Weed related yield losses ranging from 15 % to 56 % for silage and 15 % to 61 % for grain have been observed in New Zealand maize systems. And with herbicide resistance being an ongoing challenge growers need to know if and when to spray to maintain herbicide effectiveness and manage input costs. This update discusses the results of a three-year AgResearch-FAR, post-emergence herbicide trial to evaluate the effects of various herbicide treatments on different weed species at both small and large growth stages.
Herbicide resistance is an ongoing challenge. A 2021–2022 survey of maize crops in key growing regions of New Zealand’s North Island revealed herbicide resistance on 61 % of farms in Waikato, 31 % in Bay of Plenty, and 9 % in Hawke’s Bay. Resistant weeds identified included fathen (Chenopodium album), resistant to atrazine (Group 5), and summer grass (Digitaria sanguinalis), resistant to nicosulfuron (Group 2). AgResearch, in collaboration with FAR, conducted a three-year post-emergence herbicide trial to evaluate the effects of various herbicide treatments on different weed species at both small and large growth stages. The results, summarized in this update, provide valuable guidance on selecting the most effective herbicides for the specific weed species present in a crop.The Mode of Action (MoA) Group for each herbicide is included, enabling consideration of herbicides from different MoA Groups to support resistance management strategies.
Read Post-emergence herbicides for management of weeds in maize here