Effects of Occultation on Weed Pressure, Labor Costs, Product Quality, and Yield in Sustainable Vegetable Production in Northern California

Project Overview

Project Type: Professional + Producer
Funds awarded in 2019: $49,994.00
Projected End Date: 05/30/2020
Host Institution Award ID: G220-19-W7502
Grant Recipients: Community Alliance with Family Farmers; UC Davis Russell Ranch Sustainable Ag Research Facility
Region: Western
State: California
Principal Investigator:
Dave Runsten
Community Alliance with Family Farmers
Kali Feiereisel
Community Alliance With Family Farmers

Information Products


  • Vegetables: beets, carrots


  • Education and Training: on-farm/ranch research
  • Farm Business Management: labor/employment
  • Pest Management: Occultation


    Effects of Occultation on Weed Pressure, Labor Costs,  Product Quality, and Yield in Sustainable Vegetable Production in Northern California

    Organic row crop vegetable growers are overly reliant on tillage to manage weed pressure due to their inability to spray herbicides. These farms are limited in methods they can employ to control weeds. For small-scale farms that are attempting to reduce/eliminate tillage, the main method used for cultivation is hand labor which is increasingly expensive and hard to find. Recently, growers across the United States have started experimenting with a process called occultation. Occultation involves irrigating a growing area and then putting a black, 5 millimeter tarp over the top of a growing bed and leaving it there for 2-6+ weeks. Weeds in the bed germinate in warm, moist conditions, and die due to lack of light. Once the tarp is removed, the clean seed bed is planted/seeded and minimal soil disruption occurs.

    Our research question simply is, “What positive effects does occultation have on produce production?” More specifically we will measure the effect of occultation on labor hours, product quality and yield, and weed pressure in the growing area. After the results are gathered, we will co-present the research findings at two conferences (CA Small Farm Conference, Ecofarm) to at least 50 people total and create two podcasts with two of the farmers we partnered with, which will be downloaded at least 200 times total. We will write a short report on the experiment which will be published for free electronically. We will print 200 copies of the report and distribute them at conference presentations. This practice is potentially significant because with minimal up-front investment, small-scale organic farms could significantly reduce costs, improve product quality, have higher profit, implement an environmentally friendly practice, and cause less wear and tear on their bodies.

    Project objectives:

    1. Help five produce farmers in Northern California implement occultation for a four week time frame in the test and treatment plots of the research trial at their farm. (May-July 2019)  
    2. Oversee the planting, irrigation, and cultivation of the occultation treatment and control plot of five farms in northern California. (May-Sept. 2019)
    3. Manage data collection from five farms in northern California on how long they left the tarp on the occultation zone, how many labor hours went into both the control and treatment zones, and the amount of time that went into applying and removing the tarp. (May-July 2019)
    4. Measure the weed pressure and types in the occultation zone vs. the control zone at three points after tarp removal: 30%, 60% and 90% of crop maturity. (June-December 2019)
    5. Measure the produce quality of the crop in the occultation zone vs. the control zone at harvest.  (September 2019 - January 2020)
    6. Measure the yields in each of the five plots (treatment and control) at harvest. (September 2019 - January 2020)
    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.