Soils, Mulches and Organic Amendments

The Role of Tillage on Pathogen Survival and Seedling Establishment in a Clay Soil

Researchers: James Downer, UCCE-VC & Howard Ferris, UCDavis.

Soil-borne root damaging diseases often result as a consequence of cropping the same kinds of plants on the same land over a number of years. Pathogenic propagules such as hyphae, sclerotia, microsclerotia, chalmydospores, and oospores of various root rot fungi increase in quantity until they overwhelm the biological or other systems that keep them in control. Land at the Hansen Agricultural Center has such pathogens in the pumpkin patch area and are well suited to study. Simple crop rotation can avoid disease; however, many pathogens survive for years in soils and thus soils can become unusable for some cropping situations. Hi dollar crops such as berries, specialty vegetables and ornamental color plants in landscapes have relied on fumigants and fungicides to return these soils to productivity. Unfortunately, fungicidal options are often not available to organic growers or to many landscapers where pesticide uses are limited. Fumigants are also in imminent threat of loss of registration in California for many uses. Development of a sustainable “healthy” soil that is repressive to soil-borne pathogens is a goal for every grower and gardener weather or not they consider their production methods “organic”.

           Composts are associated with disease control in a number of plant-disease systems such as damping off disease of radish and Phytophthora diseases in vegetables and woody plants.  Composts are stabile organics that have a direct impact on soil mineral content and can provide microbes necessary to control pathogens. However, incorporation of compost (tillage) itself also changes the biology of soils. A long-term study at HAC (funded last year for further soil analysis) provides preliminary evidence that tillage alone can increase soil suppression of Phytophthora, change the structure and function of the soil food web (as evidenced by nematode populations).