Maize and sweetcorn growers in New Zealand can blunt fall armyworm by planting as early as is practical, according to new research from the Foundation for Arable Research (FAR). Over the past three seasons the crops most damaged by the pest were generally those sown late — particularly in late November and December, FAR biosecurity officer Ash Mills said.

In Northland, late planting has coincided with second-generation armyworm flights and larger populations, bringing more plant damage, more insecticide and lower yields. Later-planted crops in other regions have also seen higher pest pressure and cob damage. Planting time, crop growth stage and regular scouting are the themes of FAR's just-released report, Fall armyworm population trends in New Zealand 2022–2026.

The report's author, Dr Scott Hardwick of the Bioeconomy Science Institute, said populations have been tracked by pheromone trapping and crop scouting since the moth was first detected in 2022. Fall armyworm is now present year-round in the northern third of the North Island and, in warm years, may persist through winter in coastal parts of the southern North Island and the northern South Island.

The pest runs up to four generations a year in northern New Zealand and one or two further south, in places such as Golden Bay, Canterbury and the West Coast. Trap catches have risen every season since 2022, especially in Northland, even as the trapping grid has shrunk — a pattern Hardwick says is expected of a species still in its invasive phase and yet to reach equilibrium.

Serious damage happens when moths are flying while the crop is at a vulnerable early growth stage: from November onwards in the Far North and between December and March further south. Once a population establishes in a crop it tends to build through the season. Maize silage crops appear relatively unaffected if early damage is limited, but cob damage in maize grain and sweetcorn can be extensive and costly, so those crops should be scouted regularly through the whole cycle.

Source: Farmers Weekly NZ