Monday, February 11, 2013

Bourbon Apocalypse

Roya (Coffee Leaf Rust) a.k.a. Hemileia Vastatrix is this year's Central American coffee farmers’ # 1 enemy. It’s a fungus that causes coffee leaves to fall, starving out the plant and drastically reducing cherry production. Roya is the most damaging, widespread coffee disease, found everywhere except for Hawaii. We had never seen such a severe attack in El Salvador as we’re seeing now: thousands of acres of what used to be beautiful plants are now leafless, dry twigs. 

You can recognize the plague by the light-orange powdery lesions (spots) on the underside of infected leaves, shown on the photo above. A few spots on a leaf can cause it to fall and die.
Roya spreads over large distances mainly by wind, landing on coffee leaves and penetrating through the ‘skin’ into the leaves’ internal photosynthesis factory where it sucks out nutrients. Eventually the fungus produces new spores on infected leaves (one lesion produces 4 to 6 spore crops over a 3–5 month period releasing 300,000 to 400,000 spores) and continues to spread.

Water is necessary for disease development, with rain playing a vital part by providing moisture for spore germination and then aiding in dispersal through rain splash. Seasonal variation in disease incidence is mostly due to variation in rainfall patterns. Therefore, the spread of this fungus is usually limited to the rainy season though the disease is often evident in the forthcoming dry season, since incubation time between infection and lesion development is around 3 to 6 weeks. 

In the past El Salvador had well defined wet and dry seasons, though lately we’re seeing quite a few unexpected showers during harvest season, allowing the plague to keep spreading all year round. Last month we visited a farm that looked incredibly healthy and when we returned 3 weeks later, leaf rust was everywhere, leaving barely any leaves standing. Added to this, roya used to be considered a threat only for low altitude coffee, however in recent years we have observed the fungus spread to Strictly High Growth coffee zones. 
Roya has short and long term consequences. To start, it reduces the photosynthetic capacity of infected leaves and at high infection levels causes leaves to fall, leading to less vegetative growth and smaller berry size. How?

A starving plant has no energy to produce tasty beans! Think of a roya infected plant as a smoker running a marathon. Having less leaves is like having reduced lung capacity, midway through the race you’ll run out of steam. A plant with very few leaves is low on energy and has to decide: should I use my remaining energy to make baby beans or should I make leaves so I can survive? 
Starving plants think of themselves first, they don’t produce beans and if they had already before the disease hit, they’ll abandon them mid-harvest (arrested berry development!): the beans stop receiving enough nutrients to grow and they’ll just hang on the tree, staying small and green - never becoming bright red cherries.

Hemileia vastatrix spreads, the leaves fall, the plant starves = no beans.
Leaf rust also affects next year’s harvest: shoots and roots starve and consequently dieback, thus reducing the quantity of nodes on which coffee beans will develop the following year. Since next season’s production of beans takes place on plant matter created this year, the tip and shoot dieback caused by Hemileia vastatrix will greatly reduce next season’s yield. Plants weakened by rust are also more vulnerable to other diseases, such as cercospora and anthracnose. 
Diseased plantation above vs healthier farm below

There are other reasons why El Salvador is especially susceptible to roya. In other countries, after little more than two decade, plants are cut down and new ones are planted. (New plants tend to produce more; as plants age they become weak and vulnerable to diseases). Here in El Salvador we barely renovate our plantations; it’s common to see 70 year old plants still producing coffee. During the 80s, while other producer countries were busy modernizing their plantations with highly productive, disease resistant hybrids, we were in the middle of our civil war, so now we find ourselves with delicious Old World Bourbons, which though great in a cup, are too delicate to resist roya. Not only are many of our plants old and feeble, they’re also non-resistant varieties.

It’s quite unlikely we will eradicate roya with fungicides, and excessive use causes more harm than good, by also killing off roya’s natural predators such as the white halo fungus and generally disrupting the ecosystem’s balance. Some agronomists are of the opinion that roya has now effectively escaped its natural controls; having vast areas of coffee monoculture certainly does not help contain the plague.

Though early intervention decreases the spread of the disease, this can be frustrating because even if you combat the fungus in your own plantation with effective land management and fungicides, your neighbor might not, due to carelessness or lack of funds. The photo above is from a farm that has been basically abandoned to plagues, not only leaf rust but also cercospora and anthracnose. This mismanaged farm provides excellent accommodations for plagues, helping them spread to neighboring farms.
Top side of roya infected leaves
In conclusion, due to irregular rainfall, roya now has a longer period to spread and because of either climate change or evolution of the plague, it now reaches higher altitudes it hadn’t affected before. Is this the end of Bourbon predominance in El Salvador? Will this turn out to be a passing phase or will roya continue until it decimates our plants? Should we start ripping out our Bourbons and start planting less flavorsome, more resistant hybrid varieties? This is a tough choice facing farmers now, and one which could completely alter El Salvador’s mountain landscape.

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