Using Climatic Data for On Farm IPM Decisions

James Frisby
Plants, Soils and Biometeorology Department,
Utah State University

            Plants, insects and microorganisms are poikilothermic (cold blooded), meaning they develop at a rate dependent on the heat found in the environment. Phenology models use temperature, usually daily maximum and minimum temperatures, to calculate heat units like degree-days (DD). Cumulative DD are used to optimize pest control measures (i.e. first codling moth cover spray at 250DD after biofix). Other useful weather information includes: leaf wetness, precipitation, relative humidity, wind speed and direction in order of relative importance.

            Weather data is available from various sources. One can find the maximum and minimum temperatures, and precipitation levels in newspapers, TV newscasts, and internet sites. Alternatively, one can use temperature data collected with a weather station.

            Once the temperature data has been collected, it must then be converted to DD. Look-up tables can be used to calculate daily DD using the daily maximum and minimum temperatures (see degree day look-up table). Daily values are then summed. Forecasted or normal temperatures  (30 year average) can be used to predict what the cumulative DD will be for the next few days.


            Washington State University has made available a spreadsheet to calculate insect DD using daily maximum and minimum temperatures. The spreadsheet comes with normal temperatures for Yakima, WA. These temperatures should be replaced with normal temperatures calculated for a station near your orchard. Then simply overwrite the normal temperatures with those measured. I like to change the cell color, to keep track of which cells I have changed. To set the biofix, simply type zero on the summed value cell for that day. The spreadsheet can easily be modified according to personal taste.

            Orchards in Utah are found at various elevations and aspects. There are diverse climates and microclimates. Growers can use the DD recommendations given out by the extension service. Yet, even within relatively small distances, there can be large differences in bloom time and insect development. Growers desiring precise IPM control could collect their own temperatures data from various orchard areas and calculate the corresponding DD. After comparing the DD with recommendations provided by the extension service, they would be used to give precise pest control timing.

            Individual weather stations can range from simple to very expensive. The simplest station consists of maximum and minimum thermometers ($35 and up). Battery operated electronic sensors are available for about $20 at department stores. The problem with these stations is that they require daily maintenance. Every day, the maximum and minimum temperature must be recorded, and the equipment reset. This may seem like an unpleasant task, but there are many volunteers and employees that do this very thing every day.

           Inexpensive sensors may also need to be calibrated. Calibrating a thermometer or sensors is simple. Put the thermometer or sensor in ice water. Stir the ice water. The sensor should read 32 °F or 0 °C. If the sensor read something else, the difference should either be added or subtracted from future readings, to get the correct temperature.

            To get reliable temperature data, instruments must be located in a shelter. A shelter protects instruments from direct sunlight and from rain (irrigation). A shelter must also allow good airflow (Figure 1).

            More expensive HOBO or WatchDog data loggers (about $100) can be used to collect temperature data at regular intervals (i.e. every 10 minutes). Using small shelters, these stations can be placed directly in the tree canopy (Figure 2). These stations do not need to be maintained daily. Still, the temperature data does need to be accessed (uploaded) before it can be used. The data can be uploaded directly to a computer (laptop), or to a shuttle ($240), then to a computer. The readings need to be manipulated to filter out the daily maximum and minimum temperatures (BoxCar Pro for HOBO software $100). SpecWareTM (Spectrum Technologies $100+) software can read both WatchDog and some HOBO data loggers, and calculate the corresponding DD data from the raw data.


            There are many “hobby” weather stations made by various companies for about $300 each (Peet Bros. Company, Inc., Columbia Weather Systems, WxSystems, RainWise Inc., Scienfic Sales, Inc., etc.). Most of these stations monitor indoor and outdoor temperature. Depending on the configuration, these stations may also measure relative humidity, precipitation, wind speed and direction. Many of these stations still require the user to record the daily maximum and minimum temperatures manually (some every other day). Some stations can be connected to data loggers (another $300+) to collect the data over time. These data loggers are then connected to a computer intermittently, to save and access the recorded data. Degree-day calculations are either done by hand or with a spreadsheet.

            Grower stations are available for about $1,200 and up (Spectrum Technologies, Inc., Davis Instruments Corp., etc.).  These stations appear to be easy to set up and use. They can be access directly by a computer or through a wire, telephone or radio. Cellular phone options may be available soon. The IPM Project at USU is planning on using some of these systems this growing season. Spectrum Technologies (SpecWareTM) and Davis (GroWeather) have software that calculates the DD directly from the raw data collected by their grower stations. These stations can also be modified with leaf wetness sensors. Leaf wetness and temperature data are required for the apple scab and fire blight phenology models. Relative humidity and wind speed are required to calculate evapotranspiration.

            Professional systems are much more expensive ($5,000+). They have the advantage of being very flexible, but require someone with training and expertise to set up, maintain, and access the data. These systems can be accessed by various methods including: computer, storage module (like a shuttle), telephone, cellular phone, radio, satellite, etc. Data collected from stations maintained by the Utah Climate Center at USU are used by the Extension Service to make IPM recommendations for Kaysville, Spanish Fork, Santaquin, and West Mountain (South Shore Farms, See figure 3). The stations at Santaquin and West Mountain also have leaf wetness sensors.


Last year the Utah Climate Center provided DD, plant growth units, plant chill units, etc. for the Santaquin, West Mountain stations [SARE-WR (98-058) grant]. Due to technical difficulties and the end of grant funding, this was no longer possible. A new program was created that makes these calculations directly on the data logger. The Utah Climate Centers’ orchard stations are now set up to calculate codling moth DD, plant chill units, plant growth units, ‘Red Delicious’ apple floral bud stages, and early codling size. The Extension IPM Project Leader will have direct access to these stations for up to the hour information. Also, interested growers can have their computer set up to monitor nearby stations.

Potential Grower Options:

  1. The best method would be to use a grower station with the appropriate DD and disease software. The expense will limit the number of stations possible. It is wise to compare generated DD values with information provided by the Extension IPM project leader. The Extensions IPM project leader would be interested in temperature, and phenology model information, that growers provide.
  2. HOBO or WatchDog systems are simple to use. The cost is relatively low per station. These could be used alone, or to supplement data from a main grower station. SpecWareTM software can calculate DD from the data uploaded from a WatchDog and some HOBO data loggers (Warning: The current version of SpecWareTM simply skips any missing days). Otherwise, a table or spreadsheet could be used to calculate the DD.
  3. Several growers in an area could contract with the USU UCC to set up a station in their area. This would be most useful to USU, and nearby growers, but probably too expensive for a single grower.
  4. Use a hobby (personal) weather station. It is best to get a station that can be accessed by a computer, or one that retains maximum and minimum temperatures for a few days.
  5. Monitor thermometers or electronic devices daily. Do it at the same time every day.
  6. Adjust the recommendations, given by the extension service, up or down a few days according to how you feel your specific orchard compares with a nearby area.

To get on the IPM pest advisories email list, please contact Dr. Diane Alston at

Listing of commercial products implies no endorsement by the author, the Plants Soils and Biometeorology Department at Utah State University, the Utah Climate Center, or the Utah State Cooperative Extension Service. Criticism of products not listed is neither implied nor intended.