According to an expert, coffee farmers should cultivate their crops in the shade to provide a favourable habitat for a parasite that can control the fungal disease leaf rust.
Tiny yellow spots on upper leaf surfaces and orange powdery lesions on the underside of leaves are signs of coffee leaf rust, which is caused by the fungus Hemileia vastatrix. Infected leaves gradually fall off, reducing crop yield and quality.
“Shade also provides a favourable habitat for the coffee leaf rust hyper-parasite, which we must exploit.” says Stockholm University’s Beyene Zewdie
However, a study conducted in Ethiopia on the sources of Arabica coffee, scientifically known as Coffee arabica, found that a natural enemy that grows on top of diseased leaves may be crucial in helping farmers combat the disease.
“The rust is a global threat for coffee production,” says Beyene Zewdie, a co-author of the study and post-doctoral researcher at Stockholm University’s Department of Ecology, Environment, and Plant Sciences. “It decreases coffee yields by up to 30%,” she adds.
Researchers looked at both the rust and a fungus that attacks it called Lecanicillium lecanii, according to a report published in Agriculture, Ecosystems and Environment this month (1 May). Observations were conducted in Southwestern Ethiopia during the wet and dry seasons from 2017 to 2019.
“We discovered that coffee leaf rust was more extreme during the dry season in two out of three years, while the hyperparasite [parasite whose host is also a parasite or L. lecanii] was more severe during the wet season,” the study says. “The hyperparasite was more prevalent under less intensive control, while the rust incidence increased with management intensity.”
According to Zewdie, the study could shed light on the relationship between rust and hyperparasite, as well as how to treat the two.