Coffee leaf rust is one of the most serious diseases of coffee plants, especially Arabica (Coffea arabica). It primarily attacks the leaves but can also infect stems and berries. Infected trees lose their leaves, become weakened, produce lower yields, and in severe cases may die.
The disease was first reported in 1868 in Sri Lanka, where it reduced coffee production by as much as 75% within just ten years (1869–1878). By 1890, most coffee plantations there were abandoned and replaced with rubber and tea. From Sri Lanka the disease spread across Africa and other parts of Asia. By the mid-20th century it was present in nearly all coffee-growing countries in those two continents.
In 1970 coffee leaf rust appeared in the Americas, first in São Paulo state of Brazil, then spreading to other Brazilian states and countries such as Paraguay (1972), Nicaragua (1976), Colombia (1983), and Cuba (1985). In Paraná, Brazil during the 1973–1974 season, it cut yields by 34% even though 40% of the area was sprayed with fungicides. During 1989–1990, Colombia spent about USD 123 million spraying 250,000 ha of coffee.
Vietnam first recorded the disease in 1888, where it caused heavy losses. In the North, many French plantations were forced to replace Arabica with hardier “liberica” coffee. In Đắk Lắk during the 1940s the disease destroyed thousands of hectares of Arabica, leaving only about 60 ha; by 1957 all had been replaced with robusta coffee. In recent years, rust has also appeared on robusta—once thought to be resistant—with infection rates often around 50% and in some cases up to 70–85%.
Coffee leaf rust is caused by the fungus Hemileia vastatrix, which lives only on coffee. Early signs are small pale-yellow spots like tiny oil droplets on the underside of leaves. These spots enlarge and produce a fine orange-yellow powder of rust spores. Later the center turns whitish and finally brown, resembling a burn. These lesions may merge into large patches, causing the entire leaf to dry and drop. Severe infections defoliate trees and can kill them.
Temperature and rainfall strongly influence the disease. In Điện Biên it occurs year-round but peaks in March–April and again in September–November, with heavier autumn outbreaks. In Sơn La it peaks in September–November, occasionally in July–August. In the Central Highlands (Tây Nguyên), the rainy season drives the epidemic: on Arabica it starts in April–May, intensifies through July–August, and peaks in September–October. In a typical season nearly all trees can be infected and more than 90% of leaves show symptoms. On robusta three patterns are observed:
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About 10% of trees show an “Arabica-like” pattern with early, severe infections.
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Around 20% show very mild infections that begin early in the rainy season but only peak in December–January, with less than 40% of leaves affected.
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The majority (about 70%) develop rust from June, peak in November–January, with roughly 80% of leaves infected and a disease index of 2–15%.
Current control measures include planting resistant varieties, grafting, and chemical fungicides. In 1978 Vietnam’s Coffee Research Institute bred the Catimor Arabica cultivar, which has good resistance and is now widely planted. Another strategy is grafting high-yielding, rust-resistant clonal shoots onto infected trees.
For chemical control, fungicides such as Viben-C 50BTN, Tilt Super 300EC, Anvil 5SC, Dithane M-45 80WP, or Tilt 250EC can be sprayed as soon as the first signs appear, then 3–4 times during the season at intervals of 3–4 weeks, focusing on the undersides of leaves. In the rainy season it is advisable to add a sticking agent to improve adhesion.