It is not just the physical borders that need to be protected to prevent crop diseases making their way to northern Australia — we must also be wary of the wind.

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Research from the University of Western Australia’s Institute of Agriculture has found foreign insects blown hundreds of kilometres across the ocean may have brought plant disease strains all the way from East Timor and Papua New Guinea to the northern part of the country.

During the three-and-a-half-year project funded by the Cooperative Research centre for Plant Biosecurity, PhD student Solomon Maina identified a disease strain in the Kimberley’s Ord Valley, not found anywhere else in Australia.

His supervisor Adjunct Professor Roger Jones said the unique match between Zucchini Yellow Mosaic Virus (ZYMV) in Kununurra and East Timor, backed up their theory that plant diseases could be pushed into Australia via monsoonal winds.

“What we were looking for was what we call genetic connectivity, where a sequence from one of our northern neighbours such as East Timor matches the sequence found in Australia,” he said.

“We can now say the tropically adapted strain got established in Kununurra and is the one that’s causing the bigger epidemics in the cucurbit crops [such as squash and pumpkin].

“They have a unique problem in that the disease is being caused by a different strain than everywhere else in the country.”

Professor Jones said it was an easier journey for pathogens to cross from South East Asia than you might think.

“It has been recorded before these kinds of aphids; in the US they have been recorded blowing from the south to the north in jet stream winds and settling down and being deposited in crops which are huge distances away from where they originated.”

Increased surveillance needed

Professor Jones said it was a significant research for the northern horticultural industry where severe ZYMV epidemics in melon and pumpkin crops threatened its long-term viability.

The aphid-borne virus, causes major losses in yield and quality of cucurbit crops including cucumber, pumpkin, rockmelon, squash, watermelon and zucchini.

The project also uncovered genetic matches between Papaya Ringspot Virus in cucurbits across northern Australia and Papua New Guinea, and Sweet Potato Feathery Mottle Virus from sweet potato from East Timor and Kununurra.

Professor Jones said the research emphasised the need for increased surveillance of vira-pathogens to reduce the biosecurity threat to crops in the north.

“We can’t really prevent aphids building up on crops in another country, and you can’t influence wind direction and the climate,” he said.

“But what you can do is have surveillance targeting crops to see if any other new things have arrived.

“I think it’s important to keep going with this kind of research, with other crops in mind than just cucurbits and sweet potatoes; it would be good if there was funding available to do that in the future.”

Trapping aphids on the ground

Professor Jones said he had also been working with growers in the Ord Valley on another project funded by Royalties for Regions, which had uncovered more about the aphid species and diseases affecting cucurbit crops.

He said he hoped the three-year project between the Department of Primary Industries and Regional Development, the Kununurra Research Station, UWA and local growers would find a way to manage mosaic viruses in the Ord Valley and limit its impact on crop production.

“It gave a lot of understanding of what was going on and where the aphids and virus was coming from and what kinds of aphids were present, because there was very little information known for the Ord,” he said.

“We got information from five sites where aphids were trapped every week over a three year period, so we knew what the numbers were and when they were building up at different times of year.

“There were six aphid species found up in the Ord, [so] there may be other species blown over from East Timor or Indonesia.”

Local grower Christian Bloecker said one of the biggest challenges for melon farmers in the Ord was controlling aphids and the damage caused by ZYMV on their crops.

He said this new research would go a long way to giving growers the best line of defence against pests and disease.

“What it does mean is that we’ve always got to be on the lookout, which means on the farm in terms of hygiene we need to be mindful of the rotation of crops, making sure there’s no cucurbit weeds near our plantings,” he said.

“It would be great to keep that going because it gives is a little bit of warning on when we need to be on the lookout for aphids and also for the virus.

“There’s also potential to look at varieties that have some kind of resistance to the aphids and ZYMV and the use of barrier crops or alternative cropping systems to delay the arrival of the aphids and virus; that’s where the future research lies.”