Future Northland Pastures: 5. Potential sleeper weeds of pastoral systems in Northland, New Zealand

Abstract

We identified sleeper weeds: species that are already naturalised but remain limited in distribution and are likely capable of spreading into pastures in Northland, New Zealand. The species were significant agricultural weeds overseas, including subtropical species that could expand with climate change. We identified 33 potential sleeper weeds, comprising four grasses, twenty-two broadleaf herbs, one succulent herb, and six shrubs. The low forage quality grasses (Chloris gayana, Digitaria ciliaris, Melinis repens, Setaria sphacelata) are known to invade pastures. Six species toxic to livestock were identified. Three quarters of all the species are known problems in subtropical or tropical areas globally, so may be emerging problems under climate change. Regular incipient weed surveys and farmer reporting in both urban and agricultural areas are crucial, as these locations are often overlooked. Vigilance in detecting unusual plants, coupled with strict farm hygiene, remains the best strategy to prevent new weed spread.