Impact of fungicides on Metarhizium anisopliae in the rhizosphere, bulk soil and in vitro

Abstract

The entomopathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) is registered in the United States and The Netherlands for black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) control in container-grown ornamentals. These studies were conducted to determine the compatibility of M. anisopliae (F52) with a wide range of fungicides commonly applied to container-grown ornamentals for the management of soil-borne plant pathogens. The impact of fungicides on spore germination and mycelial growth were determined in vitro. In addition, M. anisopliae persistence in bulk and rhizosphere soil was determined 30 days following dual application of each fungicide at 7-28 days intervals as prescribed. A number of fungicides (thiophanate-methyl, dimethomorph, captan, triflumizole, triflozystrobin, pyraclostrobin, azoxystrobin) inhibited spore germination in vitro. A larger number of fungicides (fosetyl-AI, thiophanate-methyl, dimethomorph, captan, quintozene, triflumizole, fludioxanil, triflozystrobin, pyraclostrobin, fludiox-mefanox, iprodione, azoxystrobin, phosphorus acid/K-salts) inhibited mycelial growth in vitro. Only three fungicides (etridiazole, propamocard and mafanoxam) had no significant impact in vitro on spore germination or mycelial growth. While a number of fungicides had a detrimental impact in vitro, there was no impact on M. anisopliae populations in bulk soil following dual application of any fungicide. However, the fungicides captan and triflumizolet, which have a short reapplication interval, had a detrimental impact on M. anisopliae populations in the rhizosphere. As researchers develop rhizosphere competence as an alternative management strategy for black vine weevil, the fungicides captan and triflumizole should be avoided.

Compatibility of the Entomopathogenic Fungus Beauveria bassiana with Some Fungicides Used in California Strawberry

“…Shah et al [12] reported variation in the inhibitory effect of the fungicides on different fungi. While captan appears to be detrimental to multiple entomopathogenic fungi, strobilurin fungicides, azoxystrobin and pyraclostrobin seem to be compatible with B. bassiana, but not with Metarhizium spp [9,12].…”

“…Sulfur and captan are the most widely used fungicides and in general, fungicide use surpasses that of acaricides and insecticides in California strawberries [2]. Earlier studies by Moorhouse, Gillespie, Seller, and Charnley [6], Jaros-Su, Groden, and Zhang [7], Luz, Netto, and Rocha [8], and Brook [9] evaluated the impact of some fungicides on the fungal growth and pest control efficacy of B. bassiana or other entomopathogenic fungi through invitro or potted plant studies in multiple crop or pest situations. However, no information specific to the fungicides used in California strawberries is available, especially after the release of some new fungicides in the recent years.…”

Natural and released inoculum levels of entomopathogenic fungal biocontrol agents in soil in relation to risk assessment and in accordance with EU regulations

“…Only three fungicides (etridiazole, propamocard and mafanoxam) had no significant impact in vitro on spore germination or mycelial growth. Bruck (2009) found that, although a number of fungicides had a detrimental impact in vitro, most had no impact on M. anisopliae populations in bulk soil. The only exceptions were captan and triflumizolet, which had a detrimental impact on M. anisopliae populations in the rhizosphere.…”

Ecological factors in the inundative use of fungal entomopathogens

“…Often the best, most realistic approach is within the context of a field trial or at least outdoor, in-field microcosm. For instance, it was demonstrated that of 13 fungicides toxic in vitro, none had adverse impact on M. anisopliae in commercial potting media under realistic conditions, even when applied twice during the observation period (Bruck 2009a).…”