Solarization and steam heat combined to control weeds in straberry

2008 Annual Report for GW08-018

Project Type: Graduate Student
Funds awarded in 2008: $19,974.00
Projected End Date: 12/31/2009
Grant Recipient: University of California, Davis
Region: Western
State: California
Graduate Student:
Principal Investigator:
Steve Fennimore
University of California, Davis

Solarization and steam heat combined to control weeds in straberry


Soil solarization performance in coastal areas of California is often inconsistent due to fog and cool summer temperatures that do not allow soil to reach high temperatures required to reliably kill soil pests. The objective of this study was to develop an economically feasible combined solarization and steam heat, soil disinfestation system for strawberry. Field studies were conducted at Salinas, CA in 2007-08 and at Camarillo, Salinas and Watsonville in fall of 2008 for the 2008-2009 seasons. Strawberry production, results show that steam treatments with and without solarization controlled weeds equal to or better than methyl bromide.

Objectives/Performance Targets

  1. 1. Evaluate the combination of solarization and steam disinfestation to control weeds and soil pests. 2. Evaluate crop yield and quality, resulting from soil disinfestation with heat from solarization and steam, compared to methyl bromide fumigation. 3. Demonstrate the solarization/steam soil disinfestation technique to growers. 4. Conduct economic analysis of solarization/steam disinfestation to determine if it is commercially viable.


During August to November of 2008, field trials and demonstrations were conducted at Camarillo, Salinas and Watsonville. The Salinas trial at the Spence research farm tested the combination of steam and solarization. In 2008 field trials, two new technologies were tested to apply steam to the soil; polyethylene pipes buried 20.3cm below the surface and SynTex steam hose with steel spikes that were installed on the bed tops and injected steam into the soil through the spikes. Testing both of these techniques worked toward our goal, to find the most effective and energy efficient steaming method.

Results from both 2007 and 2008 field trials have shown steam alone and combined with solarization was equal to or better than fumigation by methyl bromide in controlling weeds. Verticillium dahliae is a major soil pest of strawberry growers. To test different treatments in controlling V. dahliae mesh bags of soil infected with V. dahliae were installed within plots at different depths prior to treatments. Later these samples were dug up and assayed in a laboratory to determine microsclerotia viability. Viability assays of V. dahliae microsclerotia showed no statistical difference between fumigation with methyl bromide and the pipe steam treatments. Solarization alone was not enough to control V. dahliae as it was not statistically different from the control. These results for both weeds and Verticillium demonstrate steams abilities to disinfect soil.
Two huge milestones occurred when we steamed a field of 183m for the Reiter Associates, Watsonville, CA and 100m at Camarillo, CA. This demonstrated that steaming of a larger area was not only possible but could be accomplished using the same equipment we use for smaller plots.

Impacts and Contributions/Outcomes

In 2008, Dr. Fennimore gave three extension talks on the use of steam, at which both researcher and growers attended. In February 2008 Celeste Gilbert gave a talk at the California Weed Science Society annual conference in Monterey CA., at which both growers and scientists were in attendance. In June of 2008, our lab participated in the strawberry field day at the Spence Research farm at Salinas, CA. During the field day Ben Weber performed demonstrations of applying steam in the field to those who attended.
Interest in the use of steam by California organic growers increased when it was deemed that steam could be used as a pest management tool within organic production. In 2008, two organic growers (one strawberry and one raspberry) commissioned the lab to treat their fields with steam, thereby allowing us to demonstrate the disinfestation technique to growers within their own fields.