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T 4.04 Coffee Wilt Disease

Coffee Wilt Disease (CWD) disease was first observed in the Central African Republic in 1927, where it began to attack a lesser known species, Coffea excelsior. In the 1950s evidence emerged that arabica coffee might be susceptible. The coffee community really became aware of CWD during the 1997–98 conflict in the Democratic Republic of Congo (DRC). During the war, ripe and unripe beans from the DRC were trafficked into Uganda (J. Flood, 2009). This introduced a new disease to the Ugandan coffee crop and brought about devastation, with reports of up to 70% crop losses of robusta coffee. Strains of the disease now affect arabica coffee in Ethiopia and Tanzania, and surveys indicate it is now present in every growing region of Ethiopia (A. Girma et al., 2009). As the disease spreads to Tanzania, CWD is now considered the most severe threat to coffee production in Africa (J .M. Waller, M. Bigger and R. J. Hillocks, 2007).


How Infection Occurs

The way this disease spreads is not well known. However, just like leaf rust and coffee berry disease, it is the result of invasion by a fungal pathogen. The CWD pathogen is named Fusarium. Infected trees are killed outright within a period of 3 to 15 months, and younger plants can perish within weeks. The disease attacks the xylem, the vascular system that conducts fluid around the plant. Plants are unable to receive adequate water. Consequently, branches wilt and leaves become fragile and brittle and then fall off. Finally, the plant develops an irreversible dieback, which moves downward through the plant into the trunk and roots. 



Uprooted plants are usually burned and soil is rested for at least six months to allow it to recover. Fortunately, CWD has not been found to persist in soils after an outbreak. Whilst it is not known exactly how the disease spreads, it appears unable to traverse barriers of just a few hundred metres cut by farmers to quarantine affected areas (Delassus,