Secondary Infections by conidia 

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ConidiaGraphical Presentation of Conidia Infection Progress in fieldclimate.com

Infections of apple scab by conidia (asexual) depend on the same factors as infections caused by ascospores. The difference is, that conidia are able to be discarged under light and dark conditions and conidial infections take mostly place during summer time.

Depending on air temperature regimes the conidia of Venturia inaequalis need longer or shorter leaf wetness periods for germination and penetration into leaves or fruits of the apple tree. This relationship was first published by MILLS and LAPLANTE (1945). Our calculations are carried out based on the publications of SCHWABE (1980). Where Mills and LAPLANTE (1945) only assumed that conidia need a certain time peridod of leaf wetness; SCHWABE (1980) also included the importance of the temperature in the infection process.   


The Conidia Infection Model calculates the progress of infection depending on leaf wetness and temperature for weak, moderate and severe infections. To split the prediction into "three severity classes" is very traditional for apple scab models. The progress of infection is displayed as a graphic for hourly values. An infection has already taken place as soon as the progress curve for a weak infection reaches 100%. A moderate or severe infection is complete if the progress curves for this severity classes are reaching 100%. Often in practice or realtiy an infection reach 70% or 80% early in the morning and  in combination with the actual weather you will be able to know if this infection will finish or not. Displaying the daily maximum values of the infection progress curve gives an overview over the expected infection dates in the season.  

For the market apple scab free fruits are need for selling. Therefore growers tolerate no apple scab at all in their orchards. The  model can be used in a curative spray program. Curative compounds like cyprodinil or pyrimethanil could be applied in the conidia phase after infection.  

For more Information about the fieldclimate.com apple scab model please look for Pages of Biology and the Model for Infection by ascospores. To learn how to use plant disease models for apple scab control read the page for practical use of the model.



Venturia inaequalis infection, pointing out dates of ascospore and conidia infection (SCHWABE, W. 1980)

Mac Hardy W.E., 1996. Apple scab biology, epidemiology and management. St. Paul, MN: Am. Phytopathol. Soc.: 545.


(c) Dr. Heinrich Denzer, Pessl Instruments GmbH, Weiz, 2007