Evaluation of Curvularia intermedia (Cochliobolus intermedius) as a potential microbial herbicide for large crabgrass (Digitaria sanguinalis)

Curvularia intermedia, anamorph of the fungus Cochliobolus intermedius, was isolated from diseased crabgrass (Digitaria sp.) plants and evaluated in greenhouse studies for its potential as a microbial herbicide for control of large crabgrass (Digitaria sanguinalis). The objectives were to evaluate the host range of the fungus and to determine mortality and dry-weight reductions of large crabgrass as influenced by concentrations of inoculum and Silwet L-77 (an organosilicone surfactant), post-inoculation dew temperature, and post-inoculation dew duration. In addition, control of large crabgrass growing in mixed stands with soybeans was evaluated. Ninety to 100% control of large crabgrass, as indicated by mortality and dry-weight reduction, was obtained when inoculum concentrations were greater-or-equal, slanted1×106 conidia/ml, Silwet L-77 concentrations were greater-or-equal, slanted0.1% (v/v), and dew periods were greater-or-equal, slanted10 h (20–35 °C). Forty plant species in 10 families were screened against C. intermedia in host-range studies. Species that exhibited mortality and/or significant dry-weight reductions due to fungal inoculations included: redroot pigweed (Amaranthus retroflexus), beet (Beta vulgaris), chenopodium (Chenopodium amaranticolor), wild oat (Avena fatua), broadleaf signalgrass (Brachiaria platyphylla), bermudagrass (Cynodon dactylon), large crabgrass, barnyardgrass (Echinochloa crus-galli), red rice (Oryza sp.), green foxtail (Setaria viridis), shattercane (Sorghum bicolor), johnsongrass (Sorghum halepense), one cultivar of grain sorghum (Sorghum vulgare), and two cultivars of corn (Zea mays). No mortality or significant dry-weight reductions were noted for peanut (Arachis hypogaea), soybean (Glycine max), cotton (Gossypium hirsutum), centipedegrass (Eremochloa ophiuroides), St. Augustinegrass (Stenotaphrum secondatum), zoysiagrass (Zoysia sp.), or 23 other species. When C. intermedia was applied to mixed plantings of soybeans and large crabgrass, 80–96% reductions in dry weight occurred for large crabgrass seedlings. No significant dry-weight reductions were observed for the soybean plants when compared to the control plants. These results indicate that C. intermedia could be a potential microbial herbicide for control of large crabgrass in crops such as soybean, cotton, and peanut. Additional studies are needed to assess the potential for use of C. intermedia for control of Digitaria spp. in turf grasses such as centipedegrass, zoysiagrass, and St. Augustinegrass that exhibited resistance to the fungus.