There are several options for the targeted control of sugar beet weevils, including foliar application of the endophytic insect-pathogenic fungus Metarhizium spp. Upon contact with the weevil, spores adhere to the insect epidermis, germinate and penetrate the cuticle, which results in a lethal infection. However, spores can also persist on the leaves or germinate and develop an endophytic lifestyle in the sugar beet plant, which may also result in fungal infection when such leaves are consumed by the insect. The goal of the present study was to investigate whether our production strain M. brunneum Ma43 is able to successfully establish itself in the plants and persist endophytically after leaf and/or soil application. First results showed that the production strain can grow within the plant tissue. Applying the fungus had a positive effect on the biomass, especially the spray application lead to higher fresh weight (increase of 10 g in mean value) and larger leaves (2 cm larger). To what extent the fungus is able to persist in the plant is under current investigation.