Fate of fungal biocontrol agents and their non-target effects on the native cultivable mycobiota in strawberry agroecosystems.

Fungal biocontrol agents (BCAs) are increasingly used in plant protection, but information about their establishment and fate as well as non-target effects under field conditions is yet limited, hampering the development of efficient and safe field application strategies. In field and semi-field experiments with strawberry, the fate of the fungal BCAs Trichoderma harzianum (strain T22), Clonostachys rosea (strain IK726) and Ulocladium atrum (strain 302), and their non-target effects on the native cultivable strawberry mycobiota on ripe berries was investigated. In two strawberry fields, T. harzianum was sprayed at recommended dosage on labelled flowers and green berries. At the time of application and subsequently on ripe berries about 3-4 weeks after the initial treatment, depending on the de individual experiments, the population density of T. harzianum was quantified. Overall, there was a strong decline in T. harzianum population density from flower and green berry application to ripe berries. In a semi-field experiment where all three BCAs were sprayed on flowers both alone and in combination with the fungicide Teldor® WP no effects were observed on the native cultivable mycobiota on the ripe berries irrespective of the fungicide application. Furthermore, the abundance of T. harzianum and C. rosea declined to the lowest detectable level, whereas U. atrum was undetectable on fruits. The presence of T. harzianum (isolate T22) on ripe berries was confirmed using UP-PCR profiling of recovered strains also revealing presence of native Trichoderma isolates. From a risk assessment perspective these results suggest limited effects on the native cultivable mycobiota after field applications of these BCAs in strawberry field production.