Although Water Wise helps coffee farmers address the problem of water pollution, that isn’t the only problem affecting coffee farmers around the world.
Coffee rust — or coffee leaf rust — is a disease affecting coffee plants. It can be devastating to a coffee crop and menaces specialty coffee farming all around the world.
While it has probably been around since coffee was first grown, coffee rust first came to people’s attention in the 19th century, when it devastated coffee estates in Sri Lanka, which was then known as Ceylon and part of the British Empire.
From there it spread throughout Asia and Latin America. No coffee crop, it seems, is safe.
What is coffee rust?
The ‘rust’ is a parasitic fungus, known as Hemileia vastatrix, which feeds off the coffee plant. It usually appears as yellow or orange powdery marks on the underside of the leaves.
It spreads as spores, carried by wind or rain, which germinate when they land on coffee leaves. In fact, the fungus seems specifically to require the coffee leaves in order to germinate.
What does it do to the plant?
The disease affects the ability of the leaves to photosynthesize — that is, to convert light into energy for growth and survival. As a consequence, it depletes the leaves on the coffee plants and damages the coffee berries.
And because coffee rust kills off new leaves and shoots it, reduces the amount of coffee the plant can produce the following year, making it a big problem for the farmers.
How do we tackle it?
Some strains of coffee have better immunity to coffee rust than others and understanding the biology behind this is where the solution will probably be found.
In the meantime, the most effective treatment for coffee rust is metallic copper-based fungicides, which, as solutions go, is not nearly as sustainable as resistant strains of coffee.
But … what happened to Ceylon?
Coffee rust was so devastating to 19th century Ceylon that the coffee estates switched to tea farming instead.
Concerned about their lucrative trade in coffee, the British dispatched the investigative botanist Harry Marshall Ward to examine the coffee rust fungus. Although his findings, published in 1882, have been instrumental in fighting coffee rust, they came too late for the coffee estates of Sri Lanka.