Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Itch grass (458)

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Relates to: Weeds

Photo 1. Thicket of itch grass, Rottboellia cochinchinensis.

Photo 2. Swollen areas on stems, the nodes, itch grass, Rottboellia cochinchinensis.

Photo 3. Leaves with prominent pale mid-vein, itch grass, Rottboellia cochinchinensis.

Photo 4. Prop roots, itch grass, Rottboellia cochinchinensis.

Photo 5. Rooted prop roots of itch grass, Rottboellia cochinchinensis.

Photo 6. Prominent hairs that cause the itch of itch grass, Rottboellia cochinchinensis.

Photo 7. Flower spike, itch grass, Rottboellia cochinchinensis.

Photo 8. Flower spike, itch grass, Rottboellia cochinchinensis.

Photo 9. Section of the flower spike (called spikelets), containing the seed, itch grass, Rottboellia cochinchinensis.

Summary

• Widespread. Asia, Africa, North, South and Central America, Caribbean, Oceania. In Australia, Fiji, PNG, Solomon Islands.
• Aggressive grass of open, well-drained sites, along roads, railways, but also wet places, including shallow water. Invasive in soybean, corn, cotton, peanut, upland rice, sugarcane. Plants produce many thousands of seeds, and thrive under a range of environmental conditions. Alternative host for maize viruses (Maize mosaic nucleorhabdovirus; see Fact Sheet no. 074). Hairs damage skin.  
• Stems, cylindrical, hollow, branching at upper nodes, with basal prop roots, and multiple tillers. Leaves, blue-green, 5-20 mm wide, with conspicuous pale mid-vein. Silica hairs on leaf sheath cause the itch. Flowers, on spikes, up to 15 cm long, single or in groups of 3-4, arising from leaf axils at top of the stem. As spikes mature, the cylindrical rice-size seeds progressively break free starting at furthest end.
• Spread: seeds, by birds, floodwater, rodents, farm machinery; along transport routes; contaminant of rice and legume seed.
• Biosecurity: high risk of introduction; one of the 12 worst weeds of sugarcane, and a competitive weed of maize. On Global Invasive Species Database of alien invasive species (IUCN, 2020).
• Biocontrol: several fungi have potential as mycoherbicides.
• Cultural control: hand weed; slashing; cultivation (plus use herbicide); interplant food legumes with maize; vehicle hygiene; IPM - fire, plough, fallow.
• Chemical control: in Australia: hexazinone + diuron. In Fiji, glyphosate; diuron.

Common Name

Itch grass

Scientific Name

Rottboellia cochinchinensis; it was known previously as Rottboellia exaltata. It is a member of the Poaceae.

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