Weed Community Composition in Tree Fruit Nurseries Treated with Methyl Bromide and Alternative Fumigants

Abstract

Many agricultural cropping systems have relied on methyl bromide (MeBr) for pest control, including weeds, for decades. Alternative fumigants are being sought worldwide because MeBr has been identified as an ozone-layer depleting substance. Weed communities respond dynamically to alterations in management systems. Thus, transition from MeBr to alternative fumigants may cause shifts in weed communities. This hypothesis was tested in four commercial fruit nurseries in California, USA. Treatments included nonfumigated control, MeBr (98%), iodomethane (50%) + chloropicrin (50%), 1,3-dichloropropene (1,3-D), 1,3-D (61%) + chloropicrin (35%), and 1,3-D (62%) + chloropicrin (35%) applied subsurface. All the fumigants reduced the population of common major weed species and had similar species composition as MeBr. None of the fumigants, including MeBr, controlled species such as Medicago polymorpha, Lotus purshianus, Malva parviflora, Conyza sp., Senecio vulgaris, and Sonchus oleraceus. This study suggested that, fruit nurseries transitioning from MeBr to alternatives may not see an immediate shift in weed communities. However, Additional weed control measures will be required to manage weed species of the Asteraceae, Fabaceae, and Malvaceae family that are not controlled by either MeBr or the alternate fumigants.