Antibiotic use in mandarin orchards in Thailand


Antibiotic use in plants has received relatively little attention, partly due to the small size of the sector relative to other sectors (WHO 2015). In Thailand, antibiotic injection into mandarins has been brought to attention by the disclosure of photos of syringes filling mandarin trunks in orchards through the media in November 2018 (Thai PBS 2018). The story illustrated practices of orange growers in the north of Thailand, the use of antibiotics in the plant sector meant for human use and led to concerns about antimicrobial resistance among health professionals and others working on this issue. As the news was widely spread at the time, it was creating a sense of fear amongst consumers of mandarins. Mandarins were labelled as toxic fruits in some media outlets (Thaiger 2018). Meanwhile the growers were reluctant to share about this practice due to fear of ban on usage. To attend this, we traced the development of mandarin orchards and citrus greening disease in Thailand, visiting many of them in different provinces to understand their practice.

Photo by @borderpharmacist

According to the growers, antibiotics were used to remedy Citrus Greening disease, a deadly disease that led to a major decline of the citrus industry around the world. Antibiotics have also been used in orange orchards in the USA, where growers in Florida state were allowed to spray antibiotic solution to protect their crops. However, their efficiency and mechanism are still debatable (McKenna 2019).

Despite the lack of investigation of the properties and toxicity of the antibiotics used, the mandarin growers in Thailand feel obliged to inject their trees due to the precarious circumstances. In Thailand the notion of citrus greening disease has been inextricably intertwined with international communities in many aspects, since the coming of researchers of the Food and Agriculture Organization (FAO) in 1970s, and growers’ experience with the disease for decades, as will be outlined below.

Farmer showing his equipment. Photo by Thitima Urapeepathanapong

Spread and impact of citrus greening disease 

Citrus greening disease is a disease of rutaceous (citrus) plants, which are widely planted all over Thailand. Sweet orange and mandarin are more severely damaged by the disease compared to other species. Although less susceptible, the Mexican lime (Citrus aurantifolia), and the ’Dok Kaew’ Murraya paniculata are also host to the disease, which poses a problem since they are both common in Thailand (Bové and Garnier, 1984; Coletta-Filho et al. 2004).

During the late 1960s-1970s when orange orchards were destroyed by the Citrus Greening disease, international organizations had already begun working jointly with the Department of Agriculture of Thailand (DOA) to address other pest problems. In 1969, the Pesticide Research Branch of the DOA was supported by a UNDP/FAO Programme for Strengthening Plant Protection Services. To cure the disease, the DOA suggested treatments that take into account psylla distribution, natural barriers and exclusionary domestic quarantines, and the use of a tolerant variety (Schwarz, Knorr, and Prommintra 1973). However, due to the limited spread of the disease, at the time, most growers were not very involved.

The disease spread rapidly in the late 1990s to early 2000 in Rangsit, Pathumthani province. Rangsit hosted a major orange production, since growers relocated from Bang Mod to Bangkok due to drought, flood and saline intrusion, and subsequently vastly expanded cultivated areas with intensive production. The disease also spread because the government encouraged farmers to expand their plantation, and in response to a tropical storm destroyed half of the citrus trees in Rangsit, rapidly distributed grafting stems from various sources to the growers. The spread of the disease further increased due to cross-contamination between orchards, industrial farming and the relocation of farmers to other provinces. As a result of infected scions (a detached living portion of the plant, such as a bud or shoot), which were brought in without detecting the pathogen, not more than five years later the same infection cycle occurred again. Consequently, a majority of growers repeatedly lost money. Due to massive investments in production, the unpredictable citrus greening crisis really frustrated growers who experienced major difficulty and financial loss in the first and second disease outbreak.

Antibiotics: Not an option, but a necessity

In general, growers are unable to detect the disease because Candidatus Liberibacter asiaticus (CLas) exists in its tissue (phloem). The symptoms are only visible when the pathogen is already distributed through roots and leaves. The growers, in general, are unable to conduct a diagnosis through laboratory (PCR) testing planting. Most growers know that to prevent citrus greening disease, they should cultivate pathogen-free scion and use alcohol to clean scissors before cutting trunks. But this is not a very practical solution.

Thai growers learned to use antibiotics from a university plant pathologist, who conducted her studies of antibiotic trunk injection in 2004-2005.  When she realized many growers replicated her experiments and began trying by themselves, she disseminated a manual. During the early years, after using 20-40 syringes per tree for a while, farmers increased the quantity of the antibiotics while also adapting to PVC pipes to save time and labour. Moreover, they not only injected directly into the trunks, as was the instruction, but also targeted branches.

Since the notion of antibiotics injection spread out to all orange growers, yields have steadily increased overall. The farmers explained how the orchards were ‘reborn’ via ampicillin: a thin and weak trunk became a strong stem, a pale and yellow leaf returned to a fresh green, a bruised and black fruit became a bright orange. 

Since growers whose orchards were hit by citrus greening disease more than once, and lost large investments, they ultimately have relied on antibiotics injection. Most growers depend on antibiotics as prevention. It was believed unless they used antibiotics, fruits would fall in harvesting time and crops would be spoiled. They have never fallen since the injection. In addition, most growers treated antibiotics as human medicine, which are safe to use.

However, the regulation of injections is still problematic. Agricultural law only prohibits the use of chemicals that are on the list of hazardous substances, while ampicillin and streptomycin are not on this list. In addition, the law on public health and medicines only prohibits illegal sale of antibiotics, not the use. So, this also does not address how or whether antibiotics can be used in plants.  While the issue is mentioned in the NAP in agricultural part, no elaborative plans exist as of yet to deal with this. Consequently, for mandarin growers, using antibiotics is their rational choice, for continuing their lives.


In conclusion, this case study has shown the complexity of antibiotic use in the agricultural sector, which requires multiple approaches to understand instead of ‘blame and shame’ as behavioral practice. With a social science approach, it helps us clarify the rationale of these growers’ practices, which intertwine with economic, legal, and environmental perspectives.

Points of discussion

Why do you think citizens were so shocked when they learned about the injections in mandarins? 

Do you think mandarin growers are to blame for their choice to use antibiotics? 

What policy strategies would be necessary to solve the use of antibiotics among these growers? 

Pedagogical notes

Do students even think about the plant sector when they think of AMR? You could start this case study by first asking students to list all sectors affected and see how many names agriculture, and within that how many even think of citrus plants. 

It’s important here to have students understand the ecological history which leads people to take on certain practices. In this case, the grower’s use of antibiotics is a response to several major disease outbreaks and large financial losses and a lack of efficient traditional methods to respond this. Antibiotics are an easy way out. This links to the idea of antibiotics as an infrastructural problem (Chandler).



  • Thitima Urapeepathanapong

Society and Health Institute, the Ministry of Public Health, Thailand, and The Antimicrobials in Society (AMIS) Project.


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