Soil solarization as a tool to control weeds and soilborne pathogens in tree seedling nurseries in the Pacific Northwest

Project Overview

Project Type: Research and Education
Funds awarded in 2016: $247,329.00
Projected End Date: 11/30/2019
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Principal Investigator:
Dr. Jennifer Parke
Oregon State University


  • Additional Plants: ornamentals, trees


  • Education and Training: demonstration, extension, on-farm/ranch research
  • Pest Management: soil solarization
  • Soil Management: soil microbiology, soil physics
  • Sustainable Communities: sustainability measures


    The purpose of the research is to determine if soil solarization under Pacific Northwest conditions is a feasible strategy for managing weeds and soilborne pathogens in tree seedling nurseries. We conducted replicated on-farm trials to test the efficacy of soil solarization in commercial tree seedling nurseries in Mima, WA; Boring, OR; and Yamhill, OR. We also conducted a replicated field experiment to examine how soil moisture and solarization duration affect solarization effectiveness. We examined soil solarization effects on viability and germination of four weed species, quantified fall emergence of naturally occurring weeds, measured impacts on populations of soilborne Fusarium and Pythium spp., examined effects on soil microbial communities, and monitored soil temperature, soil moisture, and local weather during the experiments. We demonstrated that soil solarization resulted in crop growth benefits and reduced the time needed for hand weeding by 52-54%. We produced an initial version of an online soil solarization model to help growers forecast the effectiveness and minimum time required to achieve effective soil solarization based on their location and start date. Other outreach activities included four talks to Pacific Northwest grower groups, a field day, a grower workshop, publications in two grower magazines, and thirteen presentations at regional or national scientific conferences.

    Project objectives:

    1. Determine if soil solarization is an effective and economically feasible way to control weeds, soilborne plant pathogens and improve tree seedling growth in Pacific Northwest nurseries.
    2. Optimize soil solarization for Pacific Northwest conditions. Determine optimal solarization duration by evaluating the effect of soil moisture conditions and soil texture on achieved soil temperature.
    3. Develop a web-based grower-friendly model for predicting the length of time necessary for disinfesting bareroot nursery soil based on geographic location, soil moisture content, and start date. 
    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.