Lentils Peas Disease Root Rot
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Adapted from article by Bruce Barker, P.Ag.

Surveys across Western Canada have found two main pathogens responsible for root rots in pulses. Fusarium species are distributed widely, with F. avenaceum and F. solani the most virulent types of root rot that can cause yield loss. Aphanomyces euteiches, first reported in Saskatchewan in 2012, is a more recent concern.

Aphanomyces root rot is most common under good soil moisture conditions. The pathogen is a water mould that depends on moisture for the zoospores to move in the soil and infect plant roots. Infection can happen anytime during the growing season, and spores can persist for many years in the soil. Root rots may still show up in drier growing conditions, and may or not be Aphanomyces root rot. 

The seedling stage seems to be the most susceptible for Fusarium root rot, but symptoms do not typically become visible until late flower. In drier years, root rot symptoms showing up later in the season may be caused by one of many different pathogens.

Aphanomyces root rot is very difficult to identify and isolate with conventional methods, and requires a DNA test for confirmation.  For fields with a history of root rot, recommendations are for growers to test their fields for the presence of A. euteiches so that they can implement practices to manage the disease if is present.

Several labs in Western Canada can test for the Aphanomyces root rot pathogen. These labs may analyze either root tissue or a soil sample.

While each lab has its own sampling and submission protocol, the following are general recommendations for soil and plant sampling: Soil analysis can be performed as a direct soil extraction or as a bait test. A soil bait test, offered by a number of commercial labs, utilizes germinating seedlings of an Aphanomyces host crop that are planted into the soil sample to induce Aphanomyces oospore germination. This test mention has been shown to provide the most consistent results when testing soil for Aphanomyces risk potential.


Plant Tissue

Some labs provide their own sample kit. Contact the lab for their specific sampling and submission requirements.

What The Results Mean

Figure 1. Healthy seedlings (left) vs root rot infected seedlings(right).

The results from a lab test in the fall can mean several things depending on the reporting lab. The first is positive or negative. This simply means that the pathogen is present in the sample, but does not put a number on the amount of spores per gram of soil, or level of infection of the root tissue. 

Some labs take the positive/negative test one step further in their reporting, where a positive result means that the pathogen is present at levels that would be capable of causing disease. A negative result cannot guarantee that the pathogen is not present in the field, but just not present in the soil sample. 

Finally, some labs provide a quantitative result reporting on the number of spores per gram of soil or levels of risk for root rots. Research by Agriculture and Agri-Food Canada has suggested higher risk for A. euteiches  in fields when levels are above 100 oospores per gram of soil in the Dark Brown soils, and 750 oospores per gram in the Brown and Black soils. However, the presence of Fusarium spp., particularly in the Brown soils, increases disease severity. Because Fusarium spp. are so widespread on the Prairies, the risk threshold for A. euteiches has been adjusted. The number of A. euteiches oospores where the pathogen may start to cause an impact on the crop has been set at 100 oospores per gram of soil for all soil types. 

If A. euteiches is confirmed in a field, growers should follow recommended management practices that include rotating to non-susceptible crops or more tolerant pulse crops such as faba beans, chickpeas, or soybeans, and maintaining a minimum of six to eight years between susceptible hosts such as peas, lentils, and alfalfa.

Labs Offering Soil and/or Plant Specimen Analysis for Root Rot Pathogens

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