The first record of milk thistle (Silybum marianum, Asteraceae) as an alien invasive weed species in Addis Ababa City, Ethiopia.

Abstract

Since 2020, milk thistle Silybum marianum, an invasive weed species, has been widely observed in urban green spaces and roadsides in Addis Ababa city, Ethiopia. To plan future management activities, this study aimed to determine the current distribution status of the weed in urban green areas of Addis Ababa city. Weed surveys were conducted across 42 urban green sites located in Yeka, Lemi Kura, Bole, Nifas Silk-Lafto, Kolfie Keraniyo, Akaky Kality, and Gullele sub-cities during the main rainy season from June to September 2023. Urban green areas were selected using purposive sampling techniques. Field observations confirmed that Silybum marianum can invade and colonize a wide range of habitats and is highly competitive, posing a threat to important native plant species. High weed density rates and dense stands of weeds were recorded in the 34 urban green areas surveyed. The survey results strongly suggest implementing fast integrated weed management options such as mowing/tilling, weeding before the plant goes to seed, cutting (stems and/or seed heads), and burning (collected plant parts and/or seed heads) into a prepared burrow to minimize the spread of the weed and its ecological impacts. The purpose of this survey study is to provide information about Silybum marianum to minimize or avoid its distribution and associated impacts by following sustainable invasive weed management programs in the city before spreading to other cities in the country.