How is Climate Effecting the Spread of Leaf Rust? by Kevin Stark

Editor’s Note: This is part of a continued series on our commitment to the Catracha Quality Project. Look for further articles and for the arrival of these coffees in the coming months. We have a few of these coffees available SPOT in both Oakland & Seattle

In recent blog posts (here and here), I shared some anecdotal experiences of coffee producers and other coffee professionals working around Marcala in Honduras. The attitude of people on the ground in Marcala was clear to me: climate change is not a distant threat, but the reality of everyday life. For many people, climate change is a reason—perhaps the reason—that farms are being threatened by disease, pests, storms, and, in particular, leaf rust. (find a related July 2015 contribution from Mariela Lagos here)

With the help of John Casazza, an agronomist working with Catracha Coffee and a consultant in sustainable agriculture development and food systems, I have been trying to answer one question: to what extent is roya a phenomenon of climate change?

Leaf rust has been a concern for coffee growers in Latin America for decades. Until recently, it was considered manageable through chemical application, especially at higher altitudes where rust caused relatively limited damage. This was true until a roya epidemic swept through Central and South America in 2012, but we’ll get to that in a moment.

First, what exactly is coffee rust? It is a particular kind of fungus, Hemileia vastatrix, an obligate parasite that consumes the living leaves of a coffee plant. It is an organism that multiplies by taking food from other organisms –  Arabica coffee in particular. Coffee leaf rust causes coffee branches to die and dramatically reduces the production of coffee.

Roya is a unique challenge for farmers. It has complex life cycle and the ability to travel in rivers, irrigation, rain and through the air (here is another summary from the SCAA).

There are a number of factors that contribute to the spread of the fungus. One main factor is financial. The economic argument goes like this (in short): when the price of coffee is low, coffee profitability is low and producers spend less money on fertilizers and pesticides for coffee plantations.

The drop in coffee prices was a presumed factor a rust epidemic in the late 1980s when support in the West for the International Coffee Organization’s quota system collapsed along with the Soviet Union and its client states. Roya spread through Colombia and Costa Rica, according to research published by Jacques Avelino in Journal of Food Security.

Avelino wrote that “all of the intense epidemics experienced during the last 37 years in Central America and Colombia were concurrent with low coffee profitability periods due to coffee price decline.” Rust is not new. In recent epidemics, Central and South America experienced a far larger and more harmful rust epidemic than what had been experienced before.

In Honduras, nearly 80,000 hectares were affected by an epidemic of coffee leaf rust between 2008 and 2013. The fungus decimated 10,000 farms completely, and nearly 20,000 farms saw a decrease of their coffee production by 50 percent, according to an assessment prepared for the United States Department of Agriculture in 2015. So, what happened?

Avelino and other researchers noted that rust epidemics are caused by a combination of economic, meteorological, and productivity factors. This time, something was very different. The growing season of 2012 and 2013 was almost a “perfect storm” with low coffee prices, decreased daily thermal temperature, an early rainy season interspersed with bright periods (see Fig 5 on page 306).

During this period, there was a reduction in the range of average temperatures in the coffee growing regions. Average low temperatures were higher, and average high temperatures were lower—a product of “climate variation” or the disruption of weather and rain patterns. Avelino wrote that this possibly led “to an increased number of days when the temperature fell within or close to the optimal range for coffee rust development.”

The research concluded that, in part, weather conditions caused the epidemic, and the experience could “be considered as a test in the face of global changes to come.” In other words—Avelino is not directly indicting climate change for the weather variability, but the spread of roya is predictive of future epidemics as the planet continues to warm. Here, we are venturing into interesting and complicated terrain, and an avenue of climate science that researchers are unceremoniously calling “event attribution.” It’s a new line of research; scientists are trying to determine if the effects of climate change are already happening, and what they might be.

A separate group of researchers are concerned that the media is attributing any strange weather event to climate change. In response, they are trying to describe very precisely the cause of extreme events and are publishing the results in the Bulletin of the American Meteorological Society. The attribution of extreme weather is an issue for coffee production and coffee quality, but perhaps more importantly it is an issue of food security. The vast majority of coffee producers are smallholders, and they depend on coffee as the primary source of income.

The science of extreme weather attribution can help the industry build resilience. While the current epidemic has been contained in Honduras, it is clear that roya is not going away, and that climate change will likely make it harder to control. Leaf rust is a constant threat to many of the Catracha farms I visited. But there are many factors—preventable factors—that contribute to the spread of rust. We cannot forget that the two main drivers are meteorological and financial. We need to recognize that the price paid for our morning cup directly relates to a farmer’s ability to protect their livelihood from cyclical devastation. Blaming climate change makes us feel powerless, but we are not. Our hard choices need to be made with eyes wide open.