Integrated Approaches Are Needed To Manage Weeds in Organic Apple Orchards

Abstract

Prolific weed growth during rainy, humid summers coupled with poor efficacy of available weed management strategies remains a major barrier to adoption of organic apple production in New York. The effects of multiple, in-row weed management strategies on weed cover and biomass, soil health, and tree growth and productivity were assessed via a split-plot experiment implemented in 2016 in a certified organic apple orchard in Ithaca, NY, USA. Main treatments included cultivation with a Wonder Weeder (cultivation), surface-applied wood chip mulch (mulch), and an untreated control (main). Split treatments included ammoniated soap of fatty acids (ammoniated soap), capric/caprylic acid (capric acid), mowing with a string trimmer (mowing), and an untreated control (split). The mulch was applied once, in Spring 2016; all other treatment combinations occurred four times per season, about monthly from May to August. Between 2017 and 2019, nearly all measured soil health parameters increased under the mulch treatment relative to the control (main) treatment. Notably, soil organic matter in the mulch treatment increased from 4.8% in 2016 to 5.2% in 2019 but declined in the cultivation treatment from 4.5% to 4.1% during those years. Regardless of the split treatment, the mulch treatment maintained 16% to 45% less weed biomass than the other main treatments throughout the study. The split treatments became a more significant factor in the latter years. Regardless of the main treatment, the split treatments of ammoniated soap, capric acid, and mowing all maintained less than 200 g·m-2 of weed biomass per sampling period, which was significantly less than the control (split) at sample dates 3 and 4 in 2017 and sample dates 2 to 4 in 2018 and 2019. This was mainly due to an abundance of Symphytotrichum lanceolatum and Solidago spp. in main treatment combinations with the control (split) treatment. Tree growth was greatest in the cultivation treatment, in which trunk cross-sectional area quadrupled between Spring 2016 and Fall 2019. These findings demonstrate that multiple approaches are needed to obtain adequate weed control and balance orchard productivity and soil health during the establishment period of an organic apple orchard in New York.