Prickly solanum/pico (Solanum torvum)
This invasive plant thrives in disturbed environments and can be highly problematic in pastures, roadsides, and wastelands and poisonous to livestock. It can impede passage for humans and animals as its leaves and stems contain sharp spines. The plant’s abundant seed production and dispersal by fruit-eating birds make it difficult to manage.
Pasture in Vanuatu infested with prickly solanum/pico
Impacts
Pico’s rapid growth and competitive nature allow it to quickly outcompete other vegetation, especially after disturbance events like slashing or land clearing. It overtops most herbs, grasses, and shrubs, limiting other species. Pico presents a major challenge, particularly in pasturelands where due to its unpalatability it is avoided by livestock, and forms dense thickets, shading out of desirable forage species
Prickly solanum/pico in the Pacific
In Vanuatu, where cattle farming is a significant livelihood, the spread of pico has resulted in a documented decline in cattle numbers.
Farmers report that 91% of farms in Vanuatu are affected by weeds with an estimated 34% of pasture lost to weeds. On many farms, pico ranks as the most important or second most problematic weed. The resulting reduction in pasture quality has forced some farmers to scale down or abandon cattle farming altogether.
Beyond its impact on agriculture, pico fruits can serve as a host for some fruit flies present in other parts of the Pacific, which are serious pests of fruit and vegetable crops. This creates additional economic pressures for farmers growing commercial crops. Although the fruits of pico are sometimes used in cooking in some parts of the world, there are reports of poisoning from eating them. The amount of toxins in the fruit varies greatly, perhaps due to genetics and levels of environmental stress affecting the plants. We are unaware of pico fruits being eaten in the Pacific.
Control Methods
Mechanical methods of control (e.g., cutting or pulling the plants) are not as effective or practical as chemical methods. In Vanuatu, slashing may be applied to control dense thickets, prior to follow up control options, such as herbicide. Although these methods are all labour intensive and impractical for large infestations.
A new approach involving natural enemies now offers some hope for controlling pico. A specialist beetle (Leptinotarsa undecimlineata) from Jamaica was introduced to Vanuatu in 2024. This beetle can significantly damage its host plant and is expected to reduce the invasiveness of pico.
Key contacts
