Alternatives to methyl bromide for weed control in perennial ornamental crops and conifer seedlings

The soil fumigant methyl bromide is being phased out in accordance with the Montreal Protocol and will not be available in the future. Experiments were conducted to identify fumigants and herbicides to replace methyl bromide for weed control in conifers and ornamental crops grown in the field and in containers under Michigan conditions. The fumigants methyl iodide, metham sodium, 1,3-dichloropropene, dazomet, and chloropicrin were evaluated in a field experiment. All of these fumigants provided good weed control, except methyl iodide 50% plus chloropicrin 50% (224 kg/ha) tarped and metham sodium (701 L/ha, 1:4 water) not tarped. Euphorbia polychroma, Echinops bannaticus 'Blue Globe', Lavandula angustifolia 'Hidcote Blue', Hosta fortunei 'Twilight PP14040', Artemisia schmidtiana 'Silver Mound', Chrysanthemum x superbum 'Snow Lady' and Coreopsis verticillata 'Moon Beam' growth was not affected by any of the fumigants. Herbicides were applied to several ornamental and conifer species to evaluate crop tolerance and weed control in the field and containers. There was considerable variability in crop tolerance among the species evaluated. The woody ornamental species Picea glauca var. 'Dwarf Alberta', Taxus x media var. 'Brownii', and Thuja occidentalis var. 'Holmstrup' were tolerant of most herbicide treatments, while other species were sensitive to one or more herbicides. Terbacil gave excellent weed control, but caused injury on most species. Flumioxazin and isoxaben plus trifluralin were the safest treatments on the species evaluated and gave good weed control.