Author
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Bruck, Denny |
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Submitted to: Biological Control
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/15/2004 Publication Date: 1/3/2005 Citation: Bruck, D.J. 2005. Ecology of Metarhizium anisopliae in soilless potting medium and the rhizosphere: implications for pest management. Biological Control. 32:155-163. Interpretive Summary: Wholesale container-grown ornamentals are subject to infestation by black vine weevil (BVW)for several months each year. Plants are often maintained at the nursery for at least two growing seasons before sale. Therefore, a potting medium amendment aimed at controlling BVW needs to persist for an extended period of time. These studies were conducted to determine the persistence of the insect-killing fungus, Metarhizium anisopliae, incorporated into peat and bark-based potting mediums in container-grown spruce. Rooted cuttings of spruce were planted into potting medium incorporated with M. anisopliae (1 g of formulated product/L potting medium) with and without crab meal ammendment. The fungal population in the bulk potting medium was determined at 14, 21, 28, 35, 49, 63, 77, 91, 105, 119, 143, 175, 203, 231, 258, 287, and 342 d. The fungal population in the soil surrounding the roots was quantitatively determined at 203, 231, 258, 287, and 342 d. The M. anisopliae population in the soil surrounding the roots was significantly greater than in the other areas of the pot. Metarhizium anisopliae persisted in the peat and bark-based potting mediums at populations great enough to provide over 93% control of last instar BVW. Spruce roots treated with M. anisopliae infected 76% of 2nd-3rd instar BVW. The ability of treated roots to serve as a delivery system for M. anisopliae represents a new method for delivering biological control agents, and would greatly reduce the cost of application. Technical Abstract: These studies were conducted to determine the persistence and ecology of the entomopathogen, Metarhizium anisopliae, incorporated into peat and bark-based potting mediums in container-grown Picea abies 'Nidiformis'. Rooted cuttings of P. abies were planted into potting medium incorporated with M. anisopliae (1 g of formulated product/L; ~ 6 log10 cfu/g dry potting medium) with and without a crab meal amendment. The fungal population in the bulk potting medium was quantitatively determined using selective media at 14, 21, 28, 35, 49, 63, 77, 91, 105, 119, 143, 175, 203, 231, 258, 287, and 342 d. The fungal population in the rhizosphere soil was quantitatively determined at 203, 231, 258, 287, and 342 d. Metarhizium anisopliae colonized the rhizosphere of P. abies, and the fungal population in the rhizosphere soil was significantly greater than in the surrounding bulk soil. Metarhizium anisopliae persisted in the peat and bark-based potting mediums at 6.22 and 5.74 log10 cfu, respectively, 342 d after incorporation. Bioassays using bark and peat-based potting mediums inoculated with M. anisopliae at 6 log10 cfu/g dry potting medium resulted in 93.5 and 97.5% infection, respectively, of last instar black vine weevil (BVW), Otiorhynchus sulcatus F. Roots of P. abies inoculated with M. anisopliae as a sole source of inoculum infected 76% of 2nd-3rd instar BVW. The ability of inoculated roots to serve as a delivery system for M. anisopliae represents a new method for delivering entomopathogens and would greatly reduce application costs. When selecting an isolate, an understanding of the factors associated with the entomopathogen's biology outside of the host may be more important than the entomopathogen's virulence in a laboratory bioassay. |
