Abstract
Greenhouse experiments were conducted to determine the effects of an invert (water-in-oil) emulsion (IE) on dew period duration and dew delay of Colletotrichum coccodes for biocontrol of the problematic weed, eastern black nightshade (Solanum ptycanthum). Dew periods of 4, 8, or 12 h provided 10%, 25%, and 40% control of eastern black nightshade plants, respectively, when C. coccodes (Strain NRRL 15,547) spores were applied in water + Tween 80 surfactant 12 days after inoculation, but a minimum of 16 h of dew was required to achieve ~95% plant mortality. In contrast, at these same intervals of dew, 95%, 100% and 100% mortality occurred, respectively, when fungal spores were formulated in the IE. Even in the absence of dew, 60% mortality and 70% dry weight reductions of plants was achieved with the fungus/IE formulation Delaying dew by 2 h after inoculation did not significantly reduce weed control or plant dry weight reductions when plants were inoculated with the fungus either in the aqueous or in the IE formulation. However, when dew was delayed for 4, 8, or 12 h, only 60%, 50%, and 25% mortality, respectively, of plants receiving the aqueous spore treatment occurred. In contrast, 95%, 90%, and 90% weed mortality occurred after the same dew delays of plants receiving the fungus/ IE treatments. These results demonstrate that formulating C. coccodes spores in an invert emulsion greatly improves the bioherbicidal potential of this fungus. Furthermore, results suggest that this formulation may render pathogens previously rejected for development as bioherbicides due to restrictive dew requirements more efficacious for use in controlling their target weeds.
Highlights
Strategies using plant pathogens as bioherbicides to manage weeds have been examined as demonstrated in several reviews [1]-[10]
Greenhouse experiments were conducted to determine the effects of an invert emulsion (IE) on dew period duration and dew delay of Colletotrichum coccodes for biocontrol of the problematic weed, eastern black nightshade (Solanum ptycanthum)
Dew periods of 4, 8, or 12 h provided 10%, 25%, and 40% control of eastern black nightshade plants, respectively, when C. coccodes (Strain NRRL 15,547) spores were applied in water + Tween 80 surfactant 12 days after inoculation, but a minimum of 16 h of dew was required to achieve ~95% plant mortality
Summary
Strategies using plant pathogens as bioherbicides to manage weeds have been examined as demonstrated in several reviews [1]-[10]. One strategy to reduce lengthy dew requirements of bioherbicidal fungi is the use of selected adjuvants including surfactants, stickers, humectants, and anti-evaporation agents [7] [9] [14]. Previous research in our laboratory and elsewhere has shown that invert (water-in-oil) emulsions and various vegetable oil-in-water emulsions provide a method to retard evaporation and trap water around fungal spores in the spray mixture, thereby decreasing the amount of additional free-moisture (dew) required for spore germination and infection [15]-[21]. We have previously reported greenhouse data that show a 1:1 (v/v) fungus/invert emulsion could reduce the dew period requirements for maximum weed infection and mortality of sicklepod [Senna obtusifolia (L.) H.S. Irwin & Barneby] with the fungus Colletotrichum gloeosporioides (Penz.) Penz. Hill] from 12 h to 2 h, and delayed the need for free moisture for >72 h [18]
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