Effects of Carbendazim on the Nematophagous Fungus Hirsutella rhossiliensis and the Ring Nematode.

The nematophagous fungus Hirsutella rhossiliensis Minter and Brady parasitizes CriconemeUa xenoplax (Raski) Luc & Raski in many California stone fruit orchards (5). We assume that the nematode population density would be higher if the fungus were absent, but the suppressive effect of the fungus has not been quantified in the field. Biocides have been used to inhibit antagonists of pests and thus to quantify the suppression caused by the antagonists (2,6). The objective of this study was to determine the suitability of the fungicide carbendazim for selective inhibition ofH. rhossiliensis in peach orchard soil. The effect of carbendazim (methyl benzimidazol-2-ylcarbamate; DPX 965-50DF; 50% a.i.; E. I. DuPont DeNemours and Co., Wilmington, DE) on sporulation of H. rhossiliensis was examined. Hirsutella rhossiliensis-colonized ,C. xenoplax from naturally infested orchard soil were transferred individually to 1.5% water agar amended with 0, 1, 2, 10, or 100 mg a.i. carbendazim/liter and incubated at 22 + 2 C (the incubation temperature for all experiments). After 5 days, most nematodes on water agar supported sporulation o f /4 . rhossiliensis, but no sporulation occurred from nematodes on carbendazim agar (Fig. 1). Carbendazim was fungistatic because sporulation usually occurred if nematodes