Since 1992 elm trees have been treated with a biological control product Dutch Trig® to protect them from infection by Ophiostoma novo-ulmi causing Dutch elm disease (DED). The active ingredient of the biocontrol product consists of the fungus Verticillium albo-atrum strain WCS850. A conidiospore suspension of this fungus is injected into the vascular system of elm trees at a height of 1.3 m. This biocontrol product prevents healthy elm trees from fungal infection transmitted by elm bark beetles. Dutch Trig®, however, does not protect already infected trees or trees connected with diseased trees via root grafts. Since 2010, only 0.1 % of the injected elms became infected with DED through beetle transmission and an additional 0.4 % of the treated elms were infected through root contact in the Netherlands. Regression analysis considering all injected elm trees in the Netherlands since 1992 indicated that DED infection through beetle transmission had significantly decreased during the 24 years application of Dutch Trig®. In 2015, approximately 28,300 trees in five countries (Netherlands, USA, Germany, Canada and Sweden) were treated with Dutch Trig® to protect valuable susceptible elm trees, mainly in urban environments.