Leaf Rust, or roya, as it is called in Spanish, is a naturally occurring fungus in coffee fields. It can be held in check when the fields are kept in ecological balance. But during the 2012–2013 growing season, with peaks of abnormally high temperatures and prolonged periods of excessive humidity combined with vulnerable soils and trees due to the lack of investment and healthy agricultural practices, the orange fungus spread like wildfire. Once the fungus hit its tipping point, it spread across Central America, affecting between 15 and 85 per cent of yields, depending on local conditions. Roya attacks the leaves, the primary source of photosynthesis of the coffee plant, which not only affects ripening of the current-season cherries, but can also cause the flowers of the following season to drop, and depending on the intensity of the infestation can kill a branch or the entire tree—thus affecting the current harvest and harvest yields for many years to come…

For the complete Dominion article, check out Coffee Rust Crisis