Managing weeds for wildlife conservation - Guinea Grass Megathyrsus maximus also known as Panicum maximum and Urochloa maxima

Introduction | Impact | Classification | Control | References 

Introduction 

Guinea Grass was one of the earliest African Grasses to be introduced as a cattle forage. It thrives in wetter environments, growing best on well-drained soils where annual rainfall exceeds about 1,000 mm. In drier environments, it can colonise low lying areas and creeklines. It is commonly found in disturbed sites, and spreading along tracks and roads.

Guinea Grass forms dense clumps up to 1.5 m high. It can regenerate from seed, but generally persists through expansion of its perennial rootstock. It has been recorded in the Victoria River District, in the Daly and on the Sturt Plateau, and at scattered locations across the Arnhem Land coast. It occurs in isolated patches on the Tiwi Islands.

Impact

Guinea Grass is a prime example of conflicting interest between wildlife conservation and pastoral production. It not only dominates the understorey where conditions are suitable, but its productive biomass promotes intense fires that can kill canopy trees. Where the moist edges adjoining rainforests are invaded by guinea grass, fires are known to reduce the extent rainforest patches. This process could become a significant threat to Tiwi Rainforest taxa, notably Taracumbi Fern, Darwin Palm. and numerous rainforest trees, such as Blue Quandong and Native Walnut. Orchids that grow on tree branches will be particularly susceptible to hot fires fuelled by Guinea Grass. The Land Snail Trochomorpha melvillensis is also at risk, as where Guinea Grass has invaded its spring-fed rainforest habitat. Guinea Grass could also threaten species that use patches of bare ground for feeding sites, such as Partridge Pigeon and Butler's Dunnart.

Classification

Despite its impact, and a recommendation for weed listing in the Northern Territory Parks and Conservation Masterplan, Guinea Grass is not formally classed as a weed at the State/Territory or National Level. Advice provided by the Northern Territory government on the establishment of Buffel Grass pasture includes preventing its spread to roadsides or adjacent properties. It is listed as a high impact weed in the Field Guide to Assessing Australia’s Tropical Riparian Zones.

Control

There are various ways to control Guinea Grass. The most effective method is to dig up isolated clumps before the plants spread. Pesticides used for control of Guinea Grass include Glyphosate (Roundup®) and Fluazifop-p-butyl (Fusilade®). Pesticides should be used with care in and around wetland environments. Glyphosate is a non-specific weedicide, but is of low toxicity to wetlands animals. Fluazifop-p-butyl is a selective herbicide for grass control with a low toxicity to wetland animals, but needs to be used carefully around sedges, which it also kills.