- Widespread. Asia, Africa, North, South and Central America, Caribbean, Europe (restricted), Oceania. In most Pacific countries.
- Aggressive weed, particularly invasive in pastures and woodland-grasslands, but also in plantations, including forestry, cereal, root and vegetable crops, lawns, along waterways, in waste land and roadside. Prolific seed production over many different soil types, especially where environments are seasonally wet or dry. Cattle avoid the weed.
- Erect, branched, perennial shrub, 30-100 cm tall, woody stem, and long, tough taproot. Leaves, spear-shaped, saw-like margins, alternate along stem, with hairy leaf stalks. Flowers, light yellow to orange, five petals, and many stamens. Fruit, brown, hard, containing 5-8 wedged-shaped parts, each with two stiff bristles, and a seed inside.
- Spread: seed; fur of animals; vehicles; clothing; water; and as contaminant of hay.
- Biosecurity: high risk of introduction; One of the worst 10 weeds in New Caledonia, Solomon Islands and Vanuatu.
- Biocontrol: introduction of Calligrapha pantherina - Australia, Fiji, PNG, Vanuatu.
- Cultural control: dig or grub out, or plough, disc, harrow (before seed set), and repeat, or cultivate, then sow dense grass and legume pasture; avoid over-grazing pasture (maintain healthy growth); vehicle hygiene to remove seed.
- Chemical control: in Australia (pre-emergence): imazethapyr; pendimethalin; or imazapic; (post-emergence): imazethapyr; 2,4-D; fluroxypyr; or dicamba. In Fiji, glyphosate.
Pacific Pests, Pathogens, Weeds & Pesticides
Sida; it is also known as spinyhead sida, broom weed.
Sida acuta. It was known previously as Sida acuta subspecies carpiunifolia and Sida carpinifolia. It is a member of the Malvaceae.
There are a number of Sida species, with Sida rhombifolia common in the region. It is recorded in all those countries listed for Sida acuta, plus Tokelau, and Wallis and Futuna.
AUTHORS Grahame Jackson, Aradhana Deesh & Mani Mua
Adapted from Spinyhead weed (Sida acuta) (2018) Weeds of SE Qld and Northern NSW. Lucidcentral. (https://play.google.com/store/apps/details?id=com.lucidcentral.mobile.sew_full&hl=en_AU&gl=US); and CABI (2019) Sida acuta (sida). Invasive Species Compendium. (https://www.cabi.org/isc/datasheet/49985); and Sida acuta Burm.f. (2011) Weeds Australia - profiles. (https://profiles.ala.org.au/opus/weeds-australia/profile/Sida%20acuta); and DPI&RD (2020) Sida: pest. Agriculture and Food. Government of Western Australia. (https://www.agric.wa.gov.au/declared-plants/sida-pest); and from Waterhouse DF, Norris KR (1987) Sida acuta. Biological Control Pacific Prospects. Inkata Press, Melbourne;
Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland, in association with the Pacific Community and Koronivia Research Station, Ministry of Agriculture, Fiji.