When formulated and sprayed in an invert emulsion (IE), conidia of the
mycoherbicide, Colletotrichum truncatum, controlled hemp sesbania in
the absence of dew. To optimize hemp sesbania control, formulation dro
plet size influence upon the pathogen's germination and pathogenicity
was investigated. Conidia germination in manually produced IE droplets
decreased from 46% to 5% as droplet diameter decreased from 2700 to 9
00 mum. Droplet size did not affect appressoria formation. On a per co
nidium basis, 900-mum droplets were more pathogenic to detached hemp s
esbania leaves than were 2100-mum droplets. An air-assist spray system
produced droplet spectra with volume median diameters of 421 and 104
mum, respectively. The spectrum of smaller droplets covered the target
better than did that of larger droplets. When applied to whole hemp s
esbania plants in greenhouse trials, conidia in the smaller and larger
droplet spectra gave 90 and 94% control, respectively. Sufficient con
idia germinated in IE droplets of a variety of sizes to control hemp s
esbania excellently.