Evaluation of botanical herbicides against common Weed species of coffee (coffea arabica l.) With emphasis On bidens pilosa at jimma, southwestern ethiopia

Despite the wealth of genetic diversity, the yield of Ethiopian coffee is low compared with other producer countries. Weeds are one of the most limiting constraints of crop production particularly in organic farming systems, as no herbicides are allowed due to the intent of curtailing their negative impacts on the environments, health and sustainability reasons. Similarly, techniques like mechanical, cultural, biological etc. can be costly and may fail to control weeds adequately. Using natural products, like bioherbicides, are among possible alternatives for weed control in organic farms. Therefore, a series of laboratory, lath-house and field experiments were conducted in 2011/12 at Jimma, Southwestern Ethiopia with the objective of exploring botanical herbicides against common weeds of coffee with emphasis on B. pilosa. The botanical extracts evaluated in the present study consisted of Artemisia annua, Rosmarinus officinalis, Trachyspermum ammi, Cymbopogon winterianus, Eucalyptus citrodora, Eucalyptus globulus, Piper nigrum, Ricinus communis and inert minerals (Diatomate, Bole, and H2O2) combined with concentrations (0.03, 0.06 and 0.09% (v/v)) in CRD for laboratory, application frequency (1x, 2x and 3x) in RCBD with 5% (v/v) concentration for lath-house and field experiments. For comparison, a control and standard check were included and a factorial arrangement was used for all experiments with three replications. In view of that, data were collected on germination, growth and growth parameters of B. pilosa seeds and common weeds of coffee. The results under laboratory revealed that the differences among tested materials were very highly significant (P<0.001) for all parameters studied. The least germination per cent (2%) was obtained as a result of seeds treated with E. citrodora and C. winterianus at 0.09% (v/v) compared to control (98%). Germination rate was fastest for seeds treated with only distilled water (54.42 seeds day-1 ) and the lowest was recorded from C. winterianus (0.16 seeds day-1 ) at 0.09% (v/v). Shoot and root length of B. pilosa were very highly significant (P<0.001) variation. The inhibitory effect of tested materials under lathhouse was not as effective as laboratory experiments. Regardless of these differences, oils extracted from C. winterianus, E. citrodora, R. officinalis and E. globulus revealed consistencies inhibitory effects at both conditions. Essential oils from E. citrodora, C. winterianus and T. ammi also checked their potential herbicides against common weeds of coffee at field trial and the result revealed that highly significant for first two botanicals and no difference for T. ammi related to control for all growth parameters. From these findings, essential oils from E. citrodora and C. winterianus revealed consistent inhibitory effects on growth and growth parameters of weed species at various experimental conditions. Therefore, organic coffee farming systems in Ethiopia may use these oils as alternative means of weed control even though further study needs to be conducted to know the active ingredients inherited from the source plants, mode of action, rate as well as time of application to come up with practical recommendation