Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 24, 2011
Publication Date: January 15, 2012
Citation: Boyette, C.D., Bryson, C.T., Hoagland, R.E., Weaver, M.A. 2012. Effects of simulated rainfall on disease development and weed control efficacy of the bioherbicidal fungi Alternaria cassiae and Colletotrichum truncatum. Weed Technology. 26:117-121. Interpretive Summary: Rainfall wash-off reduces the effectiveness of many chemical pesticides, as reported in simulated rainfall studies, but few studies have examined effects of simulated rainfall on the efficacy of fungi to control weeds (bioherbicides). A rainfall simulator that reproduced natural rain events was used to examine effects of three durations of rain at various times after application of the fungi Alternaria cassiae and Colletotrichum truncatum for control of sicklepod and hemp sesbania, respectively, under greenhouse conditions. Control of sicklepod by A. cassiae, was relatively unaffected by rain amounts or timings (85-100%), regardless of dew delay. Control of hemp sesbania by C. truncatum was highest when plants received no rainfall with an immediate dew treatment. Hemp sesbania control was reduced by 60% when dew was delayed by even 1 h after inoculation. A 4 h delay in dew resulted in weed control no better than in untreated controls. These results indicate that effects of rainfall vary greatly on weed control among bioherbicides and the sensitivity to dew among these fungi.
Technical Abstract: Alternaria cassiae and Colletotrichum truncatum are virulent pathogens of sicklepod (Senna obtusifolia), and hemp sesbania (Sesbania exaltata), respectively, under favorable environmental conditions. In greenhouse experiments, the effects of simulated rainfall on pathogenesis and mortality of these weeds were examined using a rainfall simulator apparatus that reproduced water droplet size, velocity, and kinetic energy analogous to natural rainfall. With A. cassiae little differences occurred between rainfall amounts or timings upon pathogenesis or weed control efficacy of sicklepod, with 85-100% control occurring within 8 d, regardless of dew treatment. With C. truncatum, pathogenesis and mortality of hemp sesbania were significantly greater in plants that received no rainfall followed by an immediate dew treatment. However, regardless of rainfall amounts, disease development and mortality of hemp sesbania were greatly reduced (60%) when dew treatment was delayed by 1 h following inoculation, regardless of rainfall treatments. A 4 h delay in dew treatment was not significantly different than untreated controls. These results indicate that effects of rainfall vary greatly on pathogenesis and weed control between mycoherbicides.