There is a current need to develop alternative weed management techniques in response to demands for reduction in herbicide use due mainly to health and environmental concerns. Therefore, all possible nonchemical strategies for weed control should be considered, including biological control. Deleterious rhizobacteria (DRB), largely overlooked as potential biological control agents for weeds until recently, are able to colonize root surfaces of weed seedlings and suppress plant growth. Limited field studies indicate that DRB suppressed weed growth, and reduced weed density, biomass, and seed production. In this manner, crops out-compete the suppressed weeds for growth requirements, eliminating the necessity for eradication of weeds in the crop. Establishment of DRB as a viable biological control strategy initially will require integration with other weed control approaches including other biocontrol agents, agrichemicals, and cultural and residue management practices. To achieve success, more in-depth research is needed on ecology of bacteria-plant relationships, mechanisms of action (including characterization of phytotoxins), inocula formulations, and methods to enhance crop competition.

The postemergence herbicide ethofumesate and the plant growth regulator paclobutrazol were evaluated for annual bluegrass control in creeping bentgrass turf managed as golf fairways. Both products were applied under several different timing regimes relative to the time of the year. Paclobutrazol treatments provided significantly greater annual bluegrass control than ethofumesate. There were no differences between rates of paclobutrazol (0.28 and 0.14 kg ai/ha) when applied from spring through summer. Annual bluegrass control after spring and summer applications of paclobutrazol was 85% or more. Clipping weight data indicated that paclobutrazol suppressed growth in annual bluegrass longer than in creeping bentgrass. It was concluded that prolonged suppression of annual bluegrass by paclobutrazol resulted in creeping bentgrass dominance and subsequent annual bluegrass control. Additionally, applications of ethofumesate in autumn–winter, followed by paclobutrazol applied in spring–summer, provided significant control of annual bluegrass in 1 yr of the study.

Prohexadione calcium is an experimental turfgrass growth regulator that selectively controls or suppresses annual bluegrass in desirable turfgrass such as creeping bentgrass, Kentucky bluegrass, and perennial ryegrass. To help explain interspecific differences in turfgrass and weed response to prohexadione calcium, two laboratory trials were conducted to measure 14C-prohexadione calcium absorption, translocation, and metabolism in these four species. Annual and Kentucky bluegrass absorbed more prohexadione calcium than creeping bentgrass and perennial ryegrass when averaged over harvest timing and trial. Radioactivity partitioning to other foliage did not differ between species but annual bluegrass and Kentucky bluegrass translocated more radioactivity to roots and evolved more radioactive CO2 than creeping bentgrass and perennial ryegrass. Thin-layer chromatographic separations indicate radioactivity was translocated predominately as prohexadione calcium. When averaged over species and trial, 25 and 16% of recovered prohexadione calcium was metabolized within 1 h after treatment in treated leaves and other foliage, respectively. The rate of metabolic degradation was 0.7% h−1 in treated leaves and 0.4% h−1 in other foliage. Previous research indicates that annual and Kentucky bluegrass growth is suppressed more by prohexadione calcium than is growth of creeping bentgrass and perennial ryegrass. Increased prohexadione calcium absorption partially explained these interspecific differences in growth suppression.