A cold treatment for postharvest control of western flower thrips on strawberry runners

In 1998–99, outbreaks of Frankliniella occidentalis (Pergrande), western flower thrips (WFT), caused extensive damage to strawberry crops in the Yarra Valley, Victoria. These crops were within 30 km of Toolangi where over 80% of certified strawberry runners for Australia are produced. Commercial growers store runners for various periods of time at temperatures as low as –2°C. Cold temperature disinfestation was evaluated as a potential strategy in a contingency plan to prevent the spread of WFT on strawberry runners. Western flower thrips at various life stages on gerbera flowers (on which they were reared), were placed in small bags, made from the plastic liners used in commercial strawberry runner cartons, together with strawberry runners and exposed to –2°C for periods of 1, 2, 4, or 8 weeks. All WFT died within 4 weeks. Additional experiments were conducted in which WFT, in bags with runners or on gerbera leaf disks in petri dishes, were exposed to –2°C for 3 weeks. Only a few WFT survived these treatments; however, they were moribund. When they were assessed 2 days after completion of the exposure period, all WFT were dead. It was concluded that strawberry runners carrying WFT can be disinfested by exposing WFT to –2°C for 4 weeks and that this should be achievable under commercial conditions.