Along a busy road east of Yogyakarta, postgraduate student Ika Afifah Nugrageni checks citrus trees on a small plot as two local Javanese farmers watch on.
Ms Ika, who is studying at Indonesia’s Universitas Muhammadiyah Gresik (UMG), is looking for a tiny pest that carries one of the most feared citrus diseases in the world.
Huanglongbing, also known as HSB or citrus greening disease, can devastate citrus trees, causing tree decline and death.
Ika Afifah Nugrageni helps farmers check citrus trees for the Asian citrus psyllid. (ABC Rural: Emma Field)
Researchers have labelled HSB the “cancer of citrus” because it’s fatal, with no known cure.
The bacterial infection is mainly spread by the Asian citrus psyllid insect, hitting every major citrus-growing region across the globe, except for Australia.
To keep it that way, the federal government has partnered with researchers in Indonesia and China to learn more about HSB detection and control.
‘We learn from each other’
Australian government agency, the Australian Centre for International Agricultural Research (ACIAR), allocated nearly $1.8 million to the research project over five years.
As part of the project, UMG’s faculty of agriculture monitors field trials around the village of Kembanglimus, in the Borobudur district of Magelang, in central Java.
One of the orchards is owned by third-generation Javanese farmer Nurofik.
Speaking via an interpreter, Mr Nurofik told the ABC he was happy to help the study.
“We learn from each other,” he said.
“If our friends from UGM need land to do research on, it’s beneficial for both of us.“
Wardi helps his younger neighbour farm citrus and other fruits. (ABC Rural: Emma Field)
The Borobudur region does not have a high level of HSB, but farmers are learning to detect and deal with incursions.
“Because farmers take the seedling from [a neighbouring region] which is an endemic location of huanglongbing, we must be prepared,” Ms Ika said as she inspected the young citrus trees.
Mr Nurofik, and his older neighbour and mentor Mr Wardi, said they did not know a lot about managing the psyllid, or the disease.
“I’ve heard of and seen it, but it doesn’t happen here,” Mr Wardi said.
“But I don’t have much information about how to handle the disease.”
The Asian citrus psyllid transmits the citrus disease huanglongbing. (ABC Rural: Emma Field)
No cure for ‘citrus cancer’
Once trees are infected, the leaves turn yellow, fruit becomes bitter and the trees die within five years.
The only way to effectively control HBS is to rip out the infected trees.
Tangerine trees are commonly grown in Indonesia, offering high-yields and nutritious fruit. (ABC Rural: Emma Field)
In the US, HSB has devastated citrus production in Florida, California and Texas, while Australia’s neighbours, Indonesia, East Timor and Papua New Guinea all have recorded instances of the disease.
More than 100 million trees have been destroyed in South and Southeast Asia due to HSB.
An incursion in the US and Brazil in 2024 resulted in an orange juice shortage, and soaring global prices.
Threat to Australia’s $1b industry
Citrus is Australia’s third most valuable horticulture crop, behind berries and almonds, with an estimated worth of $1 billion.
Australian citrus exports make up a little over half that value, with about 30 per cent of the country’s oranges, mandarins, grapefruit, lemons and limes sent overseas.
The Australian citrus industry is worth $1 billion. (ABC Mildura: Tamara Clark)
The disease is considered the biggest biosecurity threat to local citrus production and strict biosecurity controls and surveillance measures are in place.
A potential incursion was prevented in 2016, when Australian border authorities found live psyllids on a lime plant in the luggage of a traveller from Bangladesh.
Disease destroys livelihoods and food security
Back in Indonesia, Professor Siti Subandiyah from the UMG department of plant protection leads the ACIAR project for the university.
She said HSB was hard to detect and control because it was not only spread by the psyllid but also by the movement of infected plant material.
Given most Indonesian farms are small and have limited shelter, money and food, Professor Siti said the disease affected their livelihoods and the health of their families.
“The farm will not be profitable [and] it affects the livelihood of the family, because the income will be declining,” she said.
Siti Subandiyah says addressing HLB in Indonesia is critical for food security. (ABC Rural: Emma Field)
Professor Siti said eradication of HSB was “very difficult”, as there was poor awareness among growers and no local compensation scheme.
“We can’t just have one farmer follow the recommendation; it has to be in a wide area management,” she said.
“With many smallholder farmers, it is very difficult to organise, to coordinate the work.”
An Indonesian agriculture student is learning about citrus production and disease control. (ABC Rural: Emma Field)
The university said it was educating citrus farmers and testing the effectiveness of insect repellents and traps to kill the psyllid.
Professor Siti said the Australian-funded project was incredibly important to small-holder farmers.
“Although we still have to import [some citrus], for domestic production it will help the smallholder farmer to get income from this commodity,” she said.
“And also feeding us with a good fruit, because citrus is very good fruit for health.”
Australian citrus rootstock is being tested for resistance and response to HSB. (ABC Rural: Emma Field)
Aussie citrus testing in Indonesian greenhouses
The project also includes testing Australian and US citrus rootstock for HBS tolerance at UGM’s research farm.
Professor Siti said it would be a massive breakthrough if they found plants that were resistant.
But she said it was not an easy task.
“Worldwide, we haven’t found a resistant one yet,” she said.
For Alan Soffan, the head of UMG’s Agro-technology Innovation Centre, the project is important on many levels.
“We have citrus, Australia has citrus, so we can share the knowledge and share the problem, to improve our production, our quality of citrus, to feed the world,” he said.
Dr Soffan said it also aligned with Indonesian President Prabowo Subianto’s aim to achieve food self-sufficiency within five years.
“Our president says agriculture is the foundation of national stability,” he said.
ABC reporter Emma Field travelled to Indonesia as part of The Crawford Fund journalism scholarship, with support from Department of Foreign Affairs and Trade, and The Association of Southeast Asian Nations Australia Centre.