Latest Treatment Methods and Integrated Control Measures for Citrus Huanglongbing
I happen to have just written an analysis article on Huanglongbing in southern Jiangxi, titled "Citrus AIDS" Huanglongbing Spreads Across Gannan, the World's Largest Navel Orange Producing Region: A Natural Disaster, but Even More So a Man-Made One, which can serve as an answer. There is currently no way to cure Huanglongbing, but if local authorities can decisively adopt certain measures and carry out unified prevention and control, Gannan can still be saved.
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If you have seen the sci-fi film Interstellar, you must have been deeply impressed by the crop blight spreading across the Earth. On some future day, crops contract an incurable disease, and entire fields of corn and okra die, leaving humanity able only to wait for death.
Science fiction mirrors reality. In 2015, in the Jiangxi Gannan region, the world's largest navel orange producing area, large areas of citrus were infected with Huanglongbing, known as "citrus AIDS," and many farmers could only cut down entire plots of navel orange trees they had planted for years, and did not dare to plant again.
In response, the Harvest Research Office, through investigation and statistics, found that the large-scale outbreak of Huanglongbing in Gannan was closely related to years of large-scale unscientific cultivation in the region. What appeared to be a natural disaster was in fact a man-made one.
Figure 0: Comparison of navel oranges with Huanglongbing and normal navel oranges
"Citrus AIDS" Huanglongbing is an incurable disease of citrus; it cannot be treated, only cut down
Huanglongbing is a devastating citrus disease transmitted by the Asian citrus psyllid, and it is also a malignant disease of particular concern in domestic citrus-producing areas. Like "cancer cells," it spreads and rampages very quickly, and is called "citrus cancer" and "citrus AIDS." Huanglongbing has two characteristics:
1. There is no cure; once a citrus tree is infected, it can only be cut down and removed.
2. It spreads extremely easily. The Asian citrus psyllid acquires the pathogen by feeding on diseased trees and then transmits it, and the speed of spread is very fast. As the main domestic navel orange producing area, Ganzhou City is suffering from Huanglongbing, and the trend is worsening.
1. Huanglongbing is a worldwide problem and cannot be cured
Huanglongbing is believed to be caused by a bacterium specifically dwelling in the phloem tissue of citrus. Its transmission routes include grafting and transmission by the Asian citrus psyllid. At present, all known citrus varieties and closely related citrus species can be infected with Huanglongbing. Infected plants not only fail to produce economic value, but highly susceptible varieties such as navel orange and grapefruit will gradually decline and die within a few years. Once a fruit tree is infected, there is no cure, and it can only be cut down and removed.
2. The Asian citrus psyllid spreads the disease, and poor management can lead to large-scale transmission
The Asian citrus psyllid is a major pest during the new shoot stage of citrus, and it is also the transmission vector of citrus Huanglongbing. Adults mostly lay eggs on the tender shoots of diseased trees, and after hatching, the nymphs suck the sap from the tender shoots, which can produce large numbers of pathogen-carrying adults. The adults then fly to new plants and transmit Huanglongbing. The main management strategy for Huanglongbing is to use insecticides to control the psyllid, dig out and remove infected plants, and cultivate pathogen-free seedlings. Poor field management mainly manifests as:
(1) Failure to control the psyllid in a timely manner, producing large numbers of pathogen-carrying adults.
(2) Failure to promptly cut down and dispose of plants found with Huanglongbing, allowing them to become sources of infection.
(3) Excessive use of pesticides and fertilizers causing soil compaction, resulting in root rot.
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One outbreak of Huanglongbing destroys 10 years of hard work for Ganzhou fruit farmers
1. In 2014, Ganzhou's navel orange output accounted for 48% of China's, a very high concentration
According to statistics, in 2014, the navel orange output in the Gannan region reached 1.23 million tons, accounting for about 48% of domestic output. It is truly China's largest navel orange producing region. In 2014, Gannan's navel orange planting area was 1.68 million mu, ranking first in the world for single-region navel orange planting area and third in the world for output. High concentration promoted the development of the citrus industry, but it also brought the risk of disease transmission.
2. Cutting down fruit trees destroys a decade of farmers' hard work in an instant
In 2012, Huanglongbing began to break out on a large scale. Although according to statistics from the Ganzhou fruit industry department, over three years the navel orange planting area fell from 1.78 million mu to 1.68 million mu.
But according to non-governmental surveys, the situation appears even more serious. Over the past 3 years, in Xunwu, Anyuan, and Xinfeng, the three counties with the highest concentration of Gannan navel orange planting, the area of diseased trees cut down reached almost one third. In Xunwu County, which has the largest navel orange planting area, the planting area decreased from 600,000 mu to more than 400,000 mu. In Xinfeng County, in the autumn and winter of 2013, 1.5247 million infected plants were confirmed, with an incidence rate of 11.8%. Moreover, Huanglongbing has an incubation period, and in the following years diseased trees will continue to appear.
Some farmers said that navel oranges take about seven or eight years from planting to full production, and many diseased orchards are now exactly in their full-production period. This outbreak of Huanglongbing destroyed nearly ten years of their hard work.
Farmers suffer heavy losses; replanting becomes risky investment, forcing them to go out to work again
1. Income losses that year were severe
Chen Hong, a farmer from Guanzhou Village, Nanqiao Town, Xunwu County, Jiangxi, began planting navel oranges and mandarin oranges six years ago, and at most his family had nearly 1,000 fruit trees. As Huanglongbing broke out on a large scale, he cut down nearly 300 fruit trees in 2013 and another six or seven hundred in 2015, almost all of them. Mid- and small-scale growers like him are very common locally. According to a survey by the Harvest Research Office, in Wangwu Village, Chengjiang Town, Xunwu County, entire plots of navel orange trees were cut down. Most of the fruit groves in Guizhumao Town, Xunwu County, were also cut down, and after cutting the trees most local people went back out to work.
2. Newly planted fruit trees take 3 years to bear fruit
Cutting down navel orange trees cultivated painstakingly for many years is truly a last resort. One mu of navel oranges has 60 fruit trees, with income of 10,000 to 15,000 yuan. But navel oranges take about 3 years from new seedling planting to fruiting, and about 5 years to enter full production. The earlier water, fertilizer, and management inputs per mu require tens of thousands of yuan in costs, so the investment is very high.
3. Huanglongbing may recur at any time, making the risk even higher
After cutting down the navel orange trees, many farmers do not dare to plant navel oranges again, because navel oranges take three years to bear fruit, and Huanglongbing is transmitted by the psyllid, so replanting carries great risk and they may be infected again at any time. If they switch to other crops, some plant oil tea and some plant vegetables, but the income is not as high as navel oranges. For example, one mu of oil tea, after reaching full production, brings an annual income of 3,000-4,000 yuan, far less than planting navel oranges. Therefore, some farmers simply let the land lie fallow and go out to work, or change careers and do other business.
Everyone following the trend of planting led to an overly uniform local ecological environment, laying hidden dangers for the disease outbreak
1. The Gannan region was long impoverished, and planting navel oranges was an important way to become prosperous locally
The Gannan region is one of the country's larger contiguous poverty-stricken areas, and planting navel oranges is an important local way to become prosperous, because the area is especially suitable for growing navel oranges. After reaching full production, one mu of navel oranges can yield an output value of more than 10,000 yuan, so there is a saying that "one navel orange tree is equivalent to three pigs." Through large-scale navel orange planting, the per capita net income of farmers in the Gannan region rose from 4,182 yuan in 2010 to about 6,970 yuan in 2014.
2. The prosperity effect made local people follow the trend of planting navel oranges
Calculating on the basis of 60 trees per mu and each tree producing 100-200-plus jin of navel oranges, with a market price of about 1.5-2.9 yuan, the output value per mu of navel oranges is close to 20,000 yuan. Such a prosperity effect attracted farmers to plant in large quantities. Many people dug up previously planted crops such as oil tea and switched to navel oranges, and many former mountain forests were also converted into fruit groves. Not only farmers planted trees; local shop owners, teachers, and civil servants also planted navel oranges in almost every household, and at the same time many outsiders came to Ganzhou to rent mountains and open groves to plant navel oranges.
According to statistics, the navel orange planting area in the Gannan region grew rapidly from more than 300,000 mu in 2000, reached 1 million mu in 2005, and reached 1.78 million mu in 2012. Output also increased rapidly from less than 100,000 tons to about 1.23 million tons.
Figure 7: Gannan navel orange area and growth rate. Source: Ganzhou Municipal Fruit Industry Bureau
3. The government actively mobilized people's enthusiasm for planting navel oranges, but did not scientifically manage the red line well
It is understood that in a certain county in Gannan, in the early years, in order to mobilize the people's enthusiasm for planting navel oranges and accelerate escaping local poverty, the county government put forward the slogan "work in the office in the morning, go up the mountain in the afternoon," mobilizing party members and cadres to help farmers build orchards and plant navel oranges. This gave the people very strong confidence and fully mobilized society's enthusiasm for planting navel oranges, but the scientific red line was not drawn well.
Within a few years, the people of Ganzhou filled the mountains and fields with navel oranges, and even excavated and planted trees in the natural biological isolation belts between orchards. This destroyed the protective barrier of the ecological environment and created conditions for the psyllid to spread Huanglongbing. Although the government's approach mobilized farmers' enthusiasm and expanded the planting area, the lag in guidance and control measures for scientific planning and scientific planting was equivalent to multiplying the risk of a Huanglongbing outbreak several times over.
4. Ultimately this led to overly uniform varieties in the region and a fragile ecology, making Huanglongbing extremely likely to spread devastatingly
In agricultural planting, single-crop cultivation has always been a potential threat. From the perspective of natural laws, the problem of uniform species planting carries enormous safety hazards. If the planting structure is uniform and a region grows only one crop for a long time, soil fertility will decline, biodiversity will disappear, and pests and diseases will worsen.
Ecological principles tell us that the stability of an ecosystem depends on biodiversity. A complex ecosystem always has a greater capacity to respond to changes in the external environment than a simple ecosystem, and the stability of agricultural systems likewise depends on the diversity of agricultural biological varieties. Single-crop continuous cropping weakens biodiversity in the agricultural ecosystem, increasing instability and fragility and reducing resistance to natural disasters and pests and diseases.
In the Gannan region, according to statistics, 88% of navel orange varieties are the excellent-performing Newhall, while other varieties such as Bonanza and Navelina account for only 8% and 3%. Single-crop planting and uniform varieties create enormous hidden dangers for navel orange cultivation in the Gannan region.
Although uniform planting varieties help control quality and yield, they are not conducive to disease control. The outbreak of Huanglongbing in the Gannan region this time is deeply connected to overly uniform planting varieties.
5. Devastating ecological disasters caused by overly uniform planting varieties are common around the world
Large-scale single-crop cultivation of economic crops such as bananas and rubber has also encountered situations in which overly uniform global planting ultimately caused rubber blight and rubber tapping panel dryness to sweep the world beyond control, causing enormous losses. Taking banana Panama disease as an example, the banana variety "Gros Michel," once planted on a large scale uniformly around the world, became infected across more than 90% of its global area because of the outbreak of Panama disease, causing irreparable massive losses.
In the nineteenth century, the Irish used a potato variety called "Lumper" as a staple food, the largest single-crop cultivation attempt in human history up to that time. As a result, potato blight spread and caused the historically famous "Irish Famine." In September 1846, an estimated three quarters of the potato harvest was destroyed, causing the most severe famine in European history since the Black Death, and Ireland's population fell by half.
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With such a uniform ecology and without sufficient and effective management for prevention, control, and protection
1. The government did not pay attention to building effective ecological isolation belts, making it easy for the psyllid to spread Huanglongbing
Citrus Huanglongbing existed in the past as well, but the emergence of such a large-scale outbreak is closely related to the rapid, blind, and disorderly development of the industry. Existing studies have shown that in different citrus planting areas, using natural or artificial forests for ecological isolation can control the spread of the psyllid to a certain extent and also provide a living environment for the psyllid's natural enemies.
The purpose of ecological isolation belts is to prevent the spread of the psyllid. In ecologically standard citrus orchards, shelter forest belts (Chinese fir or other tree species) are planted according to plan, and natural forests and shrub belts can also be used to isolate orchards into blocks like tofu cubes, using physical isolation methods to control the harm of the psyllid. The specific arrangement can be reasonably made according to each village's land use conditions.
2. Villagers did not control area, and unmanaged orchards became outbreak points for "epidemics"
Driven by profit, Ganzhou fruit farmers planted navel oranges on all usable land in the mountains and fields, and even excavated and planted trees in the forest and shrub belts between orchards, creating large contiguous plantings. But once prices fell, they abandoned them, and unmanaged orchards became outbreak points for "epidemics."
Huanglongbing is mainly spread by the Asian citrus psyllid, and psyllid control is especially key in Huanglongbing prevention and control. Farmers in the Gannan region filled the mountains and fields with navel oranges, with no barriers between plots, making it easy for the psyllid to spread and contributing to the outbreak of Huanglongbing.
3. Soil deterioration and citrus root rot caused by excessive fertilizer and pesticide use breed disease and blight
Navel orange root rot is a common navel orange disease, mainly caused by orchard soil compaction and imbalanced soil nutrient structure, which cause the cortical layers of fibrous roots to turn brown and rot to varying degrees. After infection, tree vigor weakens and resistance to pathogens declines, making the trees susceptible to Huanglongbing.
In 2013, an expert team from the Fruit Tree Huanglongbing Research Office of the Zhongnan Agricultural Science and Technology Development Research Institute conducted field surveys in major navel orange counties such as Xunwu, Anyuan, and Xinfeng, and brought back multiple navel orange orchard soil samples for analysis and research. They found that the soil nutrient structure of the sample orchards was severely imbalanced and that high residues of chemical fertilizers and pesticides in the soil led to deterioration of the fruit tree growing environment, causing large-scale root rot in the orchards. This was also an important factor in the outbreak of navel orange Huanglongbing in the Ganzhou region.
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When Huanglongbing appears on a small scale, farmers are reluctant to cut down trees, worsening the disease -
1. Farmers are reluctant to cut down trees, causing the disease to spread
Huanglongbing often has an incubation period, and farmers often cannot quickly and accurately identify diseased trees, which is also one reason for its spread. But in the Gannan region, more farmers discovered the disease yet were reluctant to cut down the trees, or handled them improperly after cutting, which intensified the spread of the disease. Because cutting down the trees also cut off their only source of income. When a small-scale outbreak occurs, once the psyllid stays on a diseased tree, it will quickly spread the disease to other orchards.
2. Unified prevention and control is difficult to implement, and farmers refuse to dispose of diseased trees
The most difficult part of Huanglongbing prevention and control is unified prevention and control: as long as one household does not manage it, everyone suffers. Later, orchards with infection rates exceeding a certain proportion had to be completely cut down. From persuading farmers to plant trees back then to now persuading fruit farmers to cut down trees, grassroots cadres have encountered their most headache-inducing task.
The local government has already realized the seriousness of the problem and issued policies to subsidize farmers, such as sending technicians door to door to help farmers with control, and subsidizing 10 yuan for each diseased tree cut down. But because the subsidy is too small, many farmers still refuse to dispose of diseased trees.
Failure to pay attention to nursery stock quarantine and failure to mandate planting virus-free seedlings also laid hidden dangers for the Huanglongbing outbreak
1. Nursery stock trade spun out of control, leading to quarantine out of control
At the source of the navel orange industry, inadequate control of nursery stock is also an important reason for the Huanglongbing outbreak. Worldwide, planting virus-free seedlings is the standard for Huanglongbing prevention and control. But in the Gannan region, lack of oversight, failure to pay attention to nursery stock quarantine, and failure to mandate planting virus-free seedlings became one of the reasons for the spread of the disease.
Although there are laws and regulations such as the Regulations on Quarantine of Citrus Nursery Stock at Production Sites and the Implementation Plan for the Breeding and Supply of Virus-Free Citrus Nursery Stock in Ganzhou City, the navel orange seedlings purchased by farmers basically did not undergo strict quarantine, and large numbers of diseased seedlings flowed to the market. If people wanted to plant trees, they bought navel orange seedlings on the market, causing long-distance, large-scale human-mediated spread of Huanglongbing.
2. Farmers have weak awareness of disease prevention and introduce nursery stock from epidemic areas
The transport of scion seedlings, which should have been strictly controlled by the government, was not strictly implemented. This allowed a small number of nursery growers or citrus farmers with weak disease prevention awareness, driven by profit, to illegally introduce pathogen-carrying scion seedlings from epidemic areas such as Guangdong, Fujian, and Wenzhou, laying hidden dangers for the Huanglongbing outbreak.
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Through government intervention and active management, the United States has kept Huanglongbing within controllable limits
1. Foreign experience proves that Huanglongbing cannot be cured, but it can be effectively controlled
Huanglongbing is temporarily incurable, but losses can be minimized through prevention and control. California and Florida in the United States are also important navel orange growing regions in the world, and the U.S. citrus industry likewise faces the threat of Huanglongbing.
Figure 16: The U.S. citrus industry is also threatened by Huanglongbing
But relying on effective management and control, the United States reduced losses to a controllable level by following the approach of strengthening quarantine, mandating the use of virus-free seedlings, promptly digging out and removing diseased plants, and strictly controlling the Asian citrus psyllid. According to a report released in September 2011 by the National Agricultural Statistics Service (NASS) of the U.S. Department of Agriculture, compared with 2010, Florida's overall citrus planting area decreased by 2.3%, but citrus output increased by 4%.
2. The U.S. government invests huge sums every year to research and manage Huanglongbing in a unified way
In 2012, the U.S. Senate passed legislation to provide substantial funding each year for research on citrus Huanglongbing, in order to combat citrus Huanglongbing occurring in Florida and other major citrus-producing states. Large companies such as Coca-Cola also invested hundreds of millions of dollars to remediate citrus groves cut down because of Huanglongbing.
To effectively prevent Huanglongbing from expanding and spreading further, the U.S. Department of Agriculture (USDA) spent 30 million U.S. dollars to build a "Huanglongbing prevention and control" project. It is understood that the USDA divided this project into two parts: one part is a temporary solution: establishing a multi-department joint task force including the Animal and Plant Health Inspection Service (APHIS), the Agricultural Research Service (ARS), the National Institute of Food and Agriculture (NIFA), as well as national agricultural departments and agricultural industry groups. Citrus-producing areas are closely monitored, with the aim of minimizing losses caused by Huanglongbing.
The other part is establishing a long-term Citrus Disease Research and Education program (CDRE), with the aim of finding a prevention and control solution that thoroughly solves the plant diseases threatening the citrus industry.
In 2013, the United States also established a Huanglongbing management center together with American countries. It established standard operating procedures for responding to Huanglongbing and established mechanisms for risk communication, supervision, diagnosis, and management. It established regional information, communication systems, and network mechanisms. It set up plant management agencies to carry out regional prevention and control. It established a citrus grove recovery plan and dispatched expert teams for Huanglongbing prevention and control.
3. The United States' well-developed Huanglongbing prevention and control techniques
(1) Early diagnosis and early treatment: The University of Florida developed a device that can accurately detect Huanglongbing and can rapidly diagnose it before the human eye can judge, with an accuracy rate of 98%. After confirmation, the infected area is promptly sealed off, and the entry and exit of citrus nursery stock is strictly controlled to prevent it from spreading outward.
(2) Soil control: Different management methods are used according to different degrees of infection to maintain normal production. In addition, the environmental pH is controlled, and the pH of irrigation water and soil is lowered to protect the citrus root system and improve disease resistance.
(3) Heat treatment: Research has found that heat treatment technology can temporarily prolong the life of diseased trees, maintain a certain yield, and reduce losses. The next step will be to test and study the effects of heat treatment on large orchards.
(4) Biological control: The citrus psyllid parasitoid wasps Diaphorencyrtus aligarhensis and Tamarixia radiata have been proven to be the two most important parasitoid wasps of the Asian citrus psyllid and can effectively control the field population density of the psyllid. Their production and field release should continue to be expanded. In addition, fungi can also be used to prevent and control adult psyllids.
(5) Physical control: Setting traps to lure and kill psyllids, such as yellow sticky boards and insect traps. It is understood that the joint task force in Florida, USA, periodically inspects citrus orchards in its area, reports the test results, and analyzes the data by building statistical models. So far, a statewide Huanglongbing monitoring system has been established. In addition, the joint task force also uses the above measures to help growers control the Asian citrus psyllid, truly achieving the effect of unified prevention and control.
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The Gannan region needs unified prevention and control and an active response to the Huanglongbing epidemic
In Gannan, China, farmers planted on a large scale and in a uniform way, did not pay attention to building a stable ecological environment, did not reasonably control area, and applied large amounts of chemical fertilizers, causing imbalanced soil nutrient structure and environmental deterioration. After the epidemic broke out, they were unwilling to cut down trees, which intensified the spread of the disease.
The government, meanwhile, lacked responsibility in planting planning, mandatory nursery stock quarantine, and diversified planting varieties. After the epidemic broke out, it did not act quickly enough and did not have a good response plan, which likewise promoted the spread of Huanglongbing.
The outbreak of Huanglongbing in Gannan is not only a natural disaster, but even more a man-made one. In facing Huanglongbing, experience should be learned and actively responded to.
The Harvest Research Office has provided some suggestions for Gannan navel orange growers, hoping that Gannan's navel orange industry can have more scientific response measures and fewer blind attempts in the face of the Huanglongbing disaster.
Block the source: This means grasping the nursery stock barrier well in the early stage of industrial development and controlling the source of pathogens. New orchards should not carry pathogens, and orchards in epidemic areas should not add pathogens. To block the source, nursery stock must first be well managed. From the very beginning of orchard construction, great importance must be attached to the selection and purchase of nursery stock, and the introduction of pests and diseases must be prevented as much as possible. Nursery stock propagation must be carried out by qualified and eligible companies or individuals, implementing net-house cultivation and pathogen-free seedling raising.
Kill the vector: This means killing the intermediate vector and chief culprit that spreads the citrus Huanglongbing pathogen in the industrial base - the Asian citrus psyllid. This pest, which colludes with diseased trees like partners in crime, should be thoroughly eliminated. There are concentrated time periods (tender shoot stage, low-temperature period) when it can be controlled. Practice has proven that spraying pesticides in contiguous orchards at 6 key periods - winter, early spring orchard cleaning period, and the tender shoot stages of spring shoots, summer shoots, autumn shoots, and late autumn shoots - can effectively kill the Asian citrus psyllid.
Emphasize planning: Scientific planning and reasonable control of planting area. Reasonably return farmland to forest, and plant tall trees such as Chinese fir between different villages and towns as ecological isolation belts to hinder psyllid transmission. In addition, adjust the planting ratio of uniform varieties and increase the proportion of varieties with strong disease resistance. Form a navel orange planting system with reasonable area density and diversified variety types.
Emphasize technology: A change in thinking may find a breakthrough for industrial development. The urgent task now is to do deep and thorough work on "prevention." The government should organize unified prevention and control, use early diagnosis technology, biological control, and physical control technology to control the psyllid, while strengthening management, controlling environmental pH, and lowering the pH of irrigation water and soil to protect the citrus root system and improve disease resistance.
Article source: WeChat public account "Miller's Wheat Field," produced by the Harvest Research Office; please indicate the source when repostingRelated Articles
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