MAINTAINING BIOSECURITY AND MARKET ACCESS IN THE AUSTRALIAN STRAWBERRY INDUSTRY FOLLOWING METHYL BROMIDE PHASE-OUT

Abstract

The Australian strawberry nursery industry has trialled alternatives to methyl bromide (MB) for soil disinfestation since 1995. Generally, the alternative fumigants registered in Australia (chloropicrin (Pic); 1,3 dichloropropene (1,3-D)/ Pic; metham sodium; dazomet) have controlled soil-borne pathogens and weeds to similar levels as MB (e.g. 1,3-D/Pic reduced Rhizoctonia solani from 65 to 1 pg DNA/g soil). However, due to their low vapour pressures, the registered alternative fumigants have sometimes caused phytotoxicity in strawberry transplant crops (up to 40% yield loss). This is exacerbated under the cold conditions (<5°C soil temperature) and heavy soils present in the nursery industry. Alternative fumigants with higher vapour pressures, such as methyl iodide and ethanedinitrile, have given more consistent yield responses in trials and are currently undergoing registration in Australia. As long-term solutions, trials are investigating soil-less systems (e.g. coir substrates) and non-pesticide methods (e.g. mycofumigation) as alternatives to MB and other fumigants for transplant production. In addition to finding effective alternatives, regulatory issues are forcing industry to apply for exemptions to retain the use of MB. For example, some states only grant certification or accept entry of strawberry transplants if they are produced in soils treated with MB. A key issue is that the biosecurity risk of carrying pathogens in transplants produced under alternative systems is difficult to quantify. Our research has commenced developing and applying molecular and traditional tools to better define pathogen thresholds that meet certification of strawberry transplants. Preliminary data suggests that the incidence of crown rot caused by Phytophthora cactorum in transplants grown in MB-treated soil may be in the range of 0.01-1.0%, but the development of molecular-based screening and appropriate sampling strategies is important to better define certification standards for this and other pathogens.