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Leaf Rust: What Can We Do?

leaf rust disease on coffee plants

Creative Commons photo by CIAT International Center for Tropical Agriculture

The coffee leaf rust (a.k.a. roya) outbreak that has been affecting huge swaths of coffee trees throughout Central America has been well documented by bloggers, the mainstream media and academics alike, and rightfully so. And in a new piece for the digital edition of the SCAA Specialty Coffee Chronicle, the group’s coffee science manager, Emma Bladyka, provides arguably the most comprehensive and well-researched piece to date.

Not only does the piece explore the current outbreak in an historical context, it also asks the important question of the industry, “What can we do?” Here’s an excerpt:

What can we do?

There is no quick solution to this problem. The outbreaks have already occurred, and are known to proliferate into multi-year events. The usual means of keeping the fungus at bay are no longer solutions to this problem. Since coffee rust spread over the producing regions of the world, fungicides have been used to lessen the outbreaks. Copper based fungicides are most common, but have short periods of effectiveness and applications must be timed carefully. In the end, these metallic fungicides can be detrimental to the environment and are limited in capacity to combat coffee rust.

There has been some research into a more biological or organic approach to combat the rust. Certain ‘hyperparasitic’ fungi (that are parasitic to parasites) have been identified in nature that prey on the coffee rust fungus (Muller et al. 2009). One such fungus, known as the ‘white halo’ fungus, has been getting lots of press lately. Scientifically, there is some evidence that this and possibly other microorganisms can reduce the viability of the rust (Jackson and others 2012;Vandermeer and others 2010Haddad and others 2009). However, there has never been any practical application suggested or implemented for this biological control in coffee. Unfortunately, at this juncture there is no real way to implement these additional microorganisms on a large agricultural scale. Nor has their ability been proven to eradicate large rust outbreaks, at the size and severity that the industry is currently faced with.

In the longer term, it will become critical to develop high quality resistant varieties. Kent was perhaps the first variety to show good resistance to coffee rust in India. However, this resistance was lost after about 10 years of exposure (Rodrigues and Eskes 2009). This phenomenon of gradually losing resistance has also been noticed in some C. iberica and C. canephora varieties. This led to the discovery that there were many ‘races’ of coffee rust and that new races could develop (Muller et al. 2009). Today, there are over 45 races identified, although a select few are likely responsible for most outbreaks (Fernandez and others 2012Rodrigues and Eskes 2009).  Currently, Catimors and Icatu show partial resistance to the rust, but lack many of the taste attributes desired by specialty coffee buyers. Unfortunately, the mechanism for resistance in coffee is not fully understood (Silva and others 2002Silva and others 2008Guerra-Guimares and others 2009). More research on how plants control the fungus will be necessary as the scientific community moves forward with identifying the specific genes that contribute to rust resistance.

For the full story, including information about an emergency summit addressing leaf rust mitigation taking place this April, visit the SCAA Specialty Coffee Chronicle digital edition.





In Nicaragua, there are many farms next to each other. On one side of the fence, lush green foliage with no rust, both shaded and less shaded, and the other side of the fence, no foliage, rust, cercospora, barren branches, with dried up black cherries. The difference was not just systemic fungicide such as ciproxizole, but also fertilization or the lack of. Many of these farms who borrowed money thinking coffee prices will be forever $3 dollars per pound of green beans borrowed money against future harvest to buy cars, build house, etc. could not afford fertilizer after coffee prices crashed, so application of fertilizer in june and september did not happen.

As for systemic fungicides that are applied as foliar spray, without leaves on the coffee trees, the foliar spray doesn’t work. At least the systemic fungicides penetrate the plant and kills the rust from within whereas the copper fungicides only work if in contact on the surface of the plant, so useless in rainy seasons. and the foliar spray has to be applied under the leaves, as rust infects the plant via the stomatas underneath the leaves

This is why good fertilizer practice is needed with urea initially is needed to cause a bloom of new leaves, then apply systemic fungicides so the fungicide is absorbed.

But this needs money $25 for 100 lbs of urea/npk and more for fungicides. biologic control at this point not possible on large geographic scale.

or we can all just drink more catimor, robusta, castillos.

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