When the fungus with the botanical name Hemileia Vastatrix is mentioned, shoulders slump. Roya, coffee leaf rust, is one of the worst and most feared fungal diseases on a coffee farm, and its outbreak has devastating consequences. It is responsible for millions in damages every year and can even destroy entire harvests. The fatal thing about it: coffee leaf rust can be spread by the wind and by humans. But first things first.
What is coffee leaf rust?
The coffee leaf rust, or "la roya" in Spanish, is caused by the fungus Hemileia Vastatrix and can be identified by orange pustules on the underside of a coffee plant's leaves. If a leaf has only a few of these round, rust-colored spots, it can continue to function more or less normally. However, if the environment promotes the development of Hemileia Vastatrix, it becomes difficult for the leaves to supply the plant with the nutrients it needs. Heavily infested leaves subsequently die off.
Although the fungus only attacks the coffee leaves, it damages the entire plant. Due to the lack of leaves, the coffee plant's ability to perform photosynthesis is limited, which means that in the year of infestation, due to a lack of nutrients, it can produce up to 50% fewer blossoms and, accordingly, fewer coffee cherries.
A distinction is made between primary and secondary loss
The primary loss refers to the harvest loss that occurs in the year of the first infestation. The defoliated coffee shrub can no longer provide the plant with sufficient nutrients, and the branches as well as the cherries cannot develop properly.
In the following year, we speak of secondary loss, which can be even more dramatic. After an outbreak in the year of the initial infestation, it may look as though the coffee plants are able to recover, since they can produce leaves again in the next season. However, damaged or dried-out, and thus dead, branches can no longer produce cherries. Studies in Central America have shown that primary loss can be up to 26%. For secondary loss, harvest losses are said to be as high as 36%.
Coffee leaf rust therefore disrupts the delicate balance of nutrient supply
Hemileia Vastatrix makes entire coffee-growing regions look like rows of skeletons and destroys the livelihoods of millions of coffee workers. As if the tragic extent of a coffee leaf rust outbreak weren't enough, the fungus also spreads with ease throughout the world.
During the 2012/13 and 2013/14 harvest seasons, the worst outbreak to date, which is also known as “The Big Rust,” global losses rose to 600 million dollars. Or to put it another way: over 300,000 people lost their jobs due to poor harvests.
How does coffee leaf rust spread?
The basic requirements for Roya can be explained using a triangle. For the optimal conditions for the fungus's development to be created, three elements are required:
- The right environment. Temperatures of an optimal 21-25°C promote the spread of coffee leaf rust, but it also copes brilliantly with temperatures of 15-28°C. If a hot and humid phase follows a rainy phase, the conditions are perfectly met. Coffee leaf rust needs water droplets on the leaves in order to germinate. So, if it is hot and dry, this is not a good environment for the development of Hemileia Vastatrix.
- The host. Coffea Arabica, in particular, is the sought-after host for the fungus. Coffea Canephora as well as Coffea Liberica and some varieties of Coffea Arabica are currently still resistant to coffee leaf rust.
- The pathogen. If the environment is right and the host is present, a pathogen is still required. If coffee leaf rust is present in the region, then the triangle is complete.
If coffee leaf rust is present in a region, it spreads incredibly quickly. The most common form of spread is the wind, which can carry the spores over many kilometers. But it is also spread by birds and insects, as well as by travelers on ships, trains, and even airplanes. At the beginning of the spread of Hemileia Vastatrix, the spores were carried by workers on their bodies and clothes and thus spread from one coffee-producing country to another.
On a single centimeter of an infected leaf, one can find up to 120,000 - 150,000 spores - an almost unimaginable number.
A reinforcing factor for the spread of coffee leaf rust is also the very low genetic diversity in Coffea Arabica. Most Arabica varieties can be traced back to the genes of Typica or Bourbon, which also means that they are all susceptible to the same diseases and fungi.
Hemileia Vastatrix has the ability to constantly adapt to new environments, comparable to influenza viruses in humans, and to mutate again and again. Many of the varieties that were still resistant up to 10 years ago are now susceptible to this life-threatening fungus. Higher temperatures, increased rainfall, extreme winds, and the increased mobility of humanity are some of the factors that have led to this.
Coffee leaf rust. The history. The world map.
The coffee world looked toward Asia with panicked eyes when every corner of the Indian Ocean basin was affected by coffee leaf rust in the 1950s. Hemileia Vastatrix continued its devastating path of conquest to West Africa and finally landed in the 1970s on the coffee farms spanning entire regions of Latin America. By 1990, it had spread to every one of the major coffee regions. However, it seemed that coffee leaf rust had been brought under control through adequate care and resistant varieties that many farmers started to plant - coffee leaf rust was, so to speak, a controllable nuisance.
Hemileia Vastatrix was already present in the primeval forests of Ethiopia before 1870, the place that is considered by many to be the cradle of the coffee plant. Back then, there were hundreds of Coffea species and varieties, and just as many diseases and fungi. But in harmony with nature and the way coffee production was handled and structured at the time, an infestation of one variety with the destructive fungus or another disease had no significant impact on the ecosystem and prevented a potential outbreak.
High biodiversity can stop coffee leaf rust. But in monocultures, it spreads at lightning speed.
From the tropically hot and humid weather of Ethiopia, coffee was brought to Yemen by the Ottomans and cultivated there on a large scale for the first time. Whether they brought coffee plants and thus also coffee leaf rust, or whether they only took seeds, is not known for sure. It is very possible that coffee leaf rust never came to Yemen, because Hemileia Vastatrix sticks to the coffee leaves and is not spread via seeds. In any case, the weather in Yemen was hot and dry and therefore not a good foundation for the development of coffee leaf rust and other diseases that cannot survive in this climate. The climate in Yemen was virtually a natural preventer of a coffee leaf rust outbreak, and so the devastating fungus remained undiscovered.
From Yemen, Coffea Arabica was spread throughout the world by the colonial powers of France, Great Britain, and Holland. Thus, the slumbering monster was given new breeding ground due to favorable weather conditions. The Dutch brought coffee from Yemen to India and from there around 1800 to Ceylon, known today as Sri Lanka. Soon after, the Dutch were driven out by the British, who immediately planted extensive coffee fields in order to make a lot of money from them.
Ceylon - a ticking time bomb
The first written record of coffee leaf rust was in 1861 in Sri Lanka (formerly Ceylon), where it could germinate optimally due to warm temperatures and heavy rainfall, destroying the entire coffee cultivation - by the end of 1880, most farmers had switched from growing coffee to tea (this, incidentally, is also the explanation for why Sri Lanka is a major tea nation today).
The large-scale coffee farms were all attacked by coffee leaf rust. Billions of the fungus's spores rose into the air and were distributed to large parts of the world by air currents, by people and ship transport, by birds and insects, and above all by the wind. By the 1950s, coffee leaf rust had arrived in the entire Indian Ocean basin - except for in Yemen. Coffee leaf rust contributed to the (temporary) collapse of coffee production in Asia and the Pacific. While these regions had accounted for ⅓ of total production at the beginning of the 19th century, 100 years later it was just 5%.
From the mid-1950s to the mid-1980s, the epidemic broke out in West Africa and was discovered for the first time in 1970 on a farm in Bahia, Brazil. From there, it continued to migrate and arrived in Central America in the 1970s. Discovered in Nicaragua in 1976, Hemileia Vastatrix had arrived in almost every small corner of Central America by the 90s.
The 3 phases of the coffee leaf rust outbreak
The history of coffee leaf rust is historically divided into three phases.
The first phase, the colonial phase, lasted from 1869 to approx. 1945 and included the first major coffee leaf rust outbreak in the Eastern Hemisphere. During this phase, the spread of the Hemileia Vastatrix fungus was driven by the mobility of the colonial powers and their exchange of enslaved people for harvest work.
The second phase, the developmentalist phase, describes the period from approx. 1950-1990, shaped by the Second World War as well as the Cold War. Global coffee trade was strongly regulated at this time by the International Coffee Agreement (ICA). In order to keep prices relatively high and stable, the ICA set export regulations for every country. States took on a greater role in the marketing of national coffee than they had in the colonial phase. For example, they supported farmers with technical and financial means and campaigned for social and political stability through various development projects.
Global distribution of the coffee rust, 1952. This map also reflects the global distribution of Arabica and Robusta coffee at the time. Most countries east of the line produced Robusta, while those west of the line produced Arabica. Coffee Areas of the World in Relation to Rust Disease. 1952. Foreign Agriculture 16:160.
Published in: Stuart McCook; John Vandermeer; Phytopathology® 2015, 105, 1164-1173.
Copyright © 2015 The American Phytopathological Society • DOI: 10.1094/PHYTO-04-15-0085-RVW
The third phase, also the neoliberal phase, denotes the time span from the end of the 1980s to the present. An insanely destructive series beginning in Colombia is known by the name The Big Rust, which reached its negative peak in the 2012/13 and 2013/14 harvest seasons in Central America.
In 2008, Colombia produced 31% less coffee than in the previous year. The epidemic spread further north, through Central America to Mexico, and then moved south again, finally reaching Peru and Ecuador in 2013/2014. The International Coffee Organization estimates that coffee production in Central America in the 2012/13 and 2013/14 harvest years cost more than 616 million dollars.
In contrast to previous outbreaks in past decades, the Big Rust was not triggered by a carrier being brought into an area where there had been no coffee leaf rust before. It was rather driven by extreme weather conditions, which had favored the development of the fungus.
The “Big Rust” in Latin America since 2008.
Published in: Stuart McCook; John Vandermeer; Phytopathology® 2015, 105, 1164-1173.
Copyright © 2015 The American Phytopathological Society • DOI: 10.1094/PHYTO-04-15-0085-RVW
Conclusion on coffee leaf rust
Hemileia Vastatrix is constantly adapting to new circumstances
The ecosystem and the economy are in constant change, and naturally so is coffee leaf rust, which, like influenza viruses, is constantly mutating. This means that living with Hemileia Vastatrix is always a snapshot in time and can change at any moment. For example, it is much hotter in higher-altitude regions these days than it was just a few years ago. Whereas our partners at Finca El Arbol used to have a daytime maximum of about 25°C around Easter, which is the hottest time of the year in Nicaragua, temperatures now climb to 35°C or higher.
Unstable stock market - catalyst for Roya
Added to this are the challenges of the stock market, which keeps prices unstable and makes long-term future planning impossible. If prices are too low and the coffee farmer cannot work in a cost-covering manner, let alone invest in renewing coffee plants, caring for the coffee farm, or fighting Hemileia Vastatrix or diseases, they must give up their farm. The land becomes wild, and coffee leaf rust spreads unchecked.
Roya makes coffee production more expensive
The control of Hemileia Vastatrix has made coffee production massively more expensive. With low prices, farmers cannot afford the control measures and must give up their farms, leave rural life, and build a new life somewhere else.
Roya shaped the coffee world as it is today
Coffee leaf rust has only marginally reduced the global supply of coffee, but it has shaped global trade in other ways. After 1900, the Dutch invested in the development of the resistant species Coffea Canephora, which soon stirred up the global coffee scene and now accounts for approx. 40% of coffee production. The plant, which was originally developed as an answer to coffee leaf rust, transformed and shaped the structure of global coffee production and consumption in the 20th century. But more on that another time.
Further reading
https://www.youtube.com/watch?v=gnPChFLHWA4
https://apsjournals.apsnet.org/doi/10.1094/PHYTO-04-15-0085-RVW#fig1
Stuart McCook, 2019, Coffee is not forever
