One relative-humidity reading cannot answer whether a strawberry crop is facing Botrytis or powdery mildew. Start with the host, tissue, suspected pathogen, and observed conditions. Separate free water and leaf-wetness duration from high-RH and powdery-mildew evidence. A dry leaf does not rule out strawberry powdery mildew, and RH does not prove a Botrytis event.
Botrytis: ask where free water persisted
UC IPM’s strawberry guidance links Botrytis fruit rot to the strawberry host, including flowers and fruit. Its discussion describes spores exposed to free water in cool conditions, with wetness duration, drying, and local microclimate affecting interpretation. Treat “wet” as a condition at a particular tissue and time, not a greenhouse-wide conclusion. A sensor or visual check documents an event; it does not establish an infection threshold or diagnose the crop.
For this branch, record crop location, tissue, time window, whether free water was seen, and whether the surface later dried. If a leaf-wetness sensor is used, retain its location and represented period. Leaf-wetness duration observes how long a surface stayed wet; it is not a universal Botrytis setpoint.
Strawberry powdery mildew: dry leaves can still matter
UC IPM’s strawberry page identifies Podosphaera aphanis and describes ideal infection conditions as dry leaf surfaces, high relative humidity, and cool-to-warm air temperatures. It also notes severity in greenhouse and plastic-tunnel production. This differs from a Botrytis observation of free water on flowers or fruit. Do not convert the wording into a universal RH percentage or treat a dry leaf as proof that powdery mildew risk is absent.
When this branch is suspected, record crop location, affected tissue, visible signs, time, RH, temperature, and whether free water was observed. Keep the suspected pathogen explicit until a qualified person reviews the crop. Environmental records organize the question; they cannot replace diagnosis.
Compare the evidence before changing the question
| Branch | Record first | Do not infer |
| Strawberry Botrytis | Flower or fruit location, free water, wetness duration, cool or drying context | A greenhouse-wide RH threshold or infection diagnosis |
| Strawberry powdery mildew | P. aphanis as the strawberry-specific reference, dry surface, RH, temperature, crop context | That wet leaves are required, or that one RH target prevents disease |
The same room can produce different observations at different heights, tissues, or air paths. Keep location and time beside the reading. Compare like observations, and bring the record and symptoms to the agronomy team rather than collapsing both branches into “mold.”
A practical observation handoff
Use a short record with: crop zone; plant or row; tissue; date and time; RH and temperature; visible free water; leaf-wetness method; drying or condensation context; symptoms; and the handoff question. Mark each item as measured, visually observed, or unknown. Bring unresolved crop questions to a qualified agronomy reviewer.
Keep the equipment question separate
These observations can help define a conversation about the operating environment, but they do not prove that a dehumidifier prevented disease or establish a required humidity target. For equipment placement and airflow context, see strawberry greenhouse dehumidification and mold prevention. For the separate leaf-wetness recording topic, see leaf-wetness duration in a greenhouse. The agriculture overview provides the broader application context. Keep disease identification with the agronomy team and equipment evaluation with its own evidence.
