Giant rat’s tail

The Problem with Giant rat’s tail grass

Like other weedy sporobolus grasses, Giant rats tail grass is an aggressive competitor that can reduce pasture productivity and will significantly degrade natural areas. Flowering plants are long-lived and can exist for more than 4 years. Their foliage has low palatability for animals when mature and is therefore not selectively grazed. GRT is resistant to fire, slashing, grazing and high competition. However, it is sensitive to some herbicides.

Seed is produced all year around, but mostly in summer and autumn. A large soil seed bank forms quickly and seeds can live dormant in the soil for approximately 8 years.

Giant rat’s tail grass (GRT) grows to an average maximum height of between 1.7-2m, with the seed head growing to 45cm long and 3cm wide. These seed heads are often darker coloured and change from a rats tail shape to an elongated pyramid shape. They can be difficult to differentiate from other pasture grasses before maturity. Giant rats tail leaves are noticeably tougher than other sporobolus grasses. Native sporobolus grasses tend to be shorter, softer and have less dense seed heads than GRT grass.

Weedy sporobolus grasses are aggressive, have low palatability when mature, and are difficult to control. They can quickly dominate a pasture, especially following overgrazing or soil disturbance. Giant rat’s tail grass (GRT) poses a significant threat to the productivity of pastures in the Mackay Whitsunday Isaac region. GRT is one of the weedy sporobolus grasses (WSG) with the ability to significantly decrease grazier’s economic viability and degradation of natural areas. Cattle grazing GRT pasture take up to 12 months longer to reach equivalent weight. In 2007 the estimated cost of GRT and other WSG to the pastoral industry was $60 million per year (Bray and Officer 2007).

Seed germination and emergence requires an area of low competition, where pasture and other plants have been disturbed and a gap exists. Good pasture cover reduces emergence. Seeds can germinate all year round, but mostly in spring and summer.

The survival of early seedlings is sensitive to competition. Seedlings can flower within three months. Attempts to control this weed using conventional methods have often failed and, in some cases, intensified the infestation. Pastures dominated by GRT are common, due to the long-term viability of GRT seed in the soil and the tendency of stock to graze other more palatable pasture before GRT.

Bray, S. and Officer, D., 2007, Weedy Sporobolus grasses Best Practice Manual, Department of Primary Industries and Fisheries, Brisbane