Tackling Disease in Pulse Crops

With warmer winters and wet springs, disease tends to crop up

by Jane Caulfield

Disease in pulse crops can lead to major crop loss and have devastating results for producers. In Saskatchewan, root rots caused by fungi and fungal-like pathogens are the most prominent early season diseases in pulses. In 2016, 97 per
cent of pea fields tested were positive for the fungus Fusarium avenaceum. High levels of other pathogens, such as Pythium ultimum and Aphanomyces euteiches were also present.

“Plant diseases can be caused by living factors, such as fungi or bacteria, and nonliving factors such as adverse environmental conditions,” says Barbara Ziesman, Plant Disease Specialist for the Saskatchewan Ministry of Agriculture (SMA). “It is
important to determine what the cause of the disease is before management can be effective.”

When talking about plant diseases, researchers and experts refer to the “disease triangle” — a trio of factors that come together to create an ideal situation for disease to occur. Presence of pathogen, plant susceptibility, and environmental conditions all play a contributing role in the development and movement of disease, but experts believe the environment is often the driving force for disease development.

“Even if the pathogen that can infect the host, such as the fungal spores, is constant and the same variety is grown, there will be some differences in disease levels due to differences in the environmental conditions,” says Ziesman.

The Problem with Wet Feet

Many pathogens that affect pulse crops, such as Aphanomyces, need a lot of water to grow and spread. This means that an excessively rainy spring can cause a lot of problems and frustration for producers.

“Peas and lentils are more sensitive to excess moisture as they do not like wet feet,” says Sherrilyn Phelps, Agronomy Manager at Saskatchewan Pulse Growers (SPG). “Some pulse crops, such as soybeans and faba beans are more tolerant of higher
moisture conditions.”

With the exception of last year, the past few growing seasons in Saskatchewan have been abnormally wet, which, when combined with shorter rotation periods and increased inoculum in the soil, increases the risk of plant stress and disease at any point during the growing cycle.

“Any time a plant is stressed, they are more susceptible to disease,” says Phelps. “If the soil is a heavier texture or if there are cooler temperatures during the early season, the germination process can slow down, stress the plant, and can lead to seedling diseases.”

“Plants will show signs of yellow and reduced nodulation and root growth under excess moisture conditions,” says Phelps.

Other causes of plant stress include shortened rotations, soil compaction, and nutrient deficiency.

Understanding each impacting factor and having some knowledge about the various pathogens themselves, can help producers make crop-saving decisions and develop disease management plans.

Managing Disease

One of the most effective ways to deter in the development of seedling diseases in pulse crops is to ensure that disease free seed goes into the field. This means getting the seed tested for both quality and the presence of pathogens.

“Getting seed tested before planting can help producers determine whether or not that seed should be used,” says Ziesman “It can also help the producer determine if a seed treatment should be used and assist in developing a management plan.”

Certified seed, according to the Federal Seeds Act, only needs to meet standards of germination and purity but not all diseases. This is why experts suggest producers get seed tested by an accredited laboratory or ask to see the lab certificate before purchasing.

“Planting pulse seed that is free of seed-borne illnesses is the primary way to limit the introduction of pathogens into the field,” says Ziesman.

If some pathogen is present, producers can use seed treatments. But these treatments tend to only be effective for three to four weeks after seeding. Crop rotation can be used to break disease cycles and prevent the build-up of the pathogen within a field.

“Planning crop rotations is important activity during the winter months,” says Phelps. “With peas and lentils, if the desired field has had issues in the past then it is a good idea to stick to at least a four-year rotation.”

If a field has a history of Aphanomyces root rot or has tested positive for the pathogen (Aphanomyces), then the rotation should be even longer.

“If there were problems on the field the last time pea or lentils were grown, then growers should be moving to a six-to-eight-year rotation for these crops,” says Phelps.

Both Ziesman and Phelps mention that SPG and the SMA produce a variety of fact sheets and resources designed to help producers develop disease management plans. The more producers can do to prevent disease or stop the spread of disease, the better the growing season will be for everyone.