Dear Envirocare Coordinators, Go Green Champions, and Eco Explorers,

This month, we shed light on the weed flora. Flora (plant life) and fauna (all animal life) are two forms of life that coexist along with other life forms, and their symbiotic relationship makes Nature one. The oxygen that we breathe in comes from all plants, including weeds, and the carbon dioxide we exhale is vital for the flora. Have you ever wondered what makes a plant a weed? Very often, we decide to pull, hoe, or treat weed problems only to see it growing at full strength the next day.  

Weeds are rampant and creep into our gardens, fields, parks, roadsides and on almost all bare land.

Weed growth is in fact Nature’s way of protecting itself. If the soil is bare, then it is hungry of nutrients and is vulnerable to erosion or degradation. This flush of weeds will cover the bare soil as a healing response to land disturbance after either natural disasters or human activities.¹

Ever since the cultivation of plants, humans had to fight the invasion by weeds into areas chosen for crops. Some unwanted plants were found to have virtues not originally understood and so these were removed from the category of weeds and instead taken under cultivation. Other cultivated plants, however, when transplanted to new climates, escaped cultivation and became weeds or invasive species. 

Many weed species are potentially toxic² and, if found in pastures and crops, present a realistic threat to animals.

The Sri Sathya Sai International Organization of Kenya, Zone 9, initiated the Parthenium pull-out project in March 2021. Parthenium weeds (scientific name: Parthenium hysterophorus L., family: Asteraceae) are fast spreading in Kenya where they have been spotted in coffee plantations around Kiambu and Nyeri districts, around Nairobi, Kajiado and Naivasha.³ Devotees of the Sri Sathya Sai Centres of Nairobi and Mombasa in Kenya together with the young people of Stand Up Shout Out (SUSO, a non-governmental organisation) and friends of Nairobi Park collaborated with great enthusiasm to remove these dangerous and poisonous parthenium weeds from some areas of Nairobi Park. This clean-up activity has already been organised four times with different team members and around 500 kg of Parthenium weeds have been pulled and discarded.

Parthenium weed is toxic to animals, causing dermatitis with pronounced skin lesions on some animals, including horses and cattles. If eaten, it is responsible for mouth ulcers with excessive salivation.⁴ This weed species is included in the Global Invasive Species Database (GISD 2022)⁵ and is listed as a prohibited plant that must be controlled.

Parthenium weed has now invaded more than 20 countries around the globe, including five continents and numerous islands.⁴ Parthenium weed produces enormous amount of pollen (on average 624 million/plant), which is carried over short distances in clusters of 600–800 grains and settles on vegetables like tomato, brinjal, beans, capsicum and maize, and also on floral parts of plants.⁴ The pollen grains, airborne dried plant parts, and roots of parthenium cause various allergies, like contact dermatitis, hay fever, asthma and bronchitis in human beings.⁴ Parthenium weeds compete severely with other plants for water and nutrients through their extensive root/rhizome systems,¹ and can cause yield decline of up to 40% in agricultural crops⁴ or can even wipe an entire field. 

Allelopathy is a chemical process that a plant uses to keep other plants out of its vicinity.⁶ Under appropriate conditions, the weeds release allelochemicals in sufficient quantities into the region of soil surrounding the plant roots, known as the rhizosphere, to affect the neighbouring plants.⁷

The seeds are small and light enough to be blown by the wind over short distances and can sometimes survive for decades in the soil.⁸ They sprout just as soon as conditions are right. Manual uprooting of the invasive parthenium weeds before flowering and seed setting is the most effective method of protecting biodiversity.⁴

VISIT the Environmental Sustainability Hub for more insights, go green tips and resources

With Sai Love and Care,

Environmental Sustainability Committee 

Sri Sathya Sai International Organization

^{1 Mark Schonbeck, Virginia Association for Biological Farming. An Ecological Understanding of Weeds.}

^{2 Birgit Puschner, Amy Peters, Leslie Woods. Toxic weeds and their impact on animals.} 

^{3  Fact sheet adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland.}

^{4 Manpreet Kaur, Neeraj Kumar Aggarwal, Vikas Kumar and Romika Dhiman. Academic Editor: Suhel Parvez. Effects and Management of Parthenium hysterophorus: A Weed of Global Significance by Kurukshetra University, Kurukshetra, Haryana 136119, India.}

^{5 Global Invasive Species Database (2022).} 

^{6 A. Amin, H. Rahsid, M.A. Khan, and M.I. Khan. Allelopathic effects of Parthenium hysterophorus (L.) Extracts on Seed Germination and Growth of Wheat and Associated weeds.}

^{7 Leslie A. Weston. Utilisation of Allelopathy for Weed Management in Agroecosystems, 1996.}

^{8 Don Morishita, Ph.D., the Weed Science Society of America.}