Forecast model fruitweb scab

The fruitweb scab forecasting model was developed to provide fruit growers with decision support for scab management in apple cultivation. The model simulates the biological processes of ascospore ripening, ascospore ejection, and the interaction of the scab fungus with the leaf. The different processes are graphically displayed and provide information about the course of infection and the severity of a scab infection.

Individual scab management

It is decisive for scab management in fruit growing operations that there is a sufficient fungicide coating in the germination window of the scab spores. The more severe the infection, the better the coating must be to prevent scab infestation.
The users of the fruitweb scab model can recognize the potential of mature ascospores in the model and use this as a decision support in case of announced precipitation. The inclusion of a local weather forecast also indicates which course of infection can be expected when the precipitation events occur. As fruitweb continuously shows the course of the infection, contact fungicides can be applied with increased safety in the infection window, thus weakening or preventing infections in their course. The exact determination of the start of the infection makes it easier to plan and schedule the application of curatively effective fungicides.

Video Tutorial: Introduction to the fruitweb scab model

Schorfvideo Thumb

Two models in one

The fruitweb scab model basically contains two models:

  1. fruitweb Asco: this scab model is a quantitative model. It is calculated how many ascospores are ejected during a rainfall event and how many of them lead to infection
  2. fruitweb Mills: based on an ascosporus emission, the infection index is calculated according to mills. The amount of spores ejected is not taken into account

In the standard setting fruitweb Asco always appears first. Click on the button „To fruitweb Mills“ to go to the Mills model.

Explanation of the graphic for the fruitweb Asco model

fruitweb Asco Schorfmodell

1 Leaf wetness periods
In the lower part of the graphical display, you will find light blue bars directly above the time axis. These indicate leaf wetness periods on the basis of weather data.

2 Periods of rainfall
The dark blue bars indicate the rainy periods.

3 Rainfall
The actually incurred rainfall is displayed as small blue bars. Each bar represents the amount of rain in 30 minutes.

4 Spraying

5 Cumulative rainfall since the last spraying

6 Ascospore potential
The amount of as yet immature ascospores is indicated by the light green area. 100% of ascospores are immature at the beginning of the season. As spores mature and become released in the course of spring, the amount of immature spores decreases. In addition, immature spores on fallen leaves may be lost by substrate decomposition.

7 Mature ascospores
Mature ascospores are indicated by the dark green colour directly above the light green area. Mature ascospores are ready for discharge during the next rain. A large amount of mature spores indicates that a serious scab infection is likely to occur during the next rainy period.

8 Mills infection curve
The grey curves indicates the Mills infection curves in a range of 0 to 100 % for the first discharged spores of each ascospore release event. This shows whether the ejected ascospores have led to an infection or not.

9 Discharged ascospores
Discharged ascospores are displayed by yellow bars. Ascospores alighting on apple leaves will begin to germinate. During germination, spores are highly sensitive to contact fungicides. Fungicide treatments during this period are therefore very effective.

10 Amount of living spores on the leaf
The white area represents the amount of living ascospores on the leaf. There are two developements possible. The area increases, because of new ascospore discharges. The area decreases, because the ascopores die or an infection occurs. Therefor the white area represents the amount of ascospore that can be reached by a contact fungicide.

11 Infecting spores
The red line indicates an increasing number of spores at advanced stages of germination, ready to penetrate the leaf surface. These spores do not require free water (leaf wetness) for subsequent stages of their life-cycle. Further, they are no longer sensitive to contact fungicides. Curative fungicides are required in order to fight scab infections at this late stage.

Explanation of the fruitweb Mills model

fruitweb Mills Schorfmodell

1 Released ascospores
Discharged ascospores are displayed by yellow bars. At the fruitweb Mills model they have the function to set the beginn of the scab period. The number of released Ascospores have no impact on the calculation of the Mills infection curve. This is the task of the fruitweb Asco model.

2 Mills infection curve (0 to 100 %)
The Mills infection curve is displayed in grey in the range of 0 to 100 %. The curves start with 0 % when the first ascospores are discharged. The infection curve shows whether the ascospores have led to an infection or not. For the calculation of the infection curve we use the revised Mills table.

3 Mills infection curve (100 – 220 %)
Above 100 % the Mills infection curve is displayed in red. The height of the infection curve indicates the severity of a scab infection. ATTENTION: this curve does´t consider the number of ascospores. This is the task of the fruitweb Asco model.

4 Identification of infection severity according to Mills
The dashed lines indicate the severity of the infection according to Mills. The division is made in light, medium and heavy.

5 Switching to fruitweb Asco model
With the button „Show fruitweb Asco“ you can switch to the Asco model.


The fruitweb Asco Model has to be initialized by a starting point. This is done by the so-called Biofix.

The Biofix describes the date on which the first ascospores can be ejected. This can be done by examining the pseudothecia under the microscope or by the shake out method of Kollar.

Alternatively, the Biofix can be determined by the stage of green tip of an early apple variety (Boskoop, Jonagold, Delbarestivalle, Holsteiner Cox).

For the major fruit growing regions the Biofix will be set by us. If you are outside these areas, then please send us the Biofix for your location. By setting „Biofix individual setting“ you can overwrite the general Biofix setting.


In the fruitweb Asco scabmodel it is possible to show the fungizide sprayings in the graph. Below the graph you can find the tab „Edit Sprayings“. There you can set up various field to establish spraying programs. Beside date, time and fungizide you have to set the duration of the fungizide cover.

Spritzungen anzeigen lassen

1 Choose field
If you have set up several fields you can choose the field you want to display here.

2 Set the presentation of the cover decrease
There are three possible ways to show the decrease of the fungizide cover.

  • Efficiency 100%: the fungizide cover has an efficiency of 100% during the whole length of coverage. This is not a realistic way of presentation but it makes it easier to estimate the amount of ascospores that come to an infection after the fungizide cover ends.
  • Efficiency 75%: in this presentation we start with an efficiency of 98% [4]. The efficiency decreases during the length of coverage linear to 75% [5]. Washing away by rain and the increase of leaf area stay unconsidered.
  • Calculated Degragation: in this presentation we do not consider the set length of coverage. Instead we calculate the degragation of the fungizide efficiency by considering the rain and the increase of leaf area. The end of the fungizide cover is reached when the calculated efficiency is 75%. This value can be changed in the scab settings (Edit scab settings > Sprayings).
    PLEASE NOTICE: This function is not yet validated. The results should therefore be treated with caution

3 Show / hide sprayings
With this button you can show / hide the sprayings in the graph.

Weather data – the basis for fruitweb scab model

The basis for the simulation of apple scab is the recording and transmitting of weather data through a weather station. The fruitweb GmbH offers various weather station types to suit different situations and needs. Some of the stations may also be used for a reliable frost warning. An overview about the different weather stations you can find here.