INFLUENCE OF FUNGICIDES ON THE INSECT PAT HOGENIC FUNGUS BEAUVERIA-BRONGNIARTII (SACC) PETCH

We tested 17 fungicides to check the hypothesis whether they could int erfere with B. brongniartii applied in orchards to control the larvae of the cockchafer Melolontha melolontha L. (Coleoptera, Scarabaeidae). Incorporated into Sabouraud dextrose agar (SDA) at the recommended co ncentration the fungicides Funginex (Triforin), Recop (Cu-oxychlorid), Rondo (Captan + Pyrifenox), Systhane (Captan + Myclobutanil) and Topa s (Captan + Penconazol) completely inhibited mycelical growth, Rondo e ven at a 10 fold dilution. Germination of conidia did not take place w hen they were produced on SDA incorporated with Baycor (Captan + Biter tanol), Captan, Euparene (Dichlofluanid), Nustar + Delan (Flusilazol Dithianon), Ridomil F (Mancozeb + Metalaxyl) at the recommended rate or Systhane (10 fold diluted). Growth of the fungus on barley kernels (commercial preparation) on soils sprayed with fungicides showed small er differences. They were more marked on native soil than on sterile o ne. On both soils, Baycor and Rondo reduced fungal growth more than th e other fungicides. The fungal material from these soil tests was used in bioassays where they caused mortalities between 70 and 100 %. Bayc or, Captan, Nustar + Delan, Rondo and Topas induced the lowest mortali ties. These side effects on 'semi-field'' tests are considered as insi gnificant. In orchards the situation for the fungus is much more favou rable, because it is applied at a soil depth of some centimeters and d irect contact with the fungicides is excluded. It is therefore conclud ed that the tested fungicides have no significant side effects on B. b rongniartii under practical conditions. Exceptions might, however, are indicated where slowly degradable triazoles are applied repeatedly or in soils accumulated with copper.