In greenhouse experiments, conidia ofColletotrichum truncatumapplied in an invert emulsion formulation controlled hemp sesbania 100% in the absence of a dew treatment. In field experiments, hemp sesbania control averaged 95 and 97% in 1989 and 1990, respectively, when this formulation was applied to hemp sesbania seedlings using tractor-mounted, air-assist nozzles. This level of weed control was comparable to that achieved from the herbicide acifluorfen. These results indicate thatC. truncatumhas excellent potential as a mycoherbicide for controlling hemp sesbania and that this potential can be augmented by formulating the pathogen as an invert emulsion.
Applications of the fungus, Alternaria cassiae Jurair and Khan with and without an overspray of a new experimental invert (water-in-oil) emulsion were evaluated for control of sicklepod (Cassia obtusifolia L.) weed in soybeans ‘Forrest’ with and without a post-treatment dew period under controlled environmental conditions. The unique experimental invert emulsion was developed and applied with specialized air-assist atomizing nozzles as an overspray to provide moisture and to retard evaporation of the water applied so that the fungal spores could germinate and infect the target weeds under relatively dry conditions. Spores applied in an aqueous carrier alone or in an aqueous carrier followed by an overspray of the invert emulsion caused 100 percent mortality by 16 days after treatment if the sicklepod seedlings were exposed after treatment to 18 h of dew. Spores applied in the aqueous carrier alone and in the aqueous carrier followed by an overspray of the invert emulsion caused 0 and 88 percent mortality, respectively, without the dew period. This is the first report known to us of a technique to obtain infection and weed control with a foliar-applied weed pathogen without dew or mist.
The weed sicklepod, a problem in the cultivation of soybean, cotton, and peanut, can be controlled by the mycoherbicide,Alternaria cassiae.However, the presence of water (dew) for an extended period is required by the fungal spores to germinate and infect the target weed. Preliminary tests with invert (water-in-oil) emulsions containing paraffin wax, paraffin oil, lecithin, and water indicated that about 10% (w/w) water, maintained over an 18-h period, was necessary under laboratory conditions for significant germination of the fungus. The ability to maintain that amount of water in the invert emulsion depended upon spray deposit size, adjuvants, and oil phase: water ratio. Paraffin wax was an effective adjuvant for reducing water evaporation and increasing sicklepod mortality in the greenhouse.
An air-assist spray nozzle was constructed to apply herbicides in oil or water at volumes as low as 2.3 L/ha. The spray was metered through a disc orifice inside the nozzle and forced into an airstream which atomized the liquid. The nozzle produced 16 to 54 spray droplets/cm2with air pressures from 3.4 to 62 kPa from a 2-mm outlet using a lightweight paraffinic oil. The number of spray droplet deposits produced with a paraffinic oil at 34 kPa increased from 7 droplets/cm2with a 0.8-mm outlet to 48 droplets/cm2with a 2.4-mm outlet. The nozzle was designed primarily to apply herbicides in oil at 2.3 to 4.7 L/ha, but it has the capability of applying 150 L/ha of oil or water.
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