CRITICAL CHALLENGES FOR THE PHASE-OUT OF METHYL BROMIDE IN THE AUSTRALIAN STRAWBERRY INDUSTRY

The Australian strawberry industry has trialled substitutes to methyl bromide (MB)/chloropicrin (Pic) mixtures for soil disinfestation since 1995. The research supported the registration of Pic and 1,3-dichloropropene (1,3-D)/Pic products in Australia, and these were rapidly adopted by the strawberry fruit industry in 2006. This transition reduced emissions of MB to the atmosphere by 120 t pa. Generally, the substitute fumigants have delivered similar fruit yields to MB/Pic, but the incidence of diseases caused by previously obscure pathogens, such as Fusarium spp. and Macrophomina phaseolina, has increased. In contrast, research in the strawberry runner industry shows that the registered substitute fumigants (viz. 1,3-D/Pic, Pic, dazomet and metham sodium) can cause severe incidences of phytotoxicity, and crop losses of up to 40%. This is related to the high organic matter (5-10%) and clay content (>50%) of soils in Toolangi, Victoria, where strawberry runners are grown. These factors combined with cold temperatures at fumigation (5-12°C) have contributed to long retention times of substitute fumigants in soil. Alternative fumigants with high vapour pressures, such as methyl iodide, have successfully disinfested soils in these environments, but were recently withdrawn in Australia. Certification authorities do not approve the use of substitute fumigants for runner production, and the industry currently applies for 29.79 t of MB pa under a critical-use exemption. The industry does, however, produce its early generations of runners using coir-based substrates, which reduces the need for disinfestation with MB/Pic. These systems are not economically feasible for later generations because runner prices would need to increase by more than 500% to make them viable. Current research is investigating the combined use of low-rate fumigants and herbicides for soil disinfestation in the runner industry, with the aim of reducing the risk of crop phytotoxicity from individual products.