Biological management of apple replant disease

Project Overview

Project Type: Partnership
Funds awarded in 2014: $14,314.00
Projected End Date: 12/31/2016
Region: Northeast
State: Vermont
Project Leader:
Dr. Terence Bradshaw
University of Vermont

Annual Reports


  • Fruits: apples, general tree fruits


  • Crop Production: biological inoculants, cover crops
  • Education and Training: demonstration, on-farm/ranch research, participatory research
  • Pest Management: biological control, biorational pesticides, integrated pest management
  • Production Systems: organic agriculture
  • Soil Management: soil microbiology

    Proposal abstract:

    Apple replant disease (ARD) is a serious disorder that reduces tree growth and cumulative yield on affected trees planted on previous orchard sites. ARD is caused by a complex of soil fungi, bacteria, and nematodes that may act synergistically to cause disease. This complex is variable by orchard site and management history, so blanket management recommendations are difficult. Historically, ARD was managed with preplant soil fumigation with methyl bromide or application of broad-spectrum biocides that had significant negative environmental and human health impacts. As those materials have been phased out of use, other preplant practices, including cover crops, application of composts, and fallow periods have replaced them, with varying success. Northeast apple growers are replacing old orchards with high density modern plantings that may improve orchard profitability and sustainability. Many of these orchards are affected by ARD, and few post-plant ARD mitigation practices are available. Biopesticides are biologically-derived materials that may control pests or diseases on many crops. However, many registered materials have not been tested for efficacy on specific crops and diseases. This project will assess tree growth and crop yield improvements from two promising and commercially-available biological control materials in two ARD-affected orchards in Vermont. Cropping differences will be translated into potential opportunity costs associated with increased orchard performance.

    Project objectives from proposal:

    This project proposes to assess two commercially-available biopesticide products, alone and in combination, in two orchards planted in 2011 that exhibit ARD symptoms. Trees in both orchards that are planted on sites where apple trees were grown previously show visible reduction in growth and fruit yield compared to neighboring trees in the same planting that were planted in drive rows or other land where trees were not present in the previous planting. One site has previously shown presence of P. penetrans nematodes in a previous study, and trees planted where apple trees had been present prior to orchard establishment showed symptoms of the disease (Costante, Mai et al. 1987).

    The first orchard is located at the University of Vermont Horticulture Research Center in South Burlington, VT (HRC). The soil is a Windsor Adams loamy sand. A previous orchard was maintained on the planting site from 1990 through 2009. After removing trees in fall 2009, the site was plowed, limed, and cover cropped with sudan grass followed by oilseed mustard, which were incorporated into the soil prior to planting. Tree rows were subsoiled and preplant compost was applied at 16 tons per acre. ‘Royal Empire’ trees grafted to Bud. 9 dwarfing rootstocks were planted in 2011 in a tall spindle training system with tree density of 1210 trees per acre (3 ft x 12 ft tree spacing). Standard management practices including weed control, irrigation, and pest management sprays have been performed since orchard establishment. The second planting is located at a commercial orchard in South Hero, VT (SHVT) on Amenia and Kendall silt loam soils. The previous orchard was maintained on the site from 1900 to 2009. Trees were removed in 2009 and drainage was performed (installed) prior to replanting. In 2011, 150 trees on EMLA-26 rootstock were planted at a tree density of 350 trees per acre. Standard horticultural practices have been applied since planting.

    At each site, four treatments will be applied to five single-tree replicates per treatment in a completely randomized design. Treatments will include: 1) non-treated control; 2) MeloCon at four lbs/acre; 3) Actinovate AG at 12 oz/acre; and 4) MeloCon and Actinovate AG combined. Treatments will be applied as a soil drench within the drip line of individual trees in the equivalent of 100 gallons of water per acre. Treatments will begin at pink bud stage (roughly May 1) and will be repeated every 60 days, or roughly on July 1 and September 1, for a total of three treatments per season. Treatments will be repeated on the same trees for two growing seasons.

    Measured variables will include tree growth (trunk cross-sectional area (TCSA) at the beginning and end of each season, and vegetative shoot length and canopy size each season), fruit yield (bushels per acre equivalent), and fruit size. Additionally, soil will be analyzed for trophic diversity of nematode communities (Neher and Lee Campbell 1994) at the end of the project. This data will not only measure effects of treatments on nematode populations, including plant parasitic species, but trophic nematode indices are a measure of soil ecological condition (Freckman 1988, Bongers 1990). All data will undergo an analysis of variance (SAS Institute Inc. 2002-2004) to determine effects of experimental treatments on measured parameters. In addition, changes in fruit yield and size will be correlated to potential changes in income per acre in order to allow commercial growers to assess treatment impacts on their businesses.

    The proposed project is oriented toward supporting apple growers, and outreach materials will be geared toward that audience. Throughout the project, updates will be broadcast via existing outreach channels. These include a website (, YouTube channel ( and a grower email database that includes over 350 subscribers in Vermont and within the region. In winter 2013-2014, the UVM Apple Program is conducting a redesign of its communications platform to modernize its website and to develop social media platforms via Facebook and Twitter; these platforms will also be used to publicize the project. The UVM Apple Program is highly-regarded by regional apple growers, with 75% of growers indicating that information provided by the program was useful or very useful in their overall farm management (Bradshaw and Berkett 2013). Beginning with the 2014 growing season, responsibility for the overall operations of the program are being transferred to Terence Bradshaw, with support from USDA E-IPM grants program. However, while electronic communications are important in dissemination of information to growers, results from field trials may best be seen by observing the plantings. In summer 2015, a grower field day will be held at the HRC site (funded by E-IPM grant), where this project will be presented. Final results from the project will also be presented at regional meetings in winter 2015 (e.g. Vermont Tree Fruit Growers Association annual meeting, New England Vegetable and Fruit Meeting).

    Literature Cited

    Bongers, T. (1990). "The Maturity Index: An Ecological Measure of Environmental Disturbance Based on Nematode Species Composition." Oecologia 83(1): 14-19.


    Bradshaw, T. L. and L. P. Berkett (2013). Vermont Apple IPM Program Evaluation. unpublished.


    Costante, J., W. Mai, J. Aleong and R. Klein (1987). "Effects of apple rootstocks and nematicides on Pratylenchus penetrans populations and apple tree growth." Journal of the American Society for Horticultural Science 112.


    Freckman, D. W. (1988). "Bacterivorous nematodes and organic-matter decomposition." Agriculture, Ecosystems & Environment 24(1–3): 195-217.


    Neher, D. A. and C. Lee Campbell (1994). "Nematode communities and microbial biomass in soils with annual and perennial crops." Applied Soil Ecology 1(1): 17-28.


    SAS Institute Inc. (2002-2004). SAS 9.1. Cary, NC.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.