Coffee Leaf-Rust Risk — Environment Index

Rust-Risk Calendar — Conditions Conducive to Infection

Cell = mean nightly infection-risk class within the dekad, from a temperature × leaf-wetness-duration matrix. This measures weather conducive to infection — not confirmed disease. Actual outbreaks also depend on host susceptibility (species, variety) and crop load — surfaced as realized-risk modifiers below — plus pathogen presence. Absolute scale (not deviation) so chronically-humid origins read at their true level and all origins are cross-comparable.

Robusta vs. arabica — read these origins differently. Leaf rust (Hemileia vastatrix) overwhelmingly attacks arabica. Robusta (Coffea canephora) — Vietnam, Indonesia, and Brazil's Espírito Santo conilon — carries strong genetic resistance: not immune, but highly conducive weather that would be very dangerous in arabica typically passes with limited damage. Treat High/Extreme readings at robusta origins as a weather signal, not an outbreak warning. The arabica origins — Colombia, Central America, Ethiopia, and Brazil Sul de Minas / Cerrado — are where conducive conditions translate into real crop and price risk.

Rust-Risk Class · HEADLINE (0 Low → 3 Extreme)

Nightly class from the infection matrix below, averaged over the dekad's nights. Hover for value; dotted line marks the start of the forecast window.

Decomposed Inputs — What's Driving the Risk

Leaf-Wetness Duration

Longest continuous wet spell per night (hours, dew-point depression < 2°C ≈ RH ≥ 90%). The moisture input — falls during drought.

Mean Night Temperature · LEADING INDICATOR

Average overnight temperature (°C). Germination peaks near 21°C, but infection stays conducive as nights cool toward ~13°C; only very cold (< 13°C) or hot (> 30°C) nights cap risk.

Latest Dekad by Origin

Host, Load & Husbandry Context — Realized-Risk Modifiers

The calendar above is weather conduciveness. Whether conducive weather becomes disease depends on host susceptibility (species & variety), crop load, and husbandry — independent modifiers shown here so equal conduciveness can be read as different realized risk across origins. Bearing year is derived from CONAB arabica production history.

Brazil S. Minas · Cerrado susceptibility: High — susceptible arabica (Mundo Novo / Catuaí dominant) · 2026 is an ‘on’ year (high-load ↑ 44.1M bags, +23% vs prior) → realized risk amplified
Brazil Espírito Santo susceptibility: Low — conilon (C. canephora) — strong resistance; only weakly biennial
Central America susceptibility: High (eroding resistance) — post-2012 renovation to resistant catimores (Lempira, Marsellesa) is partial and resistance has broken in places (Lempira, Honduras 2017)
Colombia susceptibility: Low–Moderate — majority rust-resistant Castillo / Cenicafé varieties since the post-2008 renovation → conduciveness overstates realized risk
Ethiopia susceptibility: Variable — heirloom landraces with diverse, mixed resistance; mostly low-input garden / forest systems
Indonesia (Lampung) susceptibility: Low — robusta (C. canephora) — strong resistance
Vietnam (C. Highlands) susceptibility: Low — robusta (C. canephora) — strong resistance

Input-affordability pressure (husbandry — leads by ~1 season). Nutrition and fungicide a grower could afford a season ago set this crop's resilience; today's affordability leads the next crop's vulnerability. Affordability = coffee price ÷ fertilizer basket (urea + potash), percentile vs history. FX-adjusted for Brazil only (v1); other origins read the global USD-basis complex.

Input-Affordability — 36-Month Trajectory

Monthly affordability percentile vs full history (higher = inputs more affordable → husbandry supported). A sustained fall = rising input-affordability pressure, building vulnerability into the next crop (~1-season lead). Dotted line = median.

Arabica complex KC ÷ fertilizer husbandry window (lagged 6mo, 2025-11): 100 pctile affordability → well-resourced crop — current 51 pctile, souring (-45% vs 6–12 mo prior); souring now → vulnerability building into the next crop.
Robusta complex RC ÷ fertilizer husbandry window (lagged 6mo, 2025-11): 93 pctile affordability → well-resourced crop — current 55 pctile, souring (-42% vs 6–12 mo prior); souring now → vulnerability building into the next crop.
Brazil FX overlay BRL/USD 5.06 vs 5.55 a year ago — a firmer BRL is dampening the FX tailwind Brazilian growers had.

Infection-risk matrix (temperature × leaf-wetness duration)

Engine: for each origin, hourly 2 m temperature & dew point are sampled at 3 representative points. Per local night (18:00–06:00) the longest continuous wet spell (dew-point depression < 2°C) gives leaf-wetness duration (LWD); its mean temperature and LWD are looked up in the rust infection matrix → a nightly class (Low/Medium/High/Extreme). Dekad cell = mean class over the dekad's nights; the table also reports the share of nights reaching High+. Cardinal temperatures and the ~6 h wetness threshold follow de Jong 1987 / Bebber 2016. Data: Open-Meteo (recent actuals + 14-day forecast). Generated 2026-06-17.

Calibration: the matrix reflects the two-stage thermal biology of infection — urediospores germinate near the warm evening peak (optimum ≈21°C) but appressorium formation and stomatal entry proceed optimally as the canopy cools overnight toward ~11–16°C, so cool highland nights are conducive (not protective) once a wet spell has started. Risk floors at the ~13°C germination minimum and is suppressed above 30°C; ~6 h continuous wetness ≈ one infection opportunity. Thresholds follow de Jong 1987 / Bebber 2016 and will be refined against operational warning systems (e.g. Pozza et al. 2021). Read relative differences across origins and dekads as the primary signal.

Realized-risk modifiers: host susceptibility (species & variety), Brazil's bearing year, and input-affordability pressure (the husbandry lever, leading by ~1 season) are surfaced in the Host, Load & Husbandry Context section above — robusta origins and resistant-variety arabica (e.g. Colombia's Castillo) carry conducive weather with less realized disease, a high-load arabica "on" year amplifies it, and affordability a season ago sets how well-defended the current crop is. Still deferred: an observed-incidence feed (remote-sensing / field reports) to confirm where conducive weather actually became disease — the validation layer that would let these modifiers be combined rather than read side-by-side.

References: Bebber et al. (2016) Phil. Trans. R. Soc. B; Jong et al. (1987) Neth. J. Plant Pathol.; Yan & Hunt (1999) Ann. Bot.; Avelino et al. (2015) Food Security; Pozza et al. (2021) Agronomy.