Abstract: The European red spider mite, Panonychus ulmi, can cause severe damage on manyfruit crops, especially on apple. Outbreaks of mite populations usually occur in summer on warmand humid days. Natural occurring predator populations may not always be able to keep the pestunder control, especially because of the likely occurrence of a lag in time in build-up of prey andpredator populations and due to the use of non-selective chemical pesticides. The efficacy of themicrobial control agent Beauveria bassiana strain ATCC 74040 (Naturalis®) against P. ulmi wastested in open trials on apple. In one of the trials, also observations on the potential side effects ofthe formulated product on natural occurring predator populations (Phytoseiulus spp. andStethorus punctillum) were made. The microbial control agent showed high efficacy againstP. ulmi in all field trials, and did not adversely affect predator populations. Beauveria bassianastrain ATCC 74040 can be considered a valuable tool to be integrated into P. ulmi controlstrategies.