2025/10/06 by Emma Volk, Glen Fox, Steven A. Fennimore +2 · 1 voice
Agricultural and Biological Sciences · #Plant Disease Management Techniques
paper · doi:10.21273/hortsci18709-25
openalex publication_date 2025/10/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Steam has been used for decades as a nonchemical alternative for soil disinfestation in stationary settings such as greenhouse crop production. However, disinfesting large soil volumes through field-scale steam applications is limited by time, labor, carbon inputs, efficacy, and economic factors. Exothermic substances added to soil before or during steam applications have the potential to improve the control of soilborne pathogens and weed propagules. To test this hypothesis, a 2-year microplot study was conducted to evaluate weed and pathogen suppression with steam in combination with two exothermic substances: quicklime and sodium peroxide. Treatments included a nontreated control, 30-minute steam application, sodium peroxide amendment, sodium peroxide amendment with 30-minute steam application, quicklime amendment, and quicklime amendment with 30-minute steam application. Steam was injected at a depth of 10.2 cm using a stationary SIOUX steam generator and steam-graded spike hoses. Pythium propagules per gram of soil were assessed via a wet plating assay. Weed suppression was assessed by evaluating germination rates of artificially introduced weed seeds (vetch, ryegrass, sida) and tubers (yellow nutsedge). Pythium propagules (ppg) significantly decreased in comparison with the nontreated control when steam was applied to quicklime-amended soil in both years at the distance of 2.5 cm from steam injection (7.4 ppg in 2021; 0 ppg in 2022) and the 12.5 cm mark from steam injection (41 ppg in 2021; 0 ppg in 2022). Only at the distance of 2.5 cm did steam alone decrease Pythium significantly (0 ppg in 2022). The sodium peroxide amendment did not improve Pythium suppression at any distance from steam injection. Similarly, weed propagules 2.5 cm from steam emitters were suppressed, and the addition of exothermic substances did not improve propagule suppression. Beyond 12.5 cm, no steam treatment affected weed propagule germination. At a distance of 12.5 cm from emitters, the addition of exothermic substances improved propagule suppression in one of two years, but the results were variable. Reduction in weed propagule emergence was highly correlated with the maximum soil temperature, and clustered distributions suggested that critical threshold temperatures are necessary for adequate suppression.