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Technical Documentation for a National Plant Disease Risk Model System
Len Coop, OSU IPPC


This system accesses hourly and sub-hourly data from numerous real-time and 
archival weather stations (>16,000 stations, 2013) to compute a variety of plant
disease risk and horticultural models. Currently the following models are available:

1. Apple Scab infection risk - developed as a degree-hour version of the Stensvand modification 
of the standard Mills table for apple scab infection risk, caused by the fungus Venturia inaequalis.
2. Pear Scab infection risk - developed by Spotts and Cervantes (1991), converted for degree-hour 
calculations by Coop and Spotts (2002). This is a fungal disease caused by Venturia pirina. 
3. Gubler Thomas Powdery Mildew - well known index model for powdery mildew of many crops 
including grapes (caused by the fungus Erysiphe necator).
4. Hop Powdery Mildew - developed by Mahaffee and Gent for Pacific Northwest Hop fields, 
modified from G-T powdery mildew model. Caused by the fungus Podosphaera macularis.
5. Cherry Powdery Mildew - developed by G. Grove for Washington Sweet Cherries. Caused by 
the fungus Podosphaera clandestina. 
6. Pearson-Gadoury Powdery Mildew - Grape PM primary infection alternative to Cleisto. PM model 
7. Cleistothecial Powdery Mildew - similar to apple scab, used for initial infection in grape by ascospores,
also known as cleistothcia.
8. Strawberry Powdery Mildew - similar to GT PM with thresholds determined by Miller et al. 2003.
Caused by Sphaerotheca macularis f. sp..
9. Anjou Pear Scald - developed to estimate safe storage time based on temperatures prior to harvest.
10. Fire Blight 2000 - Cougarblight model for disease of pome fruits caused by Erwinia amylovora.
11. Fire Blight 2010 - Cougarblight model revised 2010 by Tim Smith, WSU.
12. Fox-Broome Botrytis infection risk - Used regularly for grape bunch mold and 
for Botrytis cinerea  in other fruit crops.
13. Boxwood Blight infection risk - New/preliminary model to estimate first infections and degree of 
infection of susceptible and highly susceptible varieties of boxwood due to Cylindrocladium pseudonaviculatum.
14. Tomato Potato Late Blight - Adapted from Smith version. A fungus caused by 
Phytophthora infestans in tomato and potato.
15. TomCast Disease Severity Values (DSV) - Used to estimate units of disease development
for black mold caused by Alternaria solani on tomato, and by other pathogens in carrot, celery, and 
tomato.
16. Custom Degree-Hour Accumulation Model - A tool for plant disease epidemiologists to 
diagnose new and invasive plant diseases, and to develop new models.
17. Chilling Hours models - Chilling requirements (hours or units) are typically computed 
to estimate when fruit trees complete dormancy. 


Use these models with caution. Please see our Disclaimer.



   ########
   # Apple Scab model- inverted Mills Table: degree-hours - infection risk only
   #  hourly version: expecting good hourly data
   ########
   This disease is documented in the PNW Plant Disease Management Handbook.
   This model was developed as an inverted Mills Table by Len Coop, documented at OSU IPPC.
   See also http://www.ipm.ucdavis.edu/DISEASE/DATABASE/pearscab.html for more model documentation. 


   Here is the algorithm used:
   if ( $lfwetness < 1 ) {
                $Anomoistcount++;
                $ADH = 0;
                if ( $Anomoistcount > 8.8 ) { $AcumDH = 0 }
   }
   else {
      $Anomoistcount = 0;
      if ( $temp < 32 ) { $ADH = 0 }
      else {
        if ( $temp > 66 ) { $ADH = 66 - 30 }
        else { $ADH = $temp - 30 }
        $AcumDH += $ADH;
      }
   }
   if ( $AcumDH < 175 )           { $Alabel = $gre . "no app_scab" . $stp }
   if ( $AcumDH >= 175 )          { $Alabel = $yel . "scab near  " . $stp }
   if ( $AcumDH > 204 )           { $Alabel = $red . "APPLE SCAB!" . $stp }
   if ( $AcumDH > 275 )           { $Alabel = $red . "SCAB cycle!" . $stp }
   ########



   ########
   # Pear Scab model- Bob Spotts Pear Scab degree-hours - infection risk only
   #  hourly version: expecting good hourly data
   ########
   This disease is documented in the PNW Plant Disease Management Handbook.
   This model was developed by Bob Spotts with additional ideas by Len Coop, documented at OSU IPPC.
   See also http://www.ipm.ucdavis.edu/DISEASE/DATABASE/pearscab.html for more model documentation. 


   Here is the algorithm used:

   if ( $lfwetness < 1 ) {
                $Pnomoistcount++;
                $PDH = 0;
                if ( $Pnomoistcount > 11.8 ) { $PcumDH = 0 }
   }
   else {
      $Pnomoistcount = 0;
      if ( $temp < 32 ) { $PDH = 0 }
      else {
        if ( $temp > 66 ) { $PDH = 66 - 32 }
        else { $PDH = $temp - 32 }
        $PcumDH += $PDH;
      }
   }
   if ( $PcumDH < 250 )           { $Plabel = $gre . "no pearscab" . $stp }
   if ( $PcumDH >= 250 )          { $Plabel = $yel . "scab near  " . $stp }
   if ( $PcumDH > 320 )           { $Plabel = $red . "PEAR SCAB! " . $stp }
   if ( $PcumDH > 350 )           { $Plabel = $red . "SCAB cycle!" . $stp }
   ########



   ########
   # GTPM model-Gubler Thomas Powdery Mildew Index Model- conidial stage only
   #  hourly version: expecting good hourly data
   ########
   This powdery mildew in grape is documented at various websites, including the 
   PNW Plant Management Handbook. 
   See http://www.ipm.ucdavis.edu/DISEASE/DATABASE/grapepowderymildew.html For more details.
   This model is documented at APSnet Online.



   ########
   # HOP PM model- Mahaffee Thomas Powdery Mildew Model- conidial stage only
   #  hourly version: expecting good hourly data
   ########
   This disease is documented in the PNW Plant Disease Management Handbook.
   The basic Hop PM model is documented at U. of Idaho Dept. PSES, and details are documented at Mahaffee, W. F., Thomas, C. S.
, Turechek, W. W., Ocamb, C. M., Nelson, M. E., Fox, A. Gubler, W. D. 2003. Responding to an introduced pathogen: Podosphaera 
macularis (hop powdery mildew) in the Pacific Northwest. Online. Plant Health Progress doi:10.1094/PHP-2003-1113-07-RV.


   ########
   # Cherry PM model- WSU/G. Grove Powdery Mildew Model- conidial stage only
   #  hourly version: expecting good hourly data
   ########
   This disease is documented in the PNW Plant Disease Management Handbook and http://fruit.wsu.edu/cpm.html.
   The basic Cherry PM model has not been fully documented and at this time is considered to be experimental. Use at your own risk. 



   ########
   # Pearson-Gadoury (1987) Powdery Mildew Model
   #  depends upon good hourly data
   ########
   This model is very simple: ascospores are released from overwintered cleistothecia (or chasmothecia) on days when the 
	average daily temperature exceeds 10 degrees C (50 degrees F.) AND daily rainfall (or other form of precipitation) exceeds 
	0.1 inches (2.5 mm). The model is used during bud break and early shoot growth. The model was developed in New York State and
	has been adopted for use in Western Oregon. References include this OSU Extension Paper by Patty Skinkis, and this Cornell Extension Paper by Gadoury et al..


   ########
   # Cleistothecial Powdery Mildew Index Model
   #  hourly version: expecting good hourly data
   ########
	This model is for the primary inoculation of grape by powdery mildew ascospores released from cleistothecia and is a version
	of the model also known as the "2/3 Mills table" model, and is often used in conjunction with the GT PM model, expecially in California.
   This disease is documented for grape in the PNW Plant Disease Control Guide. UC Davis documentation includes this page.


   ########
   # Strawberry Powdery Mildew Index Model
   #  hourly version: expecting good hourly data
   ########
   This disease is documented in the PNW Plant Disease Control Guide.
   This model is documented by:
	
	Miller, T. C., Gubler, W. D., Geng, S., and Rizzo, D. M. 2003. Effects
	of temperature and water vapor pressure on conidial germination and lesion 
	expansion of Sphaerotheca macularis f. sp. fragariae. 
	Plant Dis. 87:484-492.
	
	and available at APSnet Online.


   ########
   # Pear Scald - Anjou Pear Model
   #  hourly version: expecting good hourly data
   ########
   This disease is documented in the PNW Plant Disease Control Guide.
   This model was developed by Jinhe Bai at OSU, and is documented at OSU IPPC.


   ########
   # Fire Blight - Cougar blight 2000 Model
   #  uses daily max and min from hourly temperatures (therefore expecting good hourly data)
   ########
   This disease is documented in the PNW Plant Disease Control Guide.
   This model was developed by Tim Smith at WSU, and is documented at WSU Extension. Note that this version reads 
   hourly-data files and extracts the daily max and min values, and so may differ in output somewhat from 
   the version in the degree-day models database. This version may be sensitive to bad or missing hourly 
   temperature data. Please compare output with the older/standard degree-day version that currently has 
   more comprehensive missing data estimation than this version.


   ########
   # Fire Blight - Cougar blight Model (version 2010 EZ)
   #  NEW version: uses daily Max temperatures derived from hourly data (therefore expecting good hourly data)
   ########
   This disease is documented in the PNW Plant Disease Control Guide.
   See Tim Smith's website for documentation: WSU Extension and Users Guide V2.0.



   ########
   # Broome Botrytis Model
   #  hourly version: expecting good hourly data
   ########
   This disease is documented for grapes in the PNW Plant Disease Control Guide.
   See http://www.ipm.ucdavis.edu/DISEASE/DATABASE/grapebotrytis.html for model 
	documentation (see model 1 of 2).



   ########
   # Boxwood Blight Infection Risk Model
   #  hourly version: expecting good hourly data
   ########
   This disease is supported at this website: NCSU Ornamentals - Boxwood Blight Information.
   See model summary document (pdf) and technical model development spreadsheet (pdf).
   Model Assumptions: Currently (Summer 2013) this model may be overly conservative in that it will predict
	infection based on temperature and leaf wetness alone. Recent data suggest, however that precipitation 
	is required for spore release and dispersal in order to initiate the infection process. Therefore,
	the infection risk index may only be relevant if: 1) regular precipitation occurred during the first part 
	of any leaf wetness event, or 2) irrigation of some form was applied during this same time.


   ########
   # Tomato Potato Late Blight Model
   #  hourly version: expecting good hourly data
   ########
   Model adapted from Smith and Winstel for Potato-Tomato Late Blight.
   Calculated from 6 am to 5:45 am each day.

   If 10 consecutive hours of (leafwetness > 3 OR relative humidity > 90 % ) AND temperature > 10 C,
   then print "infectious spore production"

   If "infectious spore production" event is at least 24 hours old and no more than ten days old and 
   during that time a "Infection possible" event is activated if there are two consecutive days with 
   a maximum temperature between 23 and 30 C. The "Infections possible" is active for three days. 
   Lesions are likely to be visible after that.

   Otherwise "low" is the late bight risk.

   This disease is documented for tomato in the PNW Plant Disease Control Guide.
   This disease is documented for potato in the PNW Plant Disease Control Guide.
   See http://www.ipm.ucdavis.edu/DISEASE/DATABASE/potatolateblight.html 
   See Model 4 for Winstel version
   See Model 14 for Smith version



   ########
   # TomCast Disease Severity Values (DSV)
   #  hourly version: expecting good hourly data
   ########
	This is a widely-used model for diseases including Alternaria solani (black mold) on tomato,  
	http://www.ipm.ucdavis.edu/DISEASE/DATABASE/tomatoblackmold.html (Calif.), 
	early blight, Septoria leaf spot, and Anthracnose on tomato (Midwest), 
	Alternaria leaf blight on carrot, http://www.ipm.ucdavis.edu/DISEASE/DATABASE/carrotblight.html (Calif.), and 
	Septoria apiicola on celery, http://www.ipm.ucdavis.edu/DISEASE/DATABASE/celeryblight.html (Calif.). 
	Disease Severity Values available at: http://www.ipm.ucdavis.edu/DISEASE/DATABASE/dsvtable.html


   ########
   # Custom Degree-Hour Accumulation Model
   #  hourly version: expecting good hourly data
   ########
   This tool can be configured to accumulate degree-hours above a lower threshold 
	and below an upper threshold, as specified by the user. The option of whether 
	these accumulations depend upon leaf wetness is also available. With leaf wetness 
	required, the model can emulate other models such as apple scab, pear scab, 
	cleistothecial powdery mildew, and TomCast DSV. Without the leaf wetness 
	requirement, this tool can be used for such purposes as chilling requirements 
	and general degree-hour accumulations.  Use trial and error to configure new 
	model parameters for diseases for which you have field data but no published 
	model. This allows this website to be used for invasive species when models 
	have been hypothesized but not yet researched or validated.



   ########
   # Chilling Hours models used in Horticulture to predict completion of dormancy
   #  hourly version: expecting good hourly data
   ########
   This calculator allows both the use of a simple count of hours between two temperature thresholds, such 
   as above 32F and below 45F, and the more complex Utah model (Richardson, Seeley, Walker 1977). Insufficient 
   chill hours can result in delayed foliation, and reduced fruit set and quality. See Victoria BC or 
   UC Extension for more complete introductions to chill units and formulas for simple and Utah types of chill units. 


Last updated 09/03/10
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