Mulatu Wakjira

Cover crops as a means of ecological weed management in agroecosystems

Weeds cause an estimated crop yield loss of about 43% world-wide. The heavy use of herbicides in weed management has several environmental and health risks. Therefore, systems-oriented approaches to weed management that make better use of alternative weed management tactics need to be developed. One of these approaches is the use of plants with strong weed-suppressing abilities as a component of integrated crop management. Cover crops are well-suited in such a holistic approach as they provide many other agroecosystem services besides suppressing weeds. However, compared to the use of herbicides, the use of cover crops as a weed management tool needs careful follow-up throughout the intended period to maximize the agroecosystem services they provide, minimize the disservices they exert, and optimize their selectivity between weed and crop suppression. Although there are many review papers that address the contribution of cover crops for managing weed problems in agroecosystems, few systematically address the difficulties that are encountered in fitting in the cover crops in the different cropping systems and the methods how to overcome these difficulties. Therefore, this paper is to examine how to maximize weed suppressive effects of cover crops and minimize the negative side effects of introducing cover crops into annual and perennial cropping systems and how to optimize selectivity between weeds and crops. We suggest further research regarding the selection of cover crops that are compatible with annual and perennial cropping systems under different climatic conditions and identify the traits responsible for adaptation in various cropping systems and environments.

An invasive alien weed giant sensitive plant (Mimosa diplotricha Sauvalle) invading Southwestern Ethiopia

Cross sectional study was conducted in Jabi Tehenan district of West Gojjam administrative zone from October 2008 to April 2009 to determine the current prevalence rate of bovine trypanosomosis. In the parasitological survey, blood samples of 300 cattle were examined using a buffy coat technique. The PCV value of each animal was also measured using hematocrit reader. The overall prevalence of trypanosomosis was found to be 11.7% and it consists of 16, 10 and 9% in Regeb Kebero Meda, Weyenema Workema and around Finote Selam peasant associations, respectively. The most positive cases were due to T. congolense (54.3%) followed by T.vivax (45.7%). The mean PCV value (%) of parasitaemic and a parasitaemic animals during the study period were 20.3 ± 4.1 SD and 25.29 ± 4.67 SD with a significance difference (P<0.05). The study also demonstrated variations in prevalence among different age groups and between both sexes which were statistically insignificant. Infection rate in poor body condition animals were significantly higher than good body condition animals (P<0.05). The present prevalent study generated valuable information on the epidemiology of bovine trypanosomosis in the study area and revealed that trypanosomosis is an important disease in the study area.Crude extracts of wild cucumber (Cucumis myriocarpus) fruits have been successfully used as postemergent bio-nematicide in suppression of the southern root-knot nematode (Meloidogyne incognita). Compatibility of this bio-nematicide with plant growth when used as a pre-emergent bionematicide was tested on onion (Allium cepa), leek (Allium ampeloprasum) and chive (Allium schoenoprasum) under greenhouse conditions. In each trial, 10 levels of crude extracts of C. myriocarpus fruits were arranged in a randomised complete block design, with five replicates. At harvest, 18 days after planting, seedling height, radicle length, coleoptile length and coleoptile diameter each were each subjected to the Curve-Fitting Allelochemical Response Data (CARD) model, which demonstrated that at both low and high levels, the bio-nematicide had stimulatory and inhibitory effects on growth of test plants, respectively. The total sum of transformations (�k), expresses the sensitivity of the test plant to the bio-nematicide, �k being inversely proportional to the degree of sensitivity. Overall, onion was the most sensitive to the bio-nematicide, followed by chive and leek. In conclusion, since the material had 100% inhibition of plant growth where it suppresses nematodes, the material is not suitable for use as a pre-emergent bio-nematicide.

Antifungal activity of some invasive alien plant leaf extracts against mango (Mangifera indica) anthracnose caused by Colletotrichum gloeosporioides

The antifungal activity of five invasive alien plant leaf extracts against Colletotrichum gloeosporioides was studied in vitro and in vivo. The in vitro antifungal activity was based on the inhibitory effects of the extracts on C. gloeosporioides radial growth and conidia formation, while the in vivo activity was based on the development of anthracnose disease on detached mango fruits. For the in vivo test, two plant extracts that showed higher inhibitory effect in vitro were selected and their minimum inhibitory concentrations were determined and tested against the disease on detached mango fruits applying the extracts at three times of application. The study revealed that the inhibitory effect of the extracts depends on the type of plant species used, method of extraction and time of application of the extracts. Prosopis juliflora and Lantana camara extracts were the most effective plant extracts that significantly reduced radial growth and conidia formation, and reduced disease development on mango fruits. Thus, P. juliflora and L. camara extracts can serve as an alternative means of post-harvest mango anthracnose disease management.

Inhibitory effects of some invasive alien species leaf extracts against tomato (Lycopersicon esculentum Mill.) bacterial wilt (Ralstonia solanacearum)

The inhibitory activity of selected invasive alien species leaf extracts against tomato bacterial wilt was studied in vitro and greenhouse. In vitro inhibitory activity was undertaken in a disc diffusion sensitivity test. Furthermore, aqueous extracts of Eichhorina crassipes, Mimosa diplotricha and Lantana camara and methanolic extract of Prosopis juliflora which showed better inhibitory effect in vitro were evaluated against R. solanacearum in greenhouse on tomato. The plant extracts were applied and evaluated at three different times of application (at the time of inoculation; two days before pathogen inoculation; and two days after pathogen inoculation). The result showed that most of the treatment combinations significantly reduce disease incidence and area under disease progress curve and increase biomass of tomato plants, but the effectiveness of tested plant species depends on the type of plant species and application time. The application of plant extracts at the time of pathogen inoculation resulted in highest reduction of disease development on tomato plants. Aqueous extract of E. crassipes was found to be the most effective plant extract in disease suppression and increase above-ground biomass compared to inoculated control. The study revealed that the tested plant species have a potential of inhibiting the development of bacterial wilt on tomato.