The warning system uses a sensor, placed under the canopy of a tree in the orchard at a height of about 4 ft, to measure and record wetness. One sensor is enough for a typical Iowa orchard. The sensor we have used is the Leaf Wetness/Temperature Logger, made by Spectrum Technologies, Inc., Plainfield, IL. (Phone: 1-800-248-8873. Email: specmeters@aol.com)

This electronic, battery-powered sensor has proved generally reliable in our field trials, is about the size of a pack of cigarettes, and is easy to use. We place the sensor on a metal stake under a tree, angled at about 45o to horizontal and facing north. Mounting slots on the sensor fit loosely on a pair of nails or screws secured to a piece of 2"x4" secured to the stake. The miniature datalogger below the sensor can be programmed to record wetness and temperature measurements every hour. (Click on the picture for an enlarged diagram.)

About once per week, you remove the sensor from its pole and transfer the stored data to a computer. The software provided by Spectrum Technologies organizes the weather data in an easy-to-understand format. This piece of equipment is simple to use and fairly inexpensive; the cost in 2001 was $255 for the sensor and $99 for the Specware software needed to interpret the data. Note that you do need a computer for this system, running Windows 95 or a more advanced operating system, with an available serial port.

Alternatively, you could use weather data from Skybit, Inc. (Boalsburg, PA. Phone: 1-800-454-2266) SkyBit is a commercial service that makes computer-derived estimates of weather conditions based on Geographic Information Systems (GIS) technology. This information is emailed to clients every day, thus sparing growers the need to bother with a sensor to measure the weather. This technology is not yet refined enough to save growers as many sprays as an on-site sensor might (see ISU Horticulture Farm Trials), however it is a good option for those who are not willing to manage an on-site sensor.