NAME:                   Erysiphe necator secondary infection

VERSION:                1-004

DATE:                   2016/03/03

AUTHOR:                 dr. Hlaszny, Edit

SHORT DESCRIPTION:      Powdery mildew of grapevine is the most enduring and 
                        persistent disease problem in Vitis vinifera vineyards.
                        The impact powdery mildew infection has on a vineyard 
                        often depends on the timing of the first infection. 
                        Once primary infection has occurred the disease switches
                        to its secondary phase. Secondary colonies (white mildew
                        patches) form in 7 to 10 days, although the disease is 
                        not noticeable early in the season. 

                        The white patches of powdery mildew produce millions of 
                        spores (conidia) which are spread by wind to cause more 
                        infections. Free moisture is not needed for secondary 
                        infection; temperature is the most important environmen-
                        tal factor. The disease spreads quickly in early summer 
                        when temperatures are moderate.
                                                
KEYWORDS:               Erysiphe necator; 
                        fungus; 
                        grapevine powdery mildew; 
                        secondary infection

INPUT:                  BBCH
                        current_air_temperature 
                        current_date
                        current_leaf_wetness 
                        current_wind_speed 
                        input_from_field_book_spraying_has_been_done
                        spraying_after_primary_infection_is_happened

OUTPUT:                 spraying_should_be_done
                                                
PROCESSING STEPS:

    START_OF_REPETITION_AT_END_OF_PROTECTION
    
        //
        //  evaluating critical phenological growth stage (BBCH)
        //  (from third leafs unfolded stage to beginning of ripening)
        //
        IF (BBCH  < 13 OR  BBCH > 81)                                       
        THEN
            //  the critical phenological growth stage is over
            BREAK_FROM_REPETITION;
        END-IF
         
        //  if spraying after primary infection is happened, this
        //  fact defines implicitly the end of protection made by the 
        //  previous spraying
        
        LET  START_DATE  be  end of protection made by the previous spraying ;

        //  RISK_INDEX has to be initialized.
        //  Remark: RISK_INDEX should be reset after the spraying
        
            LET  RISK_INDEX  be zero.
               
        START_OF_REPETITION_ON_DAILY BASIS
       
            //  the 1st date when the conidial infection can appear is 
            //  end of protection made by the previous spraying + 5 days.
            //  This is the reason why we have started with 3 days (3 < 5).
            //  So the 1st day is the end of protection made by the previous 
            //  spraying, the 2nd one is the next day and so on...
               
            // (1) computing risk idx from three consecutive days' 
            //     temperature interval
            
                   LET  FIRST_COMPUTING_DATE  be  START_DATE  + 3 days ;
                   
                   Three consecutive days with at less 6 hours (within each day) 
                   between 21-30 C  elevates the RISK_INDEX with 10.
                   
                   Three consecutive days with at least 6 hours (within each day) 
                   between 21-30 C  elevates the RISK_INDEX with 20.
                   
                   Three consecutive days with at least 6 hours (within each day) 
                   between 21-30 C  AND at least 1/4 hour (within each day) 
                   above 35 C decreases the RISK_INDEX with 10. 
              
            // (2) indexing the UCDavis-table (see Appendix) with the art of 
                   chemical and with risk index. Result is the SPRAYING INTERVAL
            
            // (3) START_DATE is the end of protection of the previous spraying
            
            // (4) evaluating whether spraying is needed or even not
            
               IF (START_DATE + SPRAYING_INTERVAL >= current date)
               THEN
                   //
                   // 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%                 
                      )
                   THEN
                       spraying_should_be_done ;
                   ELSE
                       //  spraying cannot be done,- it will be made in the 
                       //  next suitable days, probably. The exact day of 
                       //  spraying can be taken from the field-book
                   END-IF
               END-IF
            
               //  the effective date of the spraying should be taken 
               //  from the field book
            
               IF (input_from_field_book_spraying_has_been_done)
               THEN
                   LET  RISK_INDEX  be zero
                   
                   BREAK_FROM_REPETITION;
               END-IF
               
        END_OF_REPETITION_ON_DAILY_BASIS  
        
    END_OF_REPETITION_AT_END_OF_PROTECTION    
   
Appendix:               UCDavis table for Powdery Mildew 
                     
                        Risk Index      Spray Material  Spray Interval 
                        0 to 30         sulfur dust        14 days*
                                        micronized sulfur  18 days*
                                        DMI fungicides*    21 days*
                                
                        40 to 50        sulfur dust        10 days
                                        micronized sulfur  14 days
                                        DMI fungicides     17 days
                                
                        60 to 100       sulfur dust         7 days
                                        micronized sulfur  10 days
                                        DMI fungicides**   14 days
                                
                         *the label maximum should be taken
                        **Demethylation inhibitors such as 
                          Bayleton, Rally, Rubigan.

REMARKS:                n/a

KNOWN PROBLEMS:         The following factors were not taken into consideration:
                        (1) heavy_powdery_mildew_infection_was_previous_year,
                        (2) mild_winter_weather,
                        (3) variety_susceptibility_to_powdery_mildew.


REFERENCES:             
    (1) http://www.agf.gov.bc.ca/cropprot/grapeipm/mildew.htm
    (2) http://www.apsnet.org/publications/apsnetfeatures/pages/UCDavisRisk.aspx
              
                                        oOo
