The first sea shipments of USA Thompson Seedless grapes have now arrived in Australia. After a nervous wait most importers are cautiously optimistic about the future of their Thompson Seedless programs. Thompson Seedless is Australia’s most popular grape variety and three years ago USA Thompsons were a huge hit with Australian consumers. That was before the previously unknown vinegar fly Drosophila suzukii made its presence felt. For the 2010 and 2011 seasons Biosecurity Australia required USA grapes to be fumigated with methyl bromide to control this pest. Methyl bromide fumigation seriously shortens the shipping/marketing life of table grapes. Some varieties (including Thompson Seedless) are particularly sensitive to this fumigant. As long as methyl bromide was to be part of the program, sea freight Thompsons were not.
Biosecurity Australia then approved an alternative treatment for table grapes imported from the USA. This treatment involved a combination of SO2/CO2 fumigation followed by cold treatment for 6 days at a pulp temperature of minus 0.5°C. Cold treatment was able to be performed prior to shipment or in-transit.
At this stage the sea freight Thompsons appear to be in similar condition to that of the same lines that arrived by air 2-3 weeks ago. We won’t know for sure until we see them on the retail shelf but at this stage better lines have acceptable levels of damage.
Prior to the arrival of the sea freight Thompsons, the Australian market was well supplied with Flame Seedless. The combination of cold treatment and the 3-week voyage led to inconsistent arrivals of Flames. It is likely that weaker lines of Thompson will develop the same distinctive glassy berries that we saw in some Flame shipments.
Irrespective of variety the future of USA grapes in Australia depends on growing lines that are robust enough to withstand cold disinfestation and managing the disinfestation process to minimise exposure to temperatures below minus 0.5°C. The USA industry will continue to try to convince Biosecurity Australia to approve a higher temperature for cold disinfestation.