Hood River Area Extension Agent - Horticulture
Oregon State University
2990 Experiment Station Drive
Hood River, Oregon 97031-9512
The d'Anjou pear scald prediction model estimates the length of time (in
days) after harvest for fruit to develop a physiological disorder known
as superficial scald, which affects the appearance and marketability of
the fruit. The model is based on the amount of time during the 42 days
prior to harvest that the air temperature is less than or equal to 50
degrees Fahrenheit. This is measured as accumulated cold units (ACU)
using hours as the unit of measurement.
There are two linear functions used in the model to predict the number of days in
storage (DIS) prior to scald development:
1. for ACU = 0 to 175: DIS = (0.1229 x ACU) + 74.5 days (+/- 9 days for 95%
2. for ACU>175: DIS =96 (+/- 6 days for 95% confidence interval).
1. The model start date is the harvest date, which is designated by the model user.
2. Based on the chosen start date, the model will first determine the 42 day period
to use for calculating ACU by subtracting 41 (41 because it includes the harvest
3. Then, count all fifteen minute intervals with temperature less than or equal to
50 degrees Fahrenheit during that time period.
4. Divide by 4 to get ACU (hours).
5. Calculate DIS using the equations above.
Model output should include three pieces of information
2) DIS, which is the predicted number of days until scald will appear
3) the corresponding calendar date, which is calculated by adding the DIS to the
IPPC model implementation notes:
1) The model has been developed as part of our national modeling system and is subject
to certain constraints such as a) only weather stations currently ingested into our
national weather database are available. Adcon stations are under conversion now.
Automata stations will depend on future external funding, b) User interface is under
development as a generic, flexible multi-model and multi region tool.
2) A few important features are under development. End-user feedback will be greatly
welcomed in this effort.
3) Model forecasts are a custom Fox Weather/IPPC research program funded by USDA-NRI.
These forecasts are undergoing rapid development. Use with caution.
Pear Scald Model outputs:
1) Graph of DIS +/- 95% confidence interval including 6-day forecasted model results
2) Graphs of weather data such as temperature used to drive the model, needed to verify model inputs
3) Tables of Selected weather data, DIS and ACU by Date and hour (scroll down)
If you have comments or corrections to make, send them to: