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Host Range Determination of Myrothecium verrucaria Isolated from Leafy Spurge. Shaw-ming Yang, Research Plant Pathologist, U.S. Department of Agriculture, Foreign Disease-Weed Science Re-search Unit, Ft. Detrick, Bldg. 1301, Frederick, Md. 21702. S. C. Jong, Head, Department of Mycology, ATCC, Rockville, Md. 20852. Plant Dis. 79:994-997. Accepted for publication 10 May 1995. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1995. DOI: 10.1094/PD-79-0994.

The host range of Myrothecium verrucaria (ATCC 90310) isolated from leafy spurge (Euphorbia esula) collected in China was determined to be 54 plant species in 42 genera and 11 families following artificial inoculation. The number of plant species infected was influenced by the dew temperature or invert emulsion (IE, water-in-oil) carrier for the inoculum. Of 46 plant species inoculated with an aqueous conidial suspension and incubated for 18 h in dew chambers at 15, 20, 25, and 30C, 1, 6, 15, and 39 plant species, respectively, developed disease. Velvetleaf (Abutilon theophrasti) was killed by this pathogen only when the plants were inoculated with IE carrier plus conidia, but not when atomized with an aqueous conidial suspension and incubated in dew chambers at 30C for 18 h. Disease severity on thistle (Carduus spp.) and starthistle (Centaurea sp.) was greatly affected by the use of the IE carrier; high inoculum levels of M. verrucaria were needed lo kill older thistle plants. Myrothecium verrucaria has potential as a mycoherbicide against annual weeds.