Rain makes grain, the saying goes. But too much spring rain also means disease, and lentil crops are no exception.
Almost all pulse leaf diseases are triggered by rain and moisture in the canopy, said Dr. Sabine Banniza, plant pathologist with the Crop Development Centre. “Many need the rain in order to spread.”
So which diseases should farmers be guarding against in their lentils? Banniza outlined the top leaf diseases she sees in Saskatchewan during a Saskatchewan Pulse Growers webinar.
“The number one lentil disease we have in the province these days is anthracnose,” said Banniza.
Anthracnose causes beige or brown lesions. Those lesions are not very conspicuous, Banniza said, and so farmers and agronomists would have to look closely to see them. Once the disease is established, farmers will likely see leaf drop.
Those stem lesions can also girdle the stem, killing the plant above the girdle, she said. “And when this happens, you all of a sudden start seeing these dead patches in your lentil crop.”
There is anthracnose resistance in lentils, but that resistance covers Race One, the less aggressive strain. Race Zero is more aggressive and more common, and there is currently no resistance to it in cultivated lentil varieties.
Ascochyta blight used to be the top lentil disease in Saskatchewan. But the last serious outbreak was in 2005, said Banniza. That drop is a success story of lentil breeding program, she said.
“We’ve bred quite good resistance into almost all the lentil cultivars that are available now,” said Banniza. As a result, the ascochyta blight population “has just imploded and hasn’t really been able to come back.”
Stemphylium blight starts out as light beige lesions that coalesce. The whole leaf eventually turns brown. Farmers will also see leaf drop.
Spores are airborne, making it difficult to do field research on the pathogen, Banniza said. But the research they’ve done indicates that early to mid-flower infections may cause yield loss, seed stain, and seed infection.
However, stemphylium blight often rolls in late in the season. Those late infections probably don’t cause much damage, Banniza said. “And if it’s really late, it may actually work like a natural desiccant because it defoliates the leaves.”
White and grey mould
Sclerotinia white mould and botrytis grey mould are two different organisms. But they are “like sister and brother,” said Banniza. “They often show up together because they both thrive in the same conditions.”
These diseases are very recognizable because they grow on the outside of the plants, said Banniza. Cottony white mould on stems, leaves, flowers, and pods is sclerotinia, while fuzzy grey growth indicates botrytis.
Both diseases show up late in the season when canopies are dense and moist. Tall, lush lentil crops are more likely to suffer an infection. Lentils tend to lodge in those conditions, creating an even denser mat of biomass that doesn’t dry.
“And that’s when these two diseases really get going,” said Banniza.
Managing leaf diseases
Banniza recommends a four-year rotation to control leaf disease. Tightening the rotation raises the risk of building disease inoculum in the fields.
“And if you run into a year when conditions are conducive, you’ll see an earlier outbreak and a much more severe outbreak which is more difficult to control,” said Banniza.
However, that longer rotation is unlikely to reduce stemphylium blight because the spores are airborne, she added.
Farmers should also choose resistant cultivars when they can, she said.
Scouting is very important, said Banniza. The eight- to 10-node stage is the best time to apply fungicide, so scouting needs to be done before then.
Banniza said the management strategy is the same for several of the leaf diseases.
“So if you see lesions early on in your crop, and conditions are conducive to infection, it doesn’t matter whether it’s an anthracnose lesion or an ascochyta blight lesion or a stemphylium blight lesion.”
However, it’s a “different story” for sclerotinia white mould and botrytis grey mould, she said. Because those diseases develop in thick lentil stands, usually after canopy closure, fungicides don’t penetrate the canopy.
If a farmer is lucky, the fungicide will reach the top third of the canopy in those cases, Banniza said, but the disease is usually at the bottom. “So for these two diseases unfortunately fungicide is not a very good option.”
In fact, there are no great control options for sclerotinia white and botrytis grey moulds, she said.
“The best option is to manage your canopy. But that’s obviously very tricky because when you seed it, you don’t know what the growing season will look like,” said Banniza.
“If you knew it was going to be a wet year, you would probably try to seed at a slightly lower rate just to make sure the canopy is a little bit more open.”