Coffee leaf rust, or la Roya in Spanish is a terrifying disease affecting most coffee producing countries around the world. CLR is caused by a fungus called Hemileia vastatrix, which is believed to have evolved over millions of years alongside flowering plants in present day Ethiopia.
Rust fungi are actually parasites meaning they need a host to survive, the microscopic spores enter through the leaf pores where they germinate and colonize the host cells of the leaf. They kill these host cells along with the leaves and begin producing the next series of spores. The new spores exit the leaf primarily due to rain. Once they’re free they can be carried by the wind, animals, or most likely humans. Once the spores arrive at a new host, the infection starts all over again.
La Roya is ancient but it has only started affecting coffee on a wide scale in the last 150 years. The first recorded instance was in modern day Sri Lanka in the 1870s. Ceylon as it was known then, was the world’s third largest coffee producer. Coffee Leaf Rust decimated the monoculture-style large plantations which were owned by the British, before it traveled in the wind or on people all the way to the Philippines and Hawaii within 30 years, drastically restructuring coffee production around the world.
CLR’s main effect on the coffee plant is unprecedented defoliation. Since the tree loses so many leaves, it can’t properly photosynthesize, greatly affecting both quantity and quality of the harvest. CLR thrives in single coffee cultivars which lack genetic variety and strongly prefers Arabica over Robusta since the latter is thought to be CLR-Resistant.
In the 1950s La Roya flared up in West Africa along with the expansion of coffee production in this region but since the area produced mostly Robusta varietals, the economic impact was mitigated. In the 1970s CLR reached the Americas and it started to spread throughout the coffee growing regions, it was historically kept at bay through chemical application and pruning practices.
At the beginning of 2008 parts of Latin America experienced a severe cluster of outbreaks now known as “the big rust” and by 2012, Coffee Leaf Rust incidence was recorded across Central America, the Caribbean, Ecuador, Peru, and Mexico on a level not seen since Ceylon. Honduras probably the most affected country, is still feeling the effects of this epidemic.
Fungicides have for a long time been the most effective coffee leaf rust treatment but in many instances the disease develops a resistance to the spray. With consumers demanding the avoidance of chemical application, coffee producers sometimes find themselves with a lose-lose proposition, though a lot of them are turning to a diversification approach to combat Roya.
This approach can mean applying agroforestry principals in farms which involve planting multiple crops or varieties of the same crop and growing shade trees, which in turn produce fruit or become firewood and timber. Thorough pruning and shade management are key since it’s been found that stressors such as too much sunlight and a lack of nitrogen in the soil can increase coffee’s susceptibility to the rust fungus.
Unfortunately, the Coffee Leaf Rust epidemic will most likely continue to wreak havoc. Average global temperatures have increased by around 1.8° F with accompanying natural changes in the oceans and atmosphere. This rise in temperature has allowed la Roya to attack higher altitude coffee. Ten years ago CLR incidence was barely detected over 1000 meters above sea level, it has now been found at 1,800 MASL. Climate change has made most rain cycles erratic with shifting rain patterns and extreme storms. Higher temperatures and excessive wetness are perfect conditions for a Roya outbreak.
Rust-resistant coffee varieties have been in use for over 100 years. one of the earliest known selections in Mysore, India came from a Typica tree that showed a remarkable ability to withstand the fungus. They named this varietal Kent and it became popular in India, Uganda, Tanzania and Kenya. CLR resistant varieties are the result of years of work by coffee research institutes, historically these quasi-state institutions have shared, disseminated knowledge, and provided technical support to coffee producers.
CLR resistant varietals were not known for their quality until 2005, when CENICAFE, one of such institutes introduced the largely popular Castillo varietal. This cultivar is now the most commonly grown plant in Colombia, thanks in part to heavy marketing, national taste competition victories, and subsidized seed pricing. In fact, by 2015, Colombia had more than 60% of its total coffee area planted with Coffee Leaf Rust resistant varieties.
Another victory in the battle against la Roya are the new F1 Hybrids, which show a lot of promise. Some of these hybrids have demonstrated resistance to Coffee Leaf Rust, have a superior flavor, can be grown in shaded conditions, and perform well at low altitudes.
The F1 hybrids are not genetically modified, instead, they are the result of hybridizations between wild Ethiopian or Sudanese coffee plants and commercial varieties, however, they are expensive and cannot be reproduced by seeds. They are reproduced in labs by in vitro technique and multiplied in specialized nurseries making them out of reach for most coffee farmers.
La Roya seems to me bigger than a disease, something which cannot be eradicated, a problem that cannot be solved. Sort of like Climate Change, where we have passed the point of no return.
Rather, we should be using a diverse suite of strategies to combat and mitigate its impact.
It's been shown that a coffee producer with the right resources can learn to cope with Roya either by being able to replant resistant varietals, hire labor to monitor and treat the disease, or being able to acquire knowledge on Coffee Leaf Rust treatment. There's even studies that show a correlation between financial instability and Roya epidemics, CLR is bigger than the fungus.
So what can you do as a consumer? Make sure your coffee supply chain is short so that most of the benefit of your purchase stays at origin and go to the coffee producers. Support coffee farms using agroforestry principals including planting multiple cultivars. Lastly, try rust resistant varietals, you'll see they're just as delicious. Until then, Enjoy!
Photos from: https://hdoa.hawaii.gov/pi/files/2020/12/NPA-20-03-Coffee-leaf-rust-12-20.pdf Department of Agriculture State of Hawaii