the ascochyta pathogen. “That means 80 per cent of the samples had some level of ascochyta species on the seed.” (For the math fanatics out there, this means you have a four in five chance of having an infected seed lot, based on these preliminary results.)
The ascochyta infection levels are also high, with a mean (average) preliminary level of 4.9 per cent, as shown in the table. This means many farmers will be in that grey area where you can still use the seed, but you should probably use a seed treatment. “Our general rule of thumb is that you should be using a seed treatment between five and 10 per cent,” Ziesman said. If your field pea seed has an infection level above 10 per cent, “maybe look for another seed lot.”
These high levels of infection are not surprising, as root rot symptoms were observed in 59 per cent of lentils last year, and 53 per cent of peas.
Ziesman pointed out that we often refer to root rot as “root rot complex” because there’s often more than one organism involved. While we focus on aphanomyces, fusarium species can be involved too. “These two groups of organisms work together synergistically,” Ziesman said. This means that if both problems are present, you’ll see more disease and higher severity than if there was just one of them present.
Having both fusarium and aphanomyces does not mean you just have more of the same. You have two different biologies working against you. Fusarium species are true fungi. “This means that some of our fungicides are going to be effective against them.” But aphanomyces are not fungi at all. They’re actually oomyces, or water moulds. A lot of fungicides are not effective against these organisms.
Because there are two different types of organisms, there are two host ranges. Fusarium has a wide range of hosts, from pulses to canola. Aphanomyces has a much narrower range of potential hosts.
“Having root rot does not mean you’re going to have more fusarium head blight, but if you have a cereal crop that has a lot of fusarium head blight, it might mean you have a higher risk of root rot.
“We used to talk about fusarium root rot versus aphanomyces root rot,” Ziesman said. The two diseases have different symptoms, and the results can look very different in the field. But it’s not usually that easy to tell the two types of infections apart. Even experienced pathologists can have difficulty differentiating the two diseases in the field, Ziesman said, because there is often more than one pathogen involved. If you want to identify your particular problem so you know exactly how to best deal with it, you are going to have to send your plants to a lab for testing. “You might want to know if it is aphanomyces, because management changes with aphanomyces.”
Why us? Why now?
Why are root rots causing so much trouble in recent years?
There are a couple of factors at work. First, we’ve been growing peas and lentils on the Prairies for a long time. This has given spores a chance to build up. If you’ve been growing lentils and peas in your fields for 40 years, you’ll have a higher chance of getting root rots.
Second, we’ve had a lot of wet years in the recent past, which also gives infection a chance to shine. Both peas and lentils are stressed under wet conditions. And when plants are stressed, they’re more likely to become infected. “Anything that stresses the plant is going to increase its risk of infection,” Ziesman says. This results in a higher likelihood of infection.
Crop rotations will affect your chances of having root rots. If you’ve been growing that crop only every four years, the spores will have had less opportunity to build up in the soil.
Compaction is also an issue. “We see higher severity and more root rot in areas of the field that are compacted. Compaction is going to hold more moisture, but it’s also, again, going to cause more stress for that plant.” Compaction creates a zone where root rot can thrive.
Choosing the right field
One way to lower your risk of developing root rot is to choose the right field. “Make sure that you choose fields that are lighter, or drier fields,” Ziesman said. Choose fields that have good drainage, and coarser soil. Ideally, choose fields that have no history of root rots.
“If you have a field that has aphanomyces, the recommended crop rotation is six to eight years away from peas and lentils. In heavily infested fields, we’re looking at closer to that eight years.”
But don’t be alarmed. Ziesman is not saying you can’t put a pulse crop in your rotation. “We’re not talking about all pulses. We’re really talking about peas and lentils,” she said. Peas and lentils are the most susceptible, and produce the most oospheres when infected. But as shown in Table 3, pulse crops like soybeans or fababeans are not susceptible to aphanomyces. You can still grow a pulse crop on fields where you may have had root rot in peas and lentils in the past. GN