Coffee grey rust

Systematic position and nature of the pathogen: Hemileia coffeicola is an obligate parasitic fungus classified within the order Pucciniales (rust fungi). As a member of the Basidiomycota phylum, it is a highly specialized pathogen that has co-evolved with its host plants, primarily targeting specific species of the Coffea genus.

Diseases and host plants: This fungus is the causal agent of grey rust of coffee. Its primary host is Coffea arabica, though it can affect other coffee varieties. The disease is distinct from the more widespread coffee leaf rust caused by Hemileia vastatrix, as it manifests through specific grey or olive-colored sporulating lesions on the abaxial side of the coffee leaves.

Biology and life cycle: The life cycle is characterized by the production of urediniospores that act as the primary inoculant. The fungus infects the leaves by entering through the stomata. Once inside, it develops an extensive mycelial network that draws nutrients from the host tissues. Eventually, the fungus erupts through the stomata to produce new spores, enabling the rapid spread of the disease during favorable weather.

Conditions for development and harmfulness: The development of the pathogen is strongly favored by high atmospheric humidity and moderate temperatures ranging between 18°C and 24°C. The damage is severe as the disease leads to significant leaf drop. This defoliation impairs the tree’s photosynthetic capacity, resulting in poor fruit development, reduced yields, and long-term decline in plant vigor.

Protection and control measures: Controlling coffee grey rust involves a rigorous management strategy focused on prevention and chemical application:

• Selection and planting of coffee varieties that exhibit genetic resistance.
• Strategic pruning to improve airflow within the canopy and reduce leaf wetness duration.
• Application of copper-based fungicides or systemic triazole compounds during periods of high infection risk.
• Implementation of strict phytosanitary practices, including the removal of infected plant debris to limit the fungal inoculum.