Soil Ecology Research Laboratory

Preplant soil compost and fumigation, rootstock disease resistance, and soil microbial species diversity as factors in apple replant disease

Project summary:

Fruit growers renovate and replant orchards periodically to maintain productivity and exploit market opportunities for new varieties. Performance and profitability of replanted apple orchards are often threatened by a soil-borne disease complex known as apple replant disease (ARD). ARD has complex and variable causes in different regions and soil types. In the past, broad-spectrum soil fumigants such as methyl bromide provided the most effective control of ARD, but methyl bromide is being phased out and more sustainable ARD controls are needed. This project explores four alternatives to methyl bromide-diseaseresistant apple rootstocks, soil treatments with compost, use of an alternative soil fumigant (Telone C-17), and replanting outside of previous tree-row locations-in a commercial orchard with a history of ARD. We will also investigate potential mechanisms of disease suppression, including changes in soil microbial diversity and dominance, and patterns of apple root growth and survival for six clonal rootstock genotypes following different preplant soil treatments. We will evaluate tree growth, nutrient uptake and yield, microbial species composition in the rhizosphere, root growth phenology and survivorship, and the cost/benefit ratios for each treatment factor during the next several years. The results from this and previous related research will be integrated into a comprehensive program of extension demonstrations and publications to help Northeastern fruit growers manage orchard replant problems.

Objectives:

1. 1. To evaluate the resistance or tolerance of diverse apple rootstock genotypes to apple replant disease (ARD) syndrome in an orchard site.
   2. To compare soil fumigation with compost soil amendments as preplant treatments for suppressing ARD and promoting successful tree establishment and yields.
   3. To observe and compare root phenology, root morphology, and survival of six rootstocks in soil following various preplant treatments.
   4. To investigate soil bacteria and fungal species diversity, dominance and community structure in the rhizospere following preplant compost and soil fumigation treatments to further understand the promulgation of the disease state in ARD, the devlopment of disease suppressive microbial communitites by use of compost and the effects of fumigation on soil microbial community dynamics.
   5. To conduct educational programs and devlop and comprehensive extension publication for growers confronting orchard problems in the Northeast U.S.
   

Project staff:

Principal Investigator: Ian A. Merwin, Cornell University, Horticulture
Co-Investigator: Eric B. Nelson, Cornell University, Plant Pathology
Co-Investigator: Janice E. Thies, Cornell Universiyt