Understanding Leaf Wetness

What is leaf wetness and what is it used for?

Leaf wetness refers to the moisture on the surface of a leaf, which can be caused by rain, dew, fog, mist, frost or irrigation.

Leaf wetness can be measured using sensors that detect the presence and duration of moisture on a leaf's surface. This information is useful in disease management to monitor plant health and predict potential disease outbreaks. Additionally, leaf wetness data can be used to:

1. Optimize irrigation and pesticide spray timing
2. Monitor humidity levels and plant health
3. Predict the likelihood of fungal disease development
4. Assess the need for pest and disease control measures
5. Optimize irrigation schedules to prevent excess moisture build-up on leaves
6. Study the effects of environmental conditions on plant growth and development

How do I know what model of leaf wetness sensor I have?

The Yield supports two models of leaf wetness sensor. To determine which sensor you have, use Figure 1 below and match it to your sensor.

To work out which platform your sensor is using, microclimate sensing system (MCSS) soil moisture sensors are displayed with 1 decimal place, while Davis sensors are displayed as whole numbers.

Figure 1: Which sensor do you have?

What it looks like	Name	Supported by
		Davis	MCSS
	METER Phytos 31 also known as Decagon Leaf Wetness Sensor LWS
	Davis 6420 Leaf Wetness Sensor

How do I know if the leaves of my crop are wet?

There is a threshold that you can use for determining when leaves are wet. To determine the exact threshold values for each of your leaf wetness sensors, you will need to compare the values displayed in The Yield mobile app to field observations of how wet the crop’s leaves are.

Both sensors will detect small amounts of water, so sometimes a sensor will measure moisture even if you can’t visibly see it. Below is a table for typical thresholds for both the Davis and MCSS sensors.

Figure 2: Typical thresholds for leaf wetness. Actual values will vary from sensor to sensor and location to location.

If you have multiple leaf wetness sensors you may see varying leaf wetness values across your site, sometimes with a difference of 10%-20%. It is worth noting that, although a leaf wetness sensor might be in a similar location, the foliage around the sensor can look different at each location, which can then affect the readings.

How does the Davis leaf wetness sensor work?

View the Davis Leaf Wetness Sensor page to read more about this.

How does the METER Phytos 31 and the Decagon Leaf Wetness sensor work?

View the Decagon/METER Leaf Wetness Sensor page to read about this.

How does The Yield predict leaf wetness?

The Yield’s microclimate leaf wetness predictions use a combination of different weather sources to tailor the forecast for your leaf wetness sensor. This includes historical leaf wetness measurements, rainfall, humidity and temperature.

Why can’t I see leaf wetness duration?

The Yield apps currently do not display leaf wetness duration.

What impacts the drying time? 

The drying time of the leaves are impacted by factors such as: 

• Temperature 
• Wind 
• Humidity 

How do I use leaf wetness to support my irrigation decisions?

By monitoring leaf wetness, you can adjust your irrigation practices to provide the optimal amount of water for your plants, promoting healthy growth and reducing the risk of water waste or damage to your crops.

Long periods of leaf wetness can lead to disease outbreaks. If you apply overhead irrigation to your crop, it's important to limit the length of time that the leaves are wet whilst still achieving the desired soil moisture level.

Irrigating a few hours after the morning’s dew has evaporated will reduce the risk of some plant diseases by breaking the disease growth cycle.

How does my leaf wetness sensor measure frost events?

Phytos leaf wetness sensors can be used to enhance your understanding of a frost event. To do this, look at leaf wetness in conjunction with air temperature. During a frost event, the sensor readings will look similar to Figure 3.

In 2020, we measured this frost event in Tasmania, Australia. You can see that as the temperature became colder, the dew formed, increasing the leaf wetness value to ~68%. Once the water on the surface of the sensor froze the values suddenly drop to ~5%. This is because frozen water is a weaker conductor than liquid water. Once the temperatures begin to warm again during the late morning, the ice melts, increasing the leaf wetness values before decreasing as the water evaporates.

Figure 3: Using the Phytos 31 leaf wetness sensor we were able to determine that the frost event lasted 6.5 hours even though the air temperature was below 0^oC for 9.5 hours.

Do I need to perform maintenance on the leaf wetness sensors?

Maintenance of your leaf wetness sensor is important – any dust or dirt on the sensor can create false / increased wetness readings, therefore make sure to include cleaning of the leaf wetness sensors onsite in your maintenance cycle.

Can I setup a leaf wetness notifications?

Yes you can! Visit Introduction to Notifications in The Yield app for more information.

Leaf wetness notification examples

An example for harvesting: You may want to ensure that the plants are dry before harvest, therefore set a notification such as: 

• Leaf Wetness is above 5% – ‘DO NOT HARVEST’ 
• Leaf Wetness is below 5% – ‘Safe to harvest’ 

For Disease, identify and input the factors that impact your crop that could lead to disease. 

• An example may be, leaf wetness being over 5% for a number of hours over a day, in combination with temperature. 

I want to learn more, can you share more information on my leaf wetness sensor?

Check out the following articles:

• Davis Leaf Wetness Sensor
• Decagon/METER Leaf Wetness Sensor 

Need Assistance?

For any questions regarding this or assistance with The Yield's apps, please contact Support via the contact details provided in How can I get in touch with The Yield's Support Team.