A century of weed change in New Zealand’s forage seed multiplication industry

International seed trading provides a significant introductory pathway for weed seeds, and many globally established weeds originated as contaminants in agricultural lots. Management of these trade systems helps minimize losses is an important means preventing future biological incursions. Forage crop lots could be considered higher risk than arable vegetable crops, they have been found to percentage contaminated Two the most commonly used temperate forage crops worldwide are perennial ryegrass ( Lolium perenne ) white clover Trifolium repens ). New Zealand one top producers seeds globally, both species pastures. Using historical current lot analytical purity test results, we examined frequency, identity temporal changes within grown from 1912 2019. Overall, decreased between approximately three sixfold over study period, indicating that herbicide availability, certification improved management effective control. However, identified handful annual become more problematic future, either because showed increasing presence trend or were common contaminants. In 2019, Vulpia bromoides was contaminant lots, Chenopodium album Sherardia arvensis Poa annua , with trend, had largest increases period. Conversely, Rumex acetosella decline species. There difference grass where four times clover. Considering trades half world’s countries contributes substantially global supply seed, our unique insight into spectrum throughout sowing system last century.