02 Oct Aphanomyces Root Rot: What Does It Mean for Your Peas?
Now that harvest is coming to a close, many growers are reflecting on this year’s crop and thinking about what went well and what didn’t. If you noticed brown roots, yellow plants or a decrease in yield, Aphanomyces Root Rot (ARR) should be the first thing on your mind. ARR is one of the most devastating diseases your pulse crops can encounter, decimating pea yields by as much as 70% in severe infestations (1). In this week’s edition of growing possibilities, we will be highlighting the need to know information every pea farmer should have about Aphanomyces and why now is the time to act.
Aphanomyces Root Rot is caused by the pathogenic mould Aphanomyces euteiches. This pathogen is present in soils across both Canada and the USA, with a large presence in Eastern Canada and more recently Alberta (1). A. eutieches is soil-borne and persists in fields as thick-walled spores (to be specific oospores) that can lay dormant in soil for up to ten years between infections (2). Excessive moisture in soil creates ideal conditions for this pathogen to infect, and when these conditions exist in a field with a susceptible crop, oospores can germinate and cause infection within minutes of reaching plant roots (1). Infection can occur at any point in the season, but most commonly occurs at seeding stage (3). After infection, symptoms can begin to show within 7-14 days and include stunted early growth, wilting, premature death, delayed maturity, reduced pod size & seed quantity, and roots taking on a honey-brown coloration (Fig. 1).
These symptoms can be vague and can resemble those of other diseases, making the correct diagnosis of Aphanomyces difficult in the field. The best way to know for sure if you have ARR in your crop is through soil testing. Post-harvest is an optimal time to start sampling. Take samples from 5 spots in your field, forming a W-shaped pattern. Field entrances and low points (depressions) are the most at-risk areas for an ARR infestation, so starting in these areas is a good idea (4).
Controlling Aphanomyces infestations is difficult, with the longevity of spores in soil diminishing the effects of crop rotations on breaking the disease cycle. Research has shown that some species of arbuscular mycorrhizal fungi as well as some species spore-forming bacteria may act as biocontrol agents. Experimental trials showed that using some species as a seed treatment alongside a fungicide can improve seedling emergence compared to use of a fungicide alone (1).
1) Wu, L., Chang, K. F., Conner, R. L., Strelkov, S., Fredua-Agyeman, R., Hwang, S. F., & Feindel, D. (2018). Aphanomyces euteiches: A Threat to Canadian Field Pea Production. Engineering, 4(4), 542–551. https://doi.org/10.1016/j.eng.2018.07.006