Weed Seed in Horse Dung

August 9, 2023

A paper by Michael Ansong and Catherine Pickering details a global review of literature on the subject of weeds that can germinate from horse dung. ( Ansong, M. and Pickering, C. (2013), A global review of weeds that can germinate from horse dung. Ecological Management and Restoration, 14:216-223)

“Seed from 249 species from 43 families have been identified germinating from horse dung. Almost two-thirds of the species were forbs and 33% graminoids (grasses), with over half being perennials and 32% annuals. Nearly every species (totalling 99% of those reviewed) is considered a weed somewhere, with 47% recorded as invasive and 19% as international weeds.” The appendix to Ansong and Pickering’s paper details these 249 species.

“Of the 2739 non-native plants that are naturalised in Australia, 156 have been shown to germinate from horse dung. This includes 16 of the 479 listed noxious weeds in Australia and two weeds of national significance. Seed traits including seed size, length, width and mass affect seed dispersal via horse dung. Habitat disturbance from trampling facilitates germination of seedlings. The diversity of species with seed that can germinate from horse dung highlights the potential of horses to disperse a range of seed over long distances”

”Several studies have found large amounts of viable seed in horse dung, with estimates of … 500,000 viable seeds produced per horse per year. Horse riding can spread seed on fur, hooves, riders, equipment and feed as well as in dung.”

This study highlights the potential for weed-spread into environmental protected areas, especially where trails skirt the edge or pass through such areas, for example the Mylor Conservation Park.

Horse SA has produced a range of publications regarding hygiene with respect to weed seeds and also Phytophthora, the plant-pathogenic, subterranean fungus, or more correctly, a water mould.

For the bushcare worker or property owner with bushland, many of the weeds spread by horses pose various levels of threat and inconvenience often taking valuable time away from dealing with the many other weeds that bushland is subject to. The 249 weed species mentioned above contains many grasses ( Poaceae family ), medics ( Medicago sp.), clovers ( Trifolium sp.) and rushes ( Juncus sp. ). Others of local interest include:-

– bedstraws ( Gallium sp. );
– blackberry nightshade ( Solanum nigrum );
– common chickweed ( Stellaria media );
– common plantain ( Plantago lanceolatum );
– daisies such as smooth cat’s ear ( Hypochaeris glabra ) and dandelion ( Taraxacum officinale );
– docks ( Rumex sp. );
– fat hen ( Chenopodium album );
– horehound ( Marrubium vulgare );
– shepherds purse ( Capsella bursa-pastoris );
– St John’s wort ( Hypericum perforatum );
– wild onion ( Asphodelus fistulosis ).
– wireweed ( Polygonum aviculare ).

Note that wild onion is not the white-flowered 3-cornered garlic (Allium triquetrum). Both Asphodelus and Allium are, confusingly, called ‘onion weed’ in various parts of the Adelaide Hills.