Evolution of resistance in weeds to herbicides is threatening world agricultural production. Weed management has become more complicated with the development of non-target site resistance (NTSR) to herbicides in weeds. The NTSR mechanisms can be caused by herbicide metabolism, altered patterns of translocation, and herbicide absorption/penetration. Metabolism of herbicides consists of an activation phase and then a conjugation phase, though in some cases no activation phase is needed. The activation phase mainly involves the addition of functional groups to herbicide molecules using enzymes such as cytochrome P-450. Transcriptome-wide gene expression has shown that genes which encode for several cytochrome P-450s are upregulated in weeds resistant to ACCase-inhibitor and ALS-inhibitor herbicides. In the conjugated phase, several studies have shown that two important types of enzyme, glutathione S-transferases and glucosyltransferases, play crucial roles in conferring resistance to herbicides. An altered pattern of translocation can also play a crucial role in conferring NTSR to weeds. With glyphosate and paraquat, it has been shown that altered patterns of translocation are due to sequestration of the herbicide into vacuoles. However, some other little known mechanisms such as “hyper-sensitive” reactions, impaired translocation, and root exudation can affect the patterns of herbicide translocation within resistant weeds. The molecular understanding of NTSR mechanisms is still in its infancy. Recent developments in techniques such as high-throughput DNA/RNA sequencing technologies will soon allow further insights into the NTSR mechanisms in weeds. This information is essential for developing strategies to overcome weeds with the NTSR mechanisms.

In New Zealand, pastoral farming for dairy and meat production is the major land use. As with any agricultural production system, weeds are a threat to efficient pasture production in New Zealand. In this review, we outline the problems caused by weeds in New Zealand pastures, and the management strategies being used to control them. There are currently 245 plant species from 40 plant families that are considered to be troublesome weeds in New Zealand pastures. The application of herbicides is an important approach to manage weeds in New Zealand pastures; however, a key to the success of these pastures is the use of clovers in combination with the grasses, so the challenge is to find herbicides that selectively control weeds without damaging these legumes. The use of spot spraying and weed wiping are often required to ensure selective control of some weed species in these pastures. Non-chemical agronomic approaches such as grazing management and using competitive pasture species often play a more important role than herbicides for weed management in many New Zealand pastures. Thus, integrated weed management using a combination of herbicides and good pasture management strategies leads to the most cost-effective and efficient control of pasture weeds in New Zealand.

For decades, herbicides have provided easy‐to‐use, cost‐effective weed management, but alternatives are desired. Consumer preference for chemical‐free food, awareness of environmental impacts, regulation increasingly restricting agrichemical use, and increasing prevalence of herbicide resistance are forcing changes to weed management strategies. New Zealand farming must remain sustainable and profitable while responding to changes in its overseas markets, among which are increasing demands for regeneratively grown, safe, high‐quality produce. Current reliance on herbicides should be reduced, with more emphasis on preventative management by cultural means, and weed suppression by alternative technologies. The emergence of agritechnologies incorporating automation, machine vision and artificial intelligence, and development of new techniques for weed destruction, offer alternatives that minimise or avoid the requirement for herbicides, avoid soil disturbance and can work effectively in high crop or crop‐residue conditions. We have identified electric weeding as a feasible alternative and pulsed electric microshocks as a very low‐energy option requiring a fraction of the energy of any other system. Pulsed microshocks enable an integrated weed management system for vegetable and arable crop production combining cultural controls and inexpensive pre‐planting treatments with automated application of chemical‐free in‐crop weed control. Open‐source software enables community development of autonomous deployment for niche crops.

The number of herbicide-resistant weeds is increasing globally. A successful management practice requires an understanding of how resistance traits are inherited. Weed scientists worldwide have investigated the mode of inheritance for herbicide resistance in weeds. Depending on the resistance gene/mechanism, varied patterns of inheritance have been documented in weed species. In most of the target-enzyme mechanism cases, the mode of inheritance involves a single nuclear gene. However, maternal (cytoplasmic) inheritance has also been documented for triazine-resistant weeds with the target-enzyme mutation mechanism of resistance. Resistance from target-enzyme overexpression is not always associated with the single-gene model of inheritance. Depending on the type of resistance, allelic dominance varies between complete dominance, semi-dominance and recessive for both target-enzyme mutation and target-enzyme overexpression mechanisms. The nontarget site mechanism of resistance is however, more complex. The pattern of inheritance in weeds with nontarget site resistance is quite variable and should be investigated case by case. The pattern of inheritance has a crucial role in the dynamics of herbicide-resistance within a weed population, and knowledge about the inheritance of herbicide resistance traits could help develop predictive models and novel strategies to prevent the spread of resistance allele(s).

Herbicide‐resistant weeds are serious threats to agricultural production. Since a review published in 1996, the number of different examples of weed biotypes developing resistance to one or more herbicides in New Zealand has almost quadrupled. By 1996, six weed species had been shown to have developed resistant biotypes, mostly to either triazine or auxinic herbicides. Most of the herbicide‐resistant weed species reported in 1996 were found in the pasture and arable sectors. Evolved herbicide resistance has now been confirmed for a further eight weed species, with resistance to nine herbicide sites of action (giving a total of 25 cases of resistance) now reported in different New Zealand agricultural and non‐agricultural sectors. Developing an effective herbicide resistance management strategy requires a good understanding of both the extent of the problem, and also molecular and biochemical aspects of herbicide resistance, in order to develop innovative techniques to overcome herbicide resistance.