Rust is diagnosed by eye, by turning over the lower leaves. The lesions sit on the underside of the blade: without this gesture, nothing is seen.

Surveillance, for its part, relies on incidence surveys made on sampled trees. Incidence is the share of leaves carrying at least one lesion, expressed in classes rather than as an exact value. IHCAFE thus publishes national incidences by class of farm (5-10%, 10-15%, more than 15%) and by department.

This figure is used to decide, not just to describe. Brazil recommends contact fungicides below 5% incidence and systemic ones above it (Zambolim, 2016), with a visual scoring grid applied by a trained eye.

Knowing which race is attacking, on the other hand, takes a laboratory. Typing is not done in the field: samples go to the CIFC to be inoculated onto the differential series, like the eighteen Peruvian samples of 2024.

A recent tool shifts the moment of sorting. Since 2025, breeding has had low-cost genetic markers for rust resistance, developed by WCR with Cenicafé and the USDA. They make it possible to sort seedlings before planting them, and so to read what a young plant carries without waiting to see how it behaves in the field.

USDA FAS, Coffee Annual Honduras (May 2025); BSPP 2022, p. 17; Quispe-Apaza et al. 2024; WCR, 2025 Annual Report (05/14/2026)

Warning models are recent. Bebber et al. (2016) built a mechanistic model of germination and infection from canopy temperature and leaf wetness duration, calibrated on climate reanalyses; daily risk is correlated with canopy surface water (r = 0.87). In Nicaragua, the CAFENICA association of cooperatives launched an early warning system in 2018 and distributes climate data with CIAT to decide on treatments; the ExpeRoya model, built by Cirad in the Procagica project, forecasts epidemics in Central America and the Dominican Republic with IICA (Motisi et al., 2022).

For the berry borer, the 30-tree sampling method introduced in Hawaii in 2012 gives the percentage of infested cherries, the position of the insect in the berry (still in the pulp, and so reachable by a treatment, or already in the bean) and the foci; alcohol traps (ethanol-methanol, 15 traps per hectare in the Ugandan protocol) are used to monitor flights and for mass trapping.

For the leaf miner, one pheromone trap per four hectares, and aerial imaging and ground photogrammetry systems under development. For coffee wilt disease and root rots, only destructive diagnosis exists (cutting the trunk, digging up roots).

Bebber et al. 2016; BSPP 2022, p. 15 (CAFENICA 2018; Motisi et al. 2022); Lee et al., “Economic Benefits from Managing Coffee Berry Borer in Hawaii” (2023); UCDA 2019, p. 77; Insects 12 (2021), review of Leucoptera coffeella