Pathogen Pressure Forecast.
Pathogen Pressure Forecast
Environmental conditions favor different pathogens. This tool flags which are most likely given yours.
How this works
Most agricultural pathogens have well-documented environmental drivers. Botrytis (gray mold) thrives at high humidity and cool temperatures with still air. Spider mites multiply in hot, dry, low-airflow conditions. Pythium colonizes warm, oxygen-poor root zones. The conditions don't cause disease (pathogens still need to be present), but they create the windows in which infections take hold.
The pressure index above is a 0-1 score combining the environmental drivers for each pathogen. It is advisory, not diagnostic. A high botrytis score doesn't mean you have botrytis; it means conditions favor it if spores are present. Inspecting plants and adjusting environment proactively is the use case.
How the score is built
Each pest or disease gets a 0 to 1 index from a fixed set of weighted environmental drivers, capped at 1. The weights are set by hand from the published favorable-condition ranges in the table above; they are not fitted to field outbreak data, and the index has not been validated against observed disease incidence. Treat it as a conditions indicator (are the drivers lined up?), not a probability that the organism is present or a trigger for treatment. Inputs the model does not see, such as inoculum, crop susceptibility, cultivar, and canopy density, matter as much as the ones it does.
| Organism | Drivers and weights (summed, then capped at 1) |
|---|---|
| Botrytis | RH at or above 65%: +0.40 (ramps in from 55%). Air 55 to 72°F: +0.25 (fades out by 80°F). Still air: up to +0.20. Leaf wetness: up to +0.15. |
| Powdery mildew | RH 55 to 90%: +0.35 (ramps in from 45%). Air 60 to 80°F: +0.25 (ramps 50 to 60, fades 80 to 90). Still air: up to +0.20. Leaf wetness: up to +0.20. |
| Spider mites | Air 85 to 95°F: +0.40 (ramps in from 80, fades out by 100). RH below 40%: up to +0.35 (partial credit below 50). Still air: up to +0.25. |
| Pythium | Root temperature above 78°F: +0.50 (ramps in from 72). Saturated substrate: up to +0.40. RH above 75%: up to +0.10. |
| Fusarium | Root temperature above 75°F: up to +0.40 (full at 85). RH above 70%: up to +0.30. Saturated substrate: up to +0.30. |
| Septoria | RH above 70%: up to +0.30. Air 60 to 80°F: +0.25. Leaf wetness: up to +0.45. |
| Damping-off | Cold root zone (below 65°F): up to +0.30. RH above 75%: up to +0.25. Saturated substrate: up to +0.25. Still air: up to +0.20. |
Airflow, leaf wetness, and substrate are the coarse choices in the form, mapped to 0, 0.33 or 0.5, 0.67, and 1. The severity labels (Low under 0.30, Moderate to 0.60, High to 0.85, Critical above) are fixed cut points on that index, chosen for readability, not calibrated thresholds. Scoring rules published 2026-09-07.
Pathogen drivers
| Pathogen | Loves | Hates |
|---|---|---|
| Botrytis (gray mold) | RH > 60%, temp 60-70°F, still air, leaf wetness | Low RH, strong airflow, dry leaves |
| Powdery mildew | RH 55-90%, moderate temp, still air, leaf wetness | Direct UV, very low RH, strong airflow |
| Spider mites | Temp > 80°F, RH < 40%, low airflow, dry conditions | High RH (mite predators thrive there too) |
| Russet mites | Temp 70-85°F, RH moderate, dense canopy | (cannabis-specific; harder to spot) |
| Pythium (root rot) | Root temp > 75°F, low DO, waterlogged substrate | Cool roots, well-oxygenated water |
| Fusarium | High root temp, high RH, plant stress | Cool roots, healthy plants |
| Septoria leaf spot | Leaf wetness, temp 60-80°F, high RH | Dry leaves, low RH |
| Damping-off (seedling) | High RH, cold soil, sterile substrate, weak airflow | Warm soil, beneficial microbes, airflow |
| Aphids | Spring temps, high N tissue, weak predators | Cold; dry; predator-friendly polyculture |
| Whitefly | Warm + high N tissue + sheltered conditions | Cold; predator-friendly habitats |
Severity reference
- Pressure 0.00-0.30: Low risk. Conditions don't favor this pathogen. Standard monitoring.
- Pressure 0.30-0.60: Moderate. One or two factors are favorable. Inspect; consider light prevention.
- Pressure 0.60-0.85: High. Multiple drivers aligned. Active prevention warranted (airflow, RH adjustment, foliar drench).
- Pressure > 0.85: Critical. Conditions are textbook for this pathogen. Aggressive intervention; environmental adjustment is urgent.
Most common interventions
- Lower RH: fastest path to reducing botrytis, powdery mildew, septoria pressure. Dehumidifier capacity often the limit.
- Increase airflow: moves boundary-layer humidity off leaf surfaces; mechanical disruption of spore landing.
- Eliminate leaf wetness: water early in photoperiod; avoid foliar applications close to dark; ensure good drying time.
- Cool root zone: reservoir chillers for hydroponic; insulate / raise pots in soil-based for outdoor heat events.
- Oxygenate root zone: air pump in DWC; moisture cycling in coco/peat to allow drying back.
- Beneficial inoculation: Trichoderma harzianum out-competes Pythium; Bacillus subtilis suppresses powdery mildew; predatory mites for spider mites.
Free under CC BY 4.0. Cite as "Open Agriculture Technology Pathogen Pressure Forecast (openagriculturetechnology.com)". Pressure indices synthesized from peer-reviewed plant pathology literature.