Disease Suppressive Soils
by John Kempf, Founder of AEA
August 17, 2015
Developing disease suppressive soils is a fascinating area of research, with the potential to completely change how we manage plant diseases in the very near future. As we learn more about the factors which allow soils to suppress potential pathogens, we are better able to manage these influences in the field, and produce soils which can greatly reduce or even eliminate plant infection by a broad range of soil borne pathogenic organisms.
Disease suppressive soils are defined as “soils in which disease development is suppressed even though the pathogen is introduced in the presence of a susceptible host.” There is a spectrum of disease suppression, ranging from soils which are conducive to disease, to those which actively suppress potential pathogens and prevent them from expressing themselves as disease.
Understanding disease suppression is an important part of understanding soil/plant/microbiome interactions, and critical to developing fully regenerative agriculture systems.
Developing disease suppressive soils is an area of extensive research knowledge which we have failed to implement in production agriculture.
In 1982 the American Phytopathological Society published an 88 page booklet titled Suppressive Soils and Plant Disease. This little book was based on presentations from a symposium entitled “Nature of Soils Suppressive to Soilborne Plant Diseases” which was held in conjunction with the annual meetingof the Society in August of 1981.
The research documented in this book is absolutely fascinating, with chapters such as: The Description and Occurrence of Suppressive Soils, by Huber and Schneider; Induction of Suppressiveness, by Baker and Chet; and Use of Pathogen Suppressive soils for Disease Control, by Cook. The papers presented in this book and the cited references provide much of the foundational research work on disease suppressive soils.
This book was published thirty three years ago. What has been done since? Disease suppression is currently an area of considerable interest in both phytopathology and soil microbiology research, but very little has been done to transfer this knowledge to the field. Many of the mechanisms connected to developing disease suppression are directly connect to the integrity and the vigor of a plants microbiome, which Linda Kinkel describes so well in her article published in Phytopathology News.
There remains a lot we do not understand about disease suppression. But we understand enough. If we want to develop regenerative agriculture systems and reduce our dependency on pesticides, it is imperative that we begin implementing what we have already learned. Field experience is often where the breakthroughs emerge.
We have been able to develop disease suppressive soils with a variety of crops and soils types that had previously been disease conducive, sometime facilitating a transition to active disease suppression in as little as year. In particular, diseases which have been quite responsive are verticillium, fusarium, and rhizoctonia.
Developing a healthy and aggressive microbial community in the plant microbiome is a foundational element of developing disease suppressive soils. Our best field experiences have been the result of using a combination of diverse bacterial and fungal inoculants and biostimulants to drive microbial development.