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California, Arizona Extension scientists have been studying its use.

Todd Fitchette, Associate Editor

March 11, 2024

2 Min Read
Steam injection machine
A prototype steam injection machine developed by researchers with the universities of Arizona and California shows promise for killing weed seeds and soilborne pathogens in fields planted to spinach. Other machines are planned for strawberries as scientists seek ways to control weeds and soil diseases without costly chemicals.Todd Fitchette

What once powered massive locomotives could soon help farmers control weeds and soilborne pathogens.

For several years now, Steve Fennimore, an Extension weed scientist with the University of California, and Mark Siemens, an ag mechanization Extension specialist with the University of Arizona, have teamed up on a prototype steam applicator that injects steam in the soil to kill weed seeds. Fennimore says steam is also helpful in controlling soilborne pathogens.

“The concept behind this is simple: we inject steam and kill weed seeds and pathogens,” Fennimore said.

Work for the prototype was funded by the propane council. It works on a simple process of injecting steam several inches into the soil to raise the temperature sufficiently to kill the targeted seeds and pests, without sterilizing the soil.

“I call it the Goldilocks concept: it’s not too hot or not too cold,” Fennimore said.

“People often say that we’re sterilizing the soil,” he continued. “We’re not sterilizing it. That means we’re killing everything there, leaving us with nothing but an inorganic bunch of dirt.”

Studies have shown that heating the soil to 140 degrees for over 20 minutes at a depth of two inches effectively kills 89% of the weed seeds ahead of planting. Further studies show the process reduced hand weeding times by over 80%.

Recent trials of the prototype machine confirmed these results.

Aside from crops like spinach, where mechanical weeding is prohibitive because of how densely the crop is planted, the technology shows promise for certified organic operations, where there are no useful soil fumigants.

Fennimore calls the superheated steam created a “dry steam,” which when injected disperses better. The ability of the dry steam to disperse mimics the dispersal of Methyl Bromide, which regulators are phasing out as an agricultural fumigant.

“This shows big promise for organic produce. They don’t have any good options,” he continued.

The machine on display at the Southwest Ag Summit in Yuma in February is the first design of technology that was demonstrated earlier at the University of Arizona’s Extension farm in Yuma.

“I’m anxious to work with some engineers to come up with a better design on this,” Fennimore said.

About the Author(s)

Todd Fitchette

Associate Editor, Western Farm Press

Todd Fitchette, associate editor with Western Farm Press, spent much of his journalism career covering agriculture in California and the western United States. Aside from reporting about issues related to farm production, environmental regulations and legislative matters, he has extensive experience covering the dairy industry, western water issues and politics. His journalistic experience includes local daily and weekly newspapers, where he was recognized early in his career as an award-winning news photographer.

Fitchette is US Army veteran and a graduate of California State University, Chico. 

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