NAME:                   Venturia inaequalis (COOKE) WINT.

VERSION:                1-002

DATE:                   2016/02/26

AUTHOR:                 dr. Hlaszny Edit

SHORT DESCRIPTION:      Apple scab, caused by the fungus Venturia inaequalis, is
                        one of the most significant disease of apple. It causes 
                        serious damages in wet vintage. The susceptibility of 
                        variaties is different. Dark brown spots with feathery 
                        margins appear 7 to 21 days following infection by the 
                        pathogenic fungus Venturia inaequalis. 
                        
                        These scabs can help spread the infection, eventually 
                        defoliating the entire tree along with other trees 
                        nearby. Infected apples develop corky lesions which make
                        them unmarketable. Apple scab overwinters in infected 
                        leaves on the orchard floor. Spores (ascospores) are 
                        produced in these dead leaves just about the time that 
                        new growth appears in the spring (green tip stage). They
                        are then discharged during rainy periods, and can be 
                        carried long distances in air currents. 
                        
                        Ascospores land on new leaves, blossoms and fruit, and 
                        if the leaves or fruit are wet long enough for the 
                        spores to germinate, primary infection of fruit and 
                        foliage occurs.
                        
                        The primary scab season lasts until all the ascospores 
                        from last year's leaves have been released. This varies
                        from year to year but typically ends in late June.

                                                
KEYWORDS:               apple scab, fungus, Venturia inaequalis

INPUT:                  avg_daily_air_humidity
                        avg_daily_air_temperature
                        current_air_temperature 
                        current_date
                        current_leaf_wetness    
                        current_wind_speed      
                        daily rain precipitation 
                        no_protection_done
                                                    
OUTPUT:                 spraying_should_be_done

PROCESSING STEPS:       
//
//  evaluating critical phenological growth stage (BBCH)
//
IF (BBCH >= 09  to middle of June
   )
THEN
    LET critical_phenological_growth_stage      IS TRUE
ELSE
    LET critical_phenological_growth_stage      IS FALSE
END-IF

// is the weather suitable for spraying
//
IF ( current_air_temperature >= 5 Celsius       AND
     current_air_temperature < 25 Celsius       AND
     current_wind_speed      < 6m/sec           AND
     current_leaf_wetness    < 46%              AND
     critical_phenological_growth_stage         IS TRUE
   )
THEN
    LET weather_is_suitable_for_spraying        TRUE
ELSE
    LET weather_is_suitable_for_spraying        FALSE
END-IF  

//  
//  Mills-condition ("wet period") 
//      in the last 5 days back to the current date min. 1 row from the Mills-
//      table should semi-continuously be fulfilled, with max. 4h interruption.
//
//      The infection period is considered to start when rain begins.
  
//  The "wet-periods" can be merged.
//  
//  The following Mills-table defines the valid combinations of incidence 
//  of the ascosporal infection 
//
//                          
//  avg daily    ---- wetting period in hours ------  Incubation period
//  air temp [C] light inf  moderate inf   heavy inf  [days]  
//
    25.6         13         17             26         ...
    25.0         11         14             21         ...
    24.4         9.5        12             19         ...
    17.2-23.9    9          12             18           9
    16.7         9          12             19          10
    16.1         9          13             20          10
    15.6         9.5        13             20          11
    15.0         10         13             21          12
    14.4         10         14             21          12
    13.9         10         14             22          13
    13.3         11         15             22          13
    12.8         11         16             24          14
    12.2         11.5       16             24          14
    11.7         12         17             25          15
    11.1         12         18             26          15
    10.6         13         18             27          16
    10.0         14         19             29          16
     9.4         14.5       20             30          17
     8.9         15         20             30          17
     8.3         17         23             35          17
     7.8         19         25             38          17
     7.2         20         27             41          17
     6.6         22         30             45          17
     6.1         25         34             51          17
     5.5         30         40             60          17
                                                           
// is the weather suitable for spraying
//
IF ( current_air_temperature >= 5 Celsius       AND
     current_air_temperature < 25 Celsius       AND
     current_wind_speed      < 6m/sec           AND
     current_leaf_wetness    < 46%              AND
     critical_phenological_growth_stage         IS TRUE
   )
THEN
    LET weather_is_suitable_for_spraying        TRUE
ELSE
    LET weather_is_suitable_for_spraying        FALSE
END-IF  


// AAFC/IRDA Model: 
//
//  (1) Start of rainfall event
//  Date for starting calculations = 1st March
//  Risk indices:
        0 to 1 = no infection can occur
        1 to 2 = minimum threshold: infection can occur only when 
                 there is an extremely high level of inoculum or 
                 when conidia are present
        (secondary infections)
        2 to 3 = light threshold: corresponds to a light infection 
                 according to the Mills table
        3 to 4 = moderate threshold
        4 and over = severe threshold
        
THEN
    spraying_should_be_done ; 
END-IF     

REMARKS:                -        

REFERENCES:     (1) http://www.agf.gov.bc.ca/cropprot/tfipm/applescb.htm
                (2) Crop Guide - CIPRA
                (3) http://enviroweather.msu.edu/aboutThisModel.php?mod=f_as
                (4) http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/AppleScab.aspx
                