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Coffee is susceptible to a large range of pathogens.
Even wild arabica growing in the cloud forests of Ethiopia is susceptible to coffee leaf rust, however, the shaded forest environment and cool climate of this region is less favourable to the growth of leaf rust.
Coffee leaf rust (CLR) is caused by the fungus called Hemileia vastatrix
CLR infects the undersides of the leaves of coffee plants where it produces large, rust coloured colonies of uredosori — a nice way of saying pustule.
Leaf rust produces spores at a rate 2000 fold higher in temperatures between 22-27°C temperature range compared with an 18-23°C temperature range.
There is a direct link between low coffee prices and outbreaks of pests and disease: ‘All the intense epidemics experienced during the last 37 years in Central America and Colombia were concurrent with low coffee profitability periods due to coffee price declines’ (Avelino et al., 2016)
There are not coffee varieties in production that are completely immune to coffee leaf rust.
Most conventional and organic treatments are copper based foliar sprays which build up as a pollutant in the soil during prolonged use.
Dr. Jacques Avelino has shown that optimal plant nutrition via controlled fertilisation has more benefit to reducing infestation of rust than the use of fungicides.
Infected cherries develop dark lesions which begin to release spores from small blooms coming out of the centre of the lesions known as acervuli. The disease causes the fruit to drop before it is ripe and when no controls are implemented, it can result in crop losses of 70-80%.
Robusta appears to be totally resistant but no arabica coffee genotypes have been shown to be totally resistant to CBD. Certain arabica cultivars and hybrids such as Ruiru 11 and Sudan Rume have good resistance to CBD.
Coffee Wilt disease (CWD) attacks the xylem of the plant.