Originally published, October 8, 2012
By Gabriela Cordon
“Coffee growers reiterated they face the most severe rust outbreak in recent years”, El Mundo Digital, El Salvador.
According to Freddy Wellman, a plant pathologist whose major work was on coffee diseases, the Coffea Arabica is subject to more than 40 diseases due to different factors. About three years ago, rust began to appear on the front page of many coffee media, and coffee organizations, mostly from Central American countries, have begun to take action, while production reduction is being anticipated by 20 to 40 percent.
But, what is it that makes coffee rust more prevalent now than before? In 1952 Wellman had recommended that “given the imminent danger of invasion of the disease, preventive measures should be taken and prepare plans to fight it when needed“. Is it now more aggressive, of have new strains developed? What can coffee growers do to prevent this disease, which is also called “oriental leaf disease”? Is it easier to manage it in organic or traditional coffee production? Well, let´s find out.
The birth of coffee and its worst diseases
In 1879, coffee rust was first detected in the island of Ceylon, nowadays Sri Lanka. British mycologist Berkeley dedicated his expertise to study this fungus, and presented a description of its development, naming it as Hemileia Vastatrix. After the rapid infestation of the coffee plantations, there was no other solution but to stop the coffee cultivation of the major world producer. Drinking habits of the British people were also affected. They started growing and drinking tea(1).
Its origin was uncertain since the island was not close to Central and East Africa, where the birth of coffee was and its major diversification. But there was an explanation to that: the plant and the fungus coexistence were related to its genetic resistance and the fungus virulence(2). The species grown in Ceylon were highly sensible to the disease which made them believe it was not from the zone.
The theory is then that the fungus was introduced to the island by infected plants brought from Africa. Wellman reported in his studies that perhaps the origin of rust was in fact in 1861, near Lake Victoria, in East Africa, where a British explorer had noticed an outbreak on wild coffee plants extremely rare because of their same nature and thus, left unattended for years.
It propagated rapidly throughout Asia, but it was not until 1960 that it was present in some regions in East Africa, and ten years later it reached America. Some believe it was transported by the trade winds, but others blame clothes or vegetal material.
The oriental coffee leaf is a disease caused by the fungus Hemileia Vastatrix. Its main way of multiplication is the uredospore (A dikaryotic spore formed in a spore cluster by certain rust fungi(3)). It is a parasite that attacks leaves of the Coffea gender’s species. The Arabica specie is the most attacked. The fungus enters through stomas of the lower face leaf. The first symptom is yellow spots that later will produce an orange uredospore. The upper face leaf will show chlorotic spots and then they will turn necrotic.
Phases of the disease could be identified as dissemination, germination (which is the beginning of the infection, but it is not yet established), and the penetration of the fungus through the stomas of the leaf, where the infection takes place. The shorter the period from the germination to the appearance of the first yellow spots, the faster the cycle will repeat to create an epidemic.
What are the ideal conditions for this fungus to work faster? Liquid water present in all the process until the penetration of the stomas. Experts estimated that 0.3 inches of rain are just enough to liberate uredospore, which will travel small to medium distance through spattered rain drops or insects(4). If the spores are too disseminated, the infection will not take place. It is required about 15-30 spores per square meter to reach the optimum contamination.
Combined ingredients are temperature from 22° to 23° C, and obscurity. Penetration of the stomas need no less than six hours, and nonstop rain from 24 to 48 hours are just the ideal. But also mature leaves are needed because the stomas will be in better conditions for the fungus. Stress can also favor the process such as high presence of fruit or intense luminosity before the fungus is deposited(5).
Epidemiology studies made in Mesoamerica confirmed that defoliation is a key control factor since older leaves will keep inoculum residues which will survive the dry season and will initiate a rapid infection with the first rains the following year.
Growers in action
Grower’s contribution is basically prevention. Back in the 90’s, it was studied that the infection would be less aggressive in higher altitudes (at 1,110 MASL 16% of young leaves were infected vs. 32% at 460 MASL). That is way experts concluded that higher altitudes could start later with a prevention plan(6). But nowadays, farms at 1,400 MASL reported higher infections. Perhaps it was due to the combination of constant heavy rain cycles and the biannual productivity of coffee.
According to a study made in Mexico and Guatemala by a group of professionals, 50% of the variability of the disease was related to the amount of production and thus, to the biannual cycle of coffee. Nevertheless, a proper control of rust is vital and crucial even if it is useless during the low production period. One thing is certain: chemical control is needed. What varies is the usage of cupper based or systemic products.
Cupper based products were rapidly applied basically because of its low cost and its proven effectiveness in other countries affected. Studies concluded that three bimonthly applications of a copper oxychloride based product, with half of metallic copper and 3.5 Kg per hectare dose were efficient to control the infection. These products are approved by Organic certifications since they stay in the leaves and do not penetrate them, preventing its contamination for human consumption. Instead, they do contaminate the environment, because copper is a heavy metal that pollutes water and soil.
Systemic curative products, for leaves or soil application, were also studied, specially the family of the triazoles. The issue with this type of products is that they are highly effective, but also highly expensive.
Additionally, they do not contaminate the environment since triazoles are degraded. However, Organic certifications do not approve them because they do penetrate the plant and therefore they are not ideal for human consumption. Depending on the stage of the infection, copper based products may not be recommended.
Again the effectiveness of the control and curative processes will be related to how efficiently growers can execute recommendations of experts and field technicians. All standardized criteria should be used with a common sense and attention to differences in their own farms. More and more variables might be added, and they will have to adjust them with their best of knowledge. One of those is unpredictable weather patterns affected by global warming. As experts stated in the 1990’s, coffee rust is not a myth any more, but a reality growers have to deal with in order to continue coffee quality production.
1 Rayner, R.W (1972) Micología, historia y biología de la roya del cafeto. Publicación Miscelanea No. 94. IICA, Turrialba, Costa Rica.
2 Jacques Avelino, CIRAD-CP-IICA-PROMECAFE; Raoul Mulier, ASIC; Albertus Eskes, CIRAD-CP; Rodney Santacreo, IHCAFE (Honduras) and Francisco Holguín, INIFAP. The coffee rust: myth and reality. Chapter 6, Page 193-196.
3 Dictionary of Botany. http://botanydictionary.org/uredospore.html
4 Jacques Avelino, CIRAD-CP-IICA-PROMECAFE; Raoul Mulier, ASIC; Albertus Eskes, CIRAD-CP; Rodney Santacreo, IHCAFE (Honduras) and Francisco Holguín, INIFAP. The coffee rust: myth and reality. Chapter 6, Page 205.
5 Idem. Page 206.
6 Idem, Page 212.