Apple replant disease (ARD) is a disorder caused by biotic and abiotic factors that reduces tree growth and crop yield on apples when planted on sites that recently were planted to previously existing orchards. ARD has previously been managed with soil fumigation, but environmental concerns and losses in registration of fumigant products has changed current management practices. Recommendation for mitigation of ARD include keeping orchard land fallow for 3-5 years before replanting, use of nematode-suppressive cover crops, and more recently, the use of ARD-tolerant rootstocks. However, few post-planting management practices exist for orchards that are replanted on ARD sites to susceptible rootstocks. In this project, two organically-acceptable biopesticide products were evaluated to determine effects on tree growth and crop yield on two sites in 2014 and 2015. Neither product, Actinovate AG nor MeloCon, were statistically significantly effective in improving most measured parameters (terminal shoot growth, number of fruit per tree, or total; kg crop harvested in either year) although increases in tree growth were observed at one site for the Actinovate treatment. This lack of tree growth and apple yield difference drove the same result in an economic analysis of each treatment with ~$800/acre in material costs. Thus no product produced a positive return. Major plant parasitic nematode levels in the soil (indiviual #s per gram of soil) were not statistically different among the treatments.
Results from this project were presented to grower stakeholders in presentations at the 2015 and 2016 Vermont Tree Fruit Growers Association/UVM Apple Program Annual meetings. Results from the project were also presented in January, 2016 at a scientific forum via a poster presentation and discussion at the Northeast Plant, Pests, and Soils Conference in Philadelphia, PA. A complete publication on project results is in preparation for submission to the journal HortTechnology.
Apples are an important component of the agricultural economy in the northeast, where over 14,000 acres of orchards generate approximately $66 million in farmgate receipts annually . In Vermont, orchards contribute nearly $20 million to the local economy, and are the second-most important specialty food crop, after maple . However, apple production systems are not static, and orchards have seen significant changes in varieties and planting systems over the past several decades. Orchards are increasingly being planted to smaller trees on dwarfing rootstocks and higher tree densities per acre, with increased up-front establishment costs over traditional, lower-density plantings . Increased planting costs are offset by increased precocity and greater yield at maturity, but management problems during early orchard establishment may reduce overall profitability of these systems . Apple replant disease (ARD) is a disorder caused by a complex of fungal, bacterial, and nematode pathogens that affect tree fruit crops when planted on sites where those crops were previously . In past years, ARD was managed with preplant soil fumigation with methyl bromide or treatment with organophosphate biocides , but those materials have been or are being phased out due to environmental concerns. Presently recommended practices to mitigate ARD in new orchards include preplant cover copping, multi-year fallow periods, and use of resistant rootstocks , but those practices are not always effective in supporting optimum tree growth . In many cases, growers are planting new orchards on previous orchard sites without adequate ARD mitigation because they cannot afford multiple years of lost production during mitigation, and resistant rootstocks are not as commercially available as more common dwarfing rootstocks . Few post-plant ARD treatments are available to growers, and some treatments that are available are inadequately tested on orchard crops. As a result, local growers are investing in modern plantings that are being affected by ARD, which compromises overall profitability of the orchard, and may jeopardize long-term sustainability of the industry in the region.
Fruit growers, who may be good stewards of the land with interests in overall orchard, and maybe even soil, ecology, are primarily interested in attaining optimum tree growth and fruit yield in their plantings in order to optimize profitability. Given the limitations in funding for this program, and the focus on farm-level impacts that improve productivity and increase farm income; conserve soil and improve water quality; reduce environmental and health risks; prevent agricultural pollution; and improve the quality of life for farmers, this project proposes to assess horticultural impacts on tree growth and fruit yield from application of two biopesticide products in two ARD-affected orchards in Vermont. By completing this research, effective mitigation tactics for ARD-affected orchards in New England may be identified to assist growers in managing this disorder.
Management of ARD with biologically derived materials (biopesticides) is a relatively new practice. However, causative agents of ARD vary by orchard location, so specific biopesticide materials may vary in efficacy for any given orchard . ARD is associated with microbial pathogens and nematodes which may combine synergistically to increase disease incidence . Because of this, many biopesticide materials have been trialed in laboratory and orchard conditions with varying results. Streptomyces lydicus WYEC 108 has shown strong antagonism against soilborne Pythium and Rhizoctonia spp. which was attributed to production of extracellular antifungal metabolites . S. lydicus is also reported to produce chitinase compounds that reduce viability of some soil plathogens . Another biopesticide agent, Paecilomyces lilacinus, has shown efficacy in managing diseases caused by plant parasitic nematodes in multiple crops [13-15]. Studies of the effectiveness of commercially available biopesticides in improving tree growth or fruit yield on apple replant sites are lacking, and no such studies were found in a review of the literature.
Two commercially available products have recently been released in the U.S. that are labeled for use on apple to manage soil pathogens implicated in ARD . MeloCon® WDG (Certis USA LLC, Columbia, MD) is a biological nematicide with the active ingredient P. lilacinus. MeloCon is labeled for use as a soil drench in many fruit and vegetable crops, including apple. Product claims include broad activity against 19 genera of plant-parasitic nematodes and a soil half-life of roughly one month. Actinovate AG (Natural Industries, Inc., Houston, TX) is a biological fungicide containing S. lydicus WYEC 108, and is labeled for use as a foliar spray and soil drench to manage many fungal diseases on multiple crops. Manufacturer use recommendations for apples include use as a soil drench to prevent disease incidence from Pythium, Phytophthora, Fusarium, Rhizoctonia and other root rot fungi . Because ARD is caused by complex and interacting soil microbes, multiple biopesticide strategies may be more effective than single-use materials in managing the disease . This project assessed two commercially-available biopesticide products 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 showed 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 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 .
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The objective of this study is to evaluate improvement in tree growth, crop yield, and fruit weight in two Vermont apple orchards affected by ARD. Because effects of management on soil biological communities occur over several months to several years, and changes in tree productivity may take longer to assess, this project was proposed to occur over two seasons with the same treatments applied to the same trees in order to assess long-term cumulative effects. We hypothesized that improvements in tree growth and orchard productivity will be seen after two years of biopesticide application.
The first orchard is located at the University of Vermont Horticulture Research & Education Center in South Burlington, VT (HREC). 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 in 2010 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 to the tree row strips at 16 tons per acre. ‘Royal Empire’ trees grafted to Budagovsky 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). 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 tile drainage was installed prior to replanting, but no significant ARD mitigation procedures were performed except for leaving the site fallow during preparation. In 2011, 150 ‘McIntosh’ trees on semidwarf EMLA-26 rootstock were planted at a tree density of 345 trees per acre (9 ft x 14 ft tree spacing). Standard management practices including weed control (mowing and/or herbicide strips), irrigation, and pest management sprays have been performed at both sites since orchard establishment.
At each site, three treatments were applied to five replicates per treatment in a completely randomized design. At HREC five-tree replicates and at SHVT two-tree replicates were used. Treatments included: 1) non-treated (water) control; 2) MeloCon at four lbs/acre/treatment; and 3) Actinovate AG at 12 oz/acre/treatment. Treatments were applied as a soil injection with Rears Pak-Tank Sprayer (Rears Mfg Co., Eugene, OR) and OESCO FN-12 Root Feeding Needle (OESCO, Inc., Conway, MA) within the drip line of individual trees in the equivalent of 192 and 164 gallons of water per acre at 100 psi at HREC and SHVT, respectively. A wetting agent (ThermX 70, American Extracts, Strathmore, CA) was included in each application at manufacturer-recommended rates to improve penetration of the material into the root zone.
At each site, three treatments were applied to five replicates per treatment in a completely randomized design. At HREC five-tree replicates and at SHVT two-tree replicates were used. Treatments included: 1) non-treated (water) control (NTC); 2) Actinovate AG at 12 oz/acre (ACT); and 3) MeloCon at four lbs/acre (MCN). Treatments were applied as a soil injection with Rears Pak-Tank Sprayer (Rears Mfg Co., Eugene, OR) and OESCO FN-12 Root Feeding Needle (OESCO, Inc., Conway, MA) within the drip line of individual trees in the equivalent of 192 and 164 gallons of water per acre at 100 psi at HREC and SHVT, respectively. A wetting agent (ThermX 70, American Extracts, Strathmore, CA) was included in each application at manufacturer-recommended rates to improve penetration of the material into the root zone. Treatments occurred on four dates for each site in 2015 and 2015 (Table 1).
Measured variables included tree growth (trunk cross-sectional area (TCSA), vegetative shoot length, and terminal leader length), fruit yield (kg/tree), fruit number per tree, and fruit size (g/fruit, calculated from fruit number and kg yield). Soil cores were collected in each treatment-replicate at both sites on July 29, 2014 and July 30, 2015 and analyzed for trophic diversity of nematode communities by identifying to genus in the UVM Soil Bioindicators Laboratory . Soil nematode community analysis was completed at the same time each season in order to minimize temporal variation in nematode communities, thus, analysis was not conducted at the beginning nor end of the total project. This data not only measured effects of treatments on nematode populations, including plant parasitic species, but trophic nematode indices are a measure of soil ecological condition [21, 22].
All data were subject to an analysis of variance  to determine effects of experimental treatments on measured parameters. If the overall F-test for was significant at α=0.05, then multiple comparisons were made with Tukey’s adjustment applied to minimize type II error.
Tom Weicht collecting soil samples at Hackett’s Orchard for nematode community analysis in SARE Apple Replant Disease Project.
Molly Klepack harvests fruit from SARE ARD research orchard. Brassicas like canola are a commonly-grown cover crop to mitigate ARD, but they are not effective to use after an orchard has been planted.
Dr. Terence Bradshaw applies biopesticide treatments via soil injection.
- Neher, D.A. and C. Lee Campbell, Nematode communities and microbial biomass in soils with annual and perennial crops. Applied Soil Ecology, 1994. 1(1): p. 17-28.
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- Bongers, T., The Maturity Index: An Ecological Measure of Environmental Disturbance Based on Nematode Species Composition. Oecologia, 1990. 83(1): p. 14-19.
- SAS Institute Inc., SAS 9.3. 2002-2010: Cary, NC.
While observed differences were few, there appear to be some effects from biopesticide treatments on assessed parameters, but only at HREC site. Assessed tree growth and crop yield parameters are presented in Table 2. In both years, the ACT treatment had greater tree growth TCSA than the NTC, and MCN was different from neither other treatment. In 2014, the ACT treatment had the greatest leader growth (23.2 cm), followed by MCN (19.6 cm) and NTC (11.2 cm). At SHVT in 2014 the NTC treatment had greater leader growth of 41.0 cm than both biopesticide treatments (31.9-31.7. cm), but leader growth in 2015 was 1/3 or less than the previous year for all treatments, and NTC had the lowest growth. No differences in tree height were observed at the end of the project, but ACT treatment had greater tree width than NTC. There was no statistical separation among treatments for terminal shoot growth, number of fruit per tree, or total; kg crop harvested in either year.
Total nematode communities were enumerated and identified to genus in both years (Table 3). Significant differences exist in total numbers per gram dry soil between the two sites. In 2014, HREC had 61 individuals per gram versus 16 individuals per gram at the SHVT. It should be noted that the value for HREC is particularly high. Extremely wet weather in mid-summer of 2015 likely reduced total nematode populations at both sites; HREC had 16 individuals per gram of soil vs. 13 individuals per gram at SHVT. The differences between the sites are most likely due to soil texture and management where the HREC soil was sandier and cultivated whereas the SHVT was heavier and the orchard floor was mowed mix of grasses and legumes. In total from both sites 16 genera of plant parasites were identified. The two most important plant parasites were Lesion and Root Knot nematodes, both are endoparasites. Three genera, Hirshmanniella, Pratylenchoides and Pratylenchus, belong to the family Pratylenchidae (Lesion Nematode) with similar endoparasitic habits and combined for analysis. Meloidogyne (Root Knot Nematode) was also present at both sites, but less wide spread in distribution. The Coefficient of Variation (CV) was generally high. For the Pratylenchidae, the CV was typically greater than 0.7 across each treatment at both sites and for Meloidogyne, the CV was >1. Statistically, there were no significant differences for either Pratylenchidae or Meloidogyne at either site in both years. However, the SHVT site did show a trend toward reduced numbers of Pratylenchidae in the MCN treatment and a similar trend was observed in the relative proportion of Meloidogyne in the community. At HREC, ACT treatment showed a trend toward reduced populations of Meloidogyne.
Lack of any quantifiable differences in plant performance or crop yield at SHVT coupled with very low yield in 2015 suggests that this orchard may suffer from other, non-biological causes of ARD. It is surmised that this orchard has low levels of mineral nutrients in the soil because foliar nutrient values were low for all mineral evaluated (data not shown) and the host grower did not fertilize the trees in this study. Improved management of soil and foliar nutrition may increase performance of these trees, and may improve efficacy of biopesticide treatments applied to manage ARD symptoms.
A lack of quantifiable results overall indicates that the products evaluated are not likely to affect tree growth or crop yield when used at the rates and via the application methods used in this study. However, negative results do not indicate a failure of the study. Many products available to growers to use as biological growth promoters or stimulants have been little-studied and reported in the scientific literature, and their thorough evaluation may prevent growers from spending money on products or methods that yield few results. In addition, growers reported increases in knowledge about ARD in general (referenced below under ‘Farmer Adoption’), which may translate into improved pre-plant management which will result in increased future orchard performance.
Education & Outreach Activities and Participation Summary
Results from this project were presented to grower stakeholders in presentations at the 2015 and 2016 Vermont Tree Fruit Growers Association/UVM Apple Program Annual meetings attended each year by 65-70 growers [24, 25]. In addition, interested stakeholders have been referred to progress reports located at Northeast SARE website. Results from the project were also presented in January, 2016 at a scientific forum via a poster presentation and discussion at the Northeast Plant, Pests, and Soils Conference in Philadelphia, PA attended by over 300 scientists, extension educators, and graduate students from multiple disciplines . A complete publication on project results is in preparation for submission to the journal HortTechnology.
25. Bradshaw, T. 2014 Apple Season Roundup. 119th Annual Vermont Tree Fruit Growers Association & UVM Apple Program Annual Meeting. 2/12/2015. http://www.uvm.edu/~fruit/treefruit/tf_meetings/BradshawVTFGA15.pdf
26. Bradshaw, T. Apple Replant Disease. UVM Apple Program & VT Tree Fruit Growers Assn 120th Annual Meeting. Middlebury, VT. 2/18/2016. http://www.uvm.edu/~fruit/treefruit/tf_meetings/16ARDpresentation.pdf
24. Bradshaw, T., Weicht, T., & Foster, J. 2016. Biological Management of Apple Replant Disease. In A. Gover (Ed.). Proceedings of Northeast Plants, Pests, and Soils Conference. 1:64. Philadelphia, PA. 1/6/2016.
An economic analysis of the use of the studied biopesticides was conducted (Table 4), but given the lack of observed response on important tree growth and especially crop yield variables, no product produced a positive return at either site. Each product cost ~$800 per acre in material costs, not including the cost of application. We assumed a price of $20 per bushel for harvested fruit times in the analysis and multiplied by the the total cumulative crop yield across both years less material costs to calculate net return in $US per acre. Yield was relatively low in both orchards, and was negligible in SHVT in 2015. In the latter case, extremely low yield did not cover ARD material costs, nor were typical management costs accounted for in either orchard. In this study, neither material could be recommended at the rates or with the application method used in light of reduced economic performance in both orchards.
An informal poll of Vermont apple growers at stakeholder meetings in 2015 and 2016 indicated that none had adopted post-plant applications of biopesticides in poorly-performing orchards, which was expected given the limited and variable results. However, an evaluation of grower knowledge at the 2016 meeting indicated that 31% of growers had no knowledge of ARD prior to the presentation, 42% had minimal knowledge, and 27% had moderate knowledge (none indicated ‘considerable’ knowledge). Those same growers polled after the meeting indicated that 79% had moderate knowledge of ARD and 21% considerable knowledge. Open comments in the evaluation included: “cover crops = nice; may try mustards for apple replant” (mustard cover crops are an effective preplant cover crop to mitigate ARD); “replant disease presentation great and appropriate as many are replanting orchards”.
Areas needing additional study
The combination of increased tree growth and a trend toward reduced Meliodogyne populations in ACT treatment at one site suggests that this product may mitigate apple replant disease, but further study including rates, timing, and increased numbers of soil types is warranted. The products evaluated may provide some mitigation of ARD when applied differently, including in pre-plant treatments, through fertigation systems, or using other application techniques.