--- title: "Leaf Wetness Sensors & Monitoring | Aethair" description: "Leaf wetness is free water on plant surfaces: dew, rain, fog, or irrigation. How wetness duration drives disease models and how to monitor it." url: https://aethair.io/parameters/leaf_wetness/ --- Measurements · Agriculture # Leaf Wetness Also known as leaf wetness sensor Leaf wetness (disease/irrigation indicator). [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Leaf Wetness Monitoring](https://aethair.io/build/?params=leaf_wetness) At a glance — Agriculture 1 way to measure it - **Thiamis** 1 external instrument What it is ## What is leaf wetness? Leaf wetness is the presence of free water on plant surfaces: dew, rain, fog, or irrigation that has settled on leaves and not yet evaporated. What matters agronomically is how long a leaf stays wet. Leaf wetness is therefore usually reported as a **wetness duration** (the time the canopy stays wet) or as a simple wet-or-dry state, often on a dimensionless scale or percentage, which is why it carries no standard unit. A threshold set on the sensor's signal defines the moment the surface counts as wet. Leaf wetness typically builds overnight as dew forms and clears after sunrise as the canopy dries. Because so many plant diseases depend on surface moisture, the number of hours a canopy stays wet is a key input to the models that predict when crops are at risk. Most fungal and bacterial plant pathogens need free water on the leaf to germinate and infect, and the risk rises with the number of continuous hours the surface stays wet, in combination with temperature. Disease-forecasting models (for blights, mildews, rusts, scab, and many others) use leaf wetness duration and temperature to predict the infection periods when a crop is vulnerable. Growers can then time fungicide sprays to actual risk rather than a fixed calendar. This targets applications where they are needed, cutting both unnecessary spraying and disease losses. For growers and agronomists, leaf wetness is therefore the trigger variable in integrated disease management, converting weather into a spray-or-wait decision. How it is measured ## How Leaf Wetness Is Measured Leaf wetness is measured with a **leaf wetness sensor**, a flat plate carrying an electrical grid whose resistance or dielectric property changes as water condenses on it, so the sensor mimics a leaf and detects when free water is present. As a professional field sensor rather than a built-in reading, it is connected to a Thiamis gateway for continuous logging of wetness state and the accumulation of wetness hours. The wet/dry threshold and, on some sensors, a coating that emulates a real leaf's surface, are set so the sensor wets and dries at the same time as the crop it represents. An instrument on Thiamis 1 A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account. ### Placing leaf wetness sensors A leaf wetness sensor is mounted within the canopy at a representative height and angle, typically inclined like a leaf, so that it collects dew, intercepts rain, and dries at the same rate as the surrounding foliage. Placement matters greatly: a sensor too high, too exposed, or at the wrong angle will wet and dry out of step with the crop and mislead the disease model. It is sited among healthy representative foliage rather than at the very top or bottom of the canopy, and kept clean, since dust and residue change how it holds water. ### Every device and option that measures Leaf Wetness 1 | Device / option | Type | Base platform | Measures | | - | - | - | - | | [Davis](https://aethair.io/sensors/davis-weather-stations/) · Davis Wizard III, Davis Wizard II, Davis Monitor… | Weather Stations | Thiamis | Leaf Wetness [Dew Point](https://aethair.io/parameters/dew_point/) [Heat Index](https://aethair.io/parameters/heat_index/) [Relative Humidity](https://aethair.io/parameters/humidity/) [Leaf Temperature](https://aethair.io/parameters/leaf_temperature/) [Precipitation Intensity](https://aethair.io/parameters/precip_intensity/) [Precipitation](https://aethair.io/parameters/precipitation/) | [Configure Leaf Wetness Monitoring](https://aethair.io/build/?params=leaf_wetness) Where it is monitored ## Solutions That Monitor Leaf Wetness Each one links to the solution page showing what that industry measures it for. ### [Agriculture & Irrigation](https://aethair.io/solutions/agriculture/) Often added Soil moisture, microclimate, and frost warning Related ## More in Agriculture [Soil Temperature](https://aethair.io/parameters/soil_temperature/) [Soil Moisture](https://aethair.io/parameters/soil_moisture/) [Leaf Temperature](https://aethair.io/parameters/leaf_temperature/) Questions ## Leaf Wetness FAQ What unit is leaf wetness measured in? There is no standard physical unit. Leaf wetness is reported as a wet-or-dry state, or as accumulated hours of wetness, and some sensors give a dimensionless index or percentage of a scale. What matters for agronomy is the duration the canopy stays wet, so wetness hours is the value most disease models use. How does a leaf wetness sensor work? It is a plate with an electrical grid whose resistance or dielectric response changes as water condenses on its surface, so it detects the presence of free water much as a leaf would. A set threshold marks the transition to wet, and the logger accumulates how long the surface stays above it. Why is leaf wetness important for plant disease? Because most fungal and bacterial pathogens need free surface water to germinate and infect, and their risk grows with the continuous hours a leaf stays wet at a suitable temperature. Feeding wetness duration and temperature into a forecasting model shows when infection periods occur, so sprays can be timed to real risk. How do I monitor leaf wetness? Pair a Thiamis gateway with a leaf wetness sensor mounted within the canopy at a representative angle for continuous logging of wetness duration. Use the configurator to combine leaf wetness with temperature, humidity, and leaf temperature so that disease-risk models have all the inputs they need.