2019 ASHS Annual Conference

Adoption of certified organic apple production in the northeastern United States is constrained in part by frequent summer precipitation that fosters weed germination and growth, including many persistent perennial weeds. Organic growers in this region have few options for effective weed management and often cite weeds as the most constraining management barriers. While previous research studies have shown that mulch can be an effective weed control practice, organic growers currently favor cultivation or mowing, with occasional hand weeding. In an effort to improve efficacy of organic weed management tools while reducing associated time, labor, and equipment costs, researchers sought to develop a more integrated approach to organic weed management. In 2015, a NOFA-NY certified organically managed experimental orchard with ‘Honeycrisp’/‘Budovsky.9’ trees trained as a tall spindle was established at Cornell Orchards in Ithaca, New York. In 2016, a no intervention control, cultivation, and surface-applied wood chip mulch were implemented as main treatments. Sub-treatments of mowing and two organically approved herbicides were then overlaid to complete the randomized, split-plot design. The design includes eight tree rows which are divided into four complete blocks. As part of this long-term, systems-level experiment, weed cover and biomass, weed species biodiversity, soil properties, foliar nutrition, and tree growth are measured annually. Despite an overall increase in weed biomass in 2018, mulch continued to reduce weed biomass by 24% and 35% compared to control and cultivated plots, respectively. When mulch and an organic herbicide were used in the same plot, weed biomass was reduced by 67% on average compared to mulch alone. Mulch plots increased soil organic matter by 14% compared to control plots and 12% compared to cultivated plots. Similar increases were observed for soil carbon, aggregate stability, and soil respiration under mulch. While our study found that integrating mulch into organic apple orchards can reduce weed competition and improve soil health, these benefits came at the cost of tree growth – possibly due to water saturated soils under the mulch. Understanding the best management practices for weed control in organic orchards will require observations over a number of years with varying weather patterns.