Comparing Alternative Weed Management Practices to Black Plastic in CBD Hemp Production

Project Overview

Project Type: Partnership
Funds awarded in 2020: $29,993.00
Projected End Date: 11/30/2022
Grant Recipient: University of Maine Cooperative Extension
Region: Northeast
State: Maine
Project Leader:
Dr. John Jemison, Jr.
University of Maine Cooperative Extension


  • Agronomic: hemp, oats, rye


  • Crop Production: cover crops, cropping systems
  • Education and Training: demonstration, extension
  • Pest Management: cultivation, mulches - general, mulches - killed, mulches - living, mulching - plastic, physical control
  • Soil Management: green manures

    Proposal abstract:

    After an eight-decade hiatus, hemp production is back.  Farm diversity and profits can be increased if production costs can be controlled.  Approximately 2625 acres have been grown in Maine since 2017.  Hemp grown in the northeastern United States for cannabidiol (CBD)-rich flowers must be produced on wide (5x5) spacing to reduce disease due to high humidity.  No herbicides are labeled for hemp, and with the wide spacing, there is little crop shading to slow weed growth without using plastic mulch.  More than 19,000 ft2 of plastic is landfilled each year per acre of hemp produced. This waste and the fuel required to till and prepare hemp beds is unsustainable.  Planting hemp into no-tilled mowed or rolled/crimped cereal rye cover crops could reduce weed pressure and reduce cost.  Winter rye protects the soil from erosion, transpires water to dry soils in the spring, feeds microbes through root exudates, and inhibits weeds when rolled or mowed into a mulch.  In this 2-year, 2-location project, Sarah Hewitt of Victory Hemp Farm and I will evaluate CBD hemp performance in a no-till rolled/crimped or mowed rye mulch and assess possible allelopathy or nitrogen immobilization issues.  We will also evaluate novel stacked cultivation tools to see if intensive cultivation can reduce weed pressure. These systems will be compared to a tilled, standard black plastic mulch production system.  We will assess plant growth/development, flower and total plant yield, weed biomass, and cannabinoid content.  Results will be shared at grower meetings and on a hemp production website.  

    Project objectives from proposal:

    Through replicated research trials, we seek to explore novel means to manage weeds in CBD hemp production.  We will compare a standard black plastic mulch (control treatment) to rolled/crimped winter rye, sickle-bar mowed winter rye, and stacked cultivation tools.  This will be done in two experiments: one conducted with Sarah Hewitt of Victory Hemp (VHF) in Union Maine, and the other at the University of Maine Whitter Center Rogers farm (UMRF). 


    The project seeks to assess the effect of: 1) tillage on CBD hemp growth and development; 2) allelochemicals and nitrogen immobilization slowing plant growth and development; 3) rye cover crop destruction method (roller crimper or mowing) on continuity and thickness of cereal rye mat; 4) weed management treatments on weed density by species; and 5) weed density and plant stress on THC and CBD levels in the plant.  Study results will benefit farmers by providing them with research-based information on the risks and benefits of managing weeds with rye cover crops, reducing tillage, and the effects of plant stress on the total cannabinoid content in CBD hemp. 

    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.