Apple scab, caused by the Venturia inaequalis fungus, is, economically speaking, the most damaging disease in apple production worldwide. In order to fight against apple scab, repeated chemical fungicides must be administered in the spring and summer. Over the past two years H39, a potential antagonist based on a specific kind of Cladosporium fungus, has been tested in several European field trails. H39 appeared to be very successful in reducing apple scab on leaves and fruit. The antagonist was able to produce the same results as the conventional chemical fungicide sprays. Currently, a biological pesticide company is investigating the commercial application possibilities of H39. This is an important step because the development of a commercial product can lead to a reduced dependence on chemical pesticides. 

Without fighting against it, apple scab can cause huge losses in yields (70% or more) in areas with moist, cool weather during the spring and summer. The losses are caused by damage from diseased and damaged fruit, and also by leaf loss, which can lead to reduced tree growth and lower fruit yields. 

Using chemical fungicides

In the current fight against apple scab, chemical fungicides are repeatedly used in the orchards. This is used not only in a preventative way, but also as a cure. In recent years, Venturia inaequalis fungus (the fungus that causes apple scab) has developed a resistance to many chemical fungicides in important apple growing areas. In addition, the use of chemical pesticides is being limited by governmental measures, including within the European Union. The increasing demand for fruit with little to no pesticide residues is another reason why alternatives to chemicals are needed.


The antagonist, Cladosporium cladosporioides H39, appears to greatly reduce the spread of the Venturia fungus. Various research institutions have tested the capabilities of this antagonistic isolate over the last two years in orchards with various apple breeds in Hungary, Poland, Germany and the Netherlands. Treatments were carried out with H39 as a calendar spray or in post-infection periods. Trials in the Netherlands (Randwijk) were focused on how the timing of the application effected the situation; so trials were carried out both before and after infection occurred. 

The results of the trials have shown, for the first time, that the use of H39 can reduce apple scab in leaves and fruit in a consistent manner. This was demonstrated in both an organic cultivation environment as well as in the conventional regimented orchards in the spring and summer. The same results achieved with conventional chemical control schemes can also be achieved using H39. Leaf scabs were reduced by 42-98% and fruit scabs were reduced by 41-94%. 

The next step is developing H39 into a commercial biological crop protection agent. One company has already started researching the possible commercial application of the H39 antagonist. 

Source: WageningenUR