The highly competitive, adaptable and allergenic weed Parthenium hysterophorus
(Composite) is an invasive annual weed believed to be introduced to Ethiopia in 1970s. Field surveys, plant biodiversity impacts, and analysis of secondary plant compounds in P. hysterophorus and its possible impact on human health have been studied in Ethiopia since 1998. The weed has invaded a variety of habitats ranging from roadsides to grasslands and crop fields. Infestations were found to be greater than 20 plants per m2 and yield losses in sorghum reached 46-97% depending on the location and year. In grasslands dominated by parthenium, native plant species composition and abundance was found to be low. Manual control of parthenium by farmers resulted in the development of skin allergies, itching, fever, and asthma. These reactions could be attributed to the presence of secondary plant compounds (parthenin, chlorogenic acid, isocholorogenic acid, vanilic acid and caffeic acid) which were found in parthenium with significant variation in their concentrations among the different plant parts, dependent on plant locality, moisture content and plant size. The social cost of parthenium in Ethiopia was measured by Disability Adjusted Life Years and its equivalence in terms of monetary value was estimated at US$ 2,535,887 - 4,365,057. More resources have to be invested to tackle the parthenium problem as the estimated loss is disproportionate to the cost of investment in parthenium research and development activities.
