Unfortunately, coffee diseases have no natural predators,
and although fewer in number than the hordes of coffee pests, coffee
diseases are still largely chemically controlled. Although fungicides
are not as ecologically harmful as pesticides and herbicides, all
chemical treatments are expensive. The best control of coffee plant
diseases is careful quarantine, but that is not easy to enforce,
especially given the extent of international travel.
One of the worst coffee plant diseases is leaf rust (Hemileia
vastratrix). First reported in 1861 in Africa, by 1870 it had completely
wiped out the coffee industry of Ceylon, which resorted to tea-growing.
The virulent leaf rust quickly spread to every continent in the
coffee-growing world, although some countries have thus far been spared.
It is thought that leaf rust is spread by spores being carried on the
clothes of travelers from one country to another, particularly by people
working in the coffee trade. It is lethal for arabica trees, but robusta
is resistant to it.
A soil-inhabiting fungus causes another devastating
coffee disease, tracheomycosis, also know as vascular fungus, or coffee
wilt disease, to which robusta is more susceptible than arabica. In
fact, it was this disease that almost totally destroyed the Ivory
Coast's original coffee plantations of liberica trees in the 1940s,
after which time the Ivory Coast became a large grower of robusta and
the developer of arabusta. In the Democratic Republic of Congo, coffee
production has fallen consistently since 1994, due to this disease and
internal tribal warfare affecting the same regions.
Another very serious disease affecting arabica trees is
coffee berry disease (colletotrichum coffeanum). Also called brown
blight and red blister, coffee berry disease is a fungus, first
identified in Kenya in the 1920s, which may attack a coffee tree in the
wake of its carrier, the antestia bug. Rain splashes can also spread
residues of the disease, even those from a previous crop. The disease
attacks the coffee cherries, causing maximum damage to green cherries,
turning them dark with decay. Fungicidal sprays are successful in
controlling coffee berry disease only to some extent, and therefore this
disease is the subject of much hybridization research.
Hybridization can certainly offer hope for conquering
many coffee enemies, as one variety, susceptible to a particular pest or
disease, is crossed with another variety which is naturally resistant.
Although crossbreeding may eventually see the disappearance of some
coffee diseases (thus far what is seen is more the disappearance of
flavor), there is a category of coffee enemy to which all varieties are
vulnerable; these are the natural disasters that plague many