Dose response of weed seeds and soilborne pathogens to 1,3-D and chloropicrin

InLine (Dow AgroSciences LLC, Indianapolis, IN, USA), a commercial formulation of 1,3-dichloropropene (1,3-D; 61%) plus chloropicrin (33%), is one of the potential replacements to methyl bromide for soil fumigation. The efficacy of 12 InLine concentrations (80-19,520 μmol kg−1) to control five species of weed seeds and four soilborne pathogens was evaluated in a laboratory dose-response study after 24 h of exposure to fumigants in a sandy loam soil at 20 °C in microcosms. Logistic dose-response models were used to estimate the effective concentration to reduce weed seed and pathogen viability by 50% (LC50) or 90% (LC90). Among the weeds, the seed of Portulaca oleracea was the most sensitive to soil fumigation with InLine (LC50=352 μmol kg−1, LC90=583 μmol kg−1), followed by Stellaria media and Polygonum arenastrum with LC90 values of 780 and 1636 μmol kg−1 soil, respectively. The seeds of Malva parviflora and Erodium cicutarium were not sensitive to fumigation up to the highest InLine dose of 19,520 μmol kg−1 soil. Among the pathogens, Pythium ultimum (LC50=30 μmol kg−1 soil, LC90=46 μmol kg−1 soil) was the most sensitive and Verticillium dahliae (LC50=625 μmol kg−1 soil, LC90=2735 μmol kg−1 soil) was the least sensitive to InLine fumigation. Phytophthora cactorum and Fusarium oxysporum exhibited intermediate susceptibility to this soil treatment (LC50⩽397 μmol kg−1 soil, LC90⩽1113 μmol kg−1 soil). In this sandy loam soil, InLine at a concentration of 1636 μmol kg−1 reduced the viability of Portulaca oleracea, S. media, Polygonum arenastrum seeds and all fungi pathogens tested (except for V. dahliae) by 90% at 20 °C after 24 h exposure.