Methyl Isothiocyanate Concentration, Distribution, and Persistence in Sandy Soil as Influenced by Dazomet Post-application Practices

Dazomet is a fumigant commonly used to control soil seedbanks and plant tissues of weed species in highly infested turfgrass areas. This fumigant reacts with water in the soil when in the presence of oxygen and releases methyl isothiocyanate (MITC) gas that kills seeds and plant tissues within the soil. Previous studies have reported varying levels of weed control by dazomet. As MITC is highly water soluble, mobile in soil, and volatile, inconsistencies in dazomet efficacy may be related to post-application practices of tilling, rolling, irrigation, and tarping. Therefore, the objective of this study was to analyze the effect of two practices commonly performed following dazomet application: tarp treatment (tilling, rolling, irrigation, and tarping), and water-seal treatment (post-irrigation at 0, 1, 2, and 3 days after application) on MITC concentration, distribution, and persistence in sandy soil. Field studies were conducted at Sandhills Research Station in Jackson Springs, NC, USA, in 2022 and 2023. MITC concentration and persistence varied between treatments and years. In 2022, MITC concentrations were notably higher in the tarp treatment compared with the water-seal treatment, whereas in 2023, the difference between treatments was less pronounced and more soil depth– and sample timing–dependent. Both treatments presented longer persistence, up to 168 hours after application (HAA), in 2023 compared with 120 HAA in 2022. In addition, MITC was highly concentrated in the top 15 cm of the soil and was detected as deep as 31 cm down from the soil surface in both treatments across both years.