Commercially grown apples have to be free of scab. Scabbed apples will only be sold for processing. Therefore it is the aim of all plant protection activities in conventional as well as in organic growing to have scab free fruits. Models, which show the apple scab ascospore discharge and ascospore /conidia infection are very important tools to reach this goal.
Two basic types of fungicides against apple scab are used in conventional growing systems: a) Preventative products like Captan, Mancozeb, Dithianone and Strobilurins or b) curative products like Cyprodinil (Chorus) or Pyrimethanil (Scala) or for application in the later warmer periods of the season the DMI fungicides. Actually most of the growers follow a preventative strategy. Nevertheless, a practical preventative strategy is not able to protect apple trees completely because the apple tree grows and develop blossoms, fruits and leaves. Therefore the preventative spray only protects for a period of 4 to 7 days in dependence of the actual growth of the tree. Such narrow spray intervals are not manageable, therefore growers will integrate their experience on the local climate, weather forecast and apple scab models in their spray management. They will schedule the preventative sprays on base of their experience and weather forecast. The apple scab infection models will show them the exact date of infection (weak, moderate and severe) as well as the ascospore/conidia discharge model and with their experience they are able to estimate the importance of an infection. This gives the possibility to act with a curative product if an apple scab infection was too long after the last preventative spray.
In organic apple production lime sulfur pointed out to be the most effective control agent against scab. The optimal control can be achieved if it is sprayed short before infection or into the beginning of infection. This has to be planned on the base of the weather forecast. Sometime we will miss this optimum period and we have to spray into the wet leaves of an nearly complete scab infection. This will still give a good efficacy. The apple scab models are helping to decide if an emergence spray into a nearly complete infection is needed.