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Growing plantain (Plantago lanceolata) within pastures reduces nitrate leaching following grazing. Plantain is usually grown with grass and clover species, making selective weed control challenging. One strategy to selectively remove tall weeds in pastures with mixed species is to apply herbicides using weed wipers. However, for many months of the year, plantain has upright leafless flower stems that will intercept herbicide applied using wipers. To determine if this means plantain might be damaged by wipers used in such swards, two glasshouse experiments tested the tolerance of mature plantain plants to the application of herbicides suitable for use in weed wipers (glyphosate, clopyralid, aminopyralid, dicamba, metsulfuron, picloram and triclopyr) to the flower stems. Aminopyralid (0.075% ai solution) and a low rate of glyphosate (1.8% ai) caused the least decrease in plantain biomass and should be safe for weed wiping within swards containing plantain. A higher rate of glyphosate (7.2% ai) and a glyphosate/metsulfuron mix (0.9% + 0.01% ai, respectively) caused the most damage to plantain, particularly following simulated rainfall after application. Thus, applying some herbicides using wipers should be possible for selective weed control within plantain swards even if rain falls soon afterwards, though field trials are required to fine-tune recommendations. [ABSTRACT FROM AUTHOR]

BACKGROUND: Resistance to dicamba in Chenopodium album was first documented over a decade ago, however, the molecular basis of dicamba resistance in this species has not been elucidated. In this research, the resistance mechanism in a dicamba‐resistant C. album phenotype was investigated using a transcriptomics (RNA‐sequence) approach. RESULTS: The dose–response assay showed that the resistant (R) phenotype was nearly 25‐fold more resistant to dicamba than a susceptible (S) phenotype of C. album. Also, dicamba treatment significantly induced transcription of the known auxin‐responsive genes, Gretchen Hagen 3 (GH3), small auxin‐up RNAs (SAURs), and 1‐aminocyclopropane‐1‐carboxylate synthase (ACS) genes in the susceptible phenotype. Comparing the transcripts of auxin TIR/AFB receptors and auxin/indole‐3‐acetic acid (AUX/IAA) proteins identified from C. album transcriptomic analysis revealed that the R phenotype contained a novel mutation at the first codon of the GWPPV degron motif of IAA16, resulting in an amino acid substitution of glycine (G) with aspartic acid (D). Sequencing the IAA16 gene in other R and S individuals further confirmed that all the R individuals contained the mutation. CONCLUSION: In this research, we describe the dicamba resistance mechanism in the only case of dicamba‐resistant C. album reported to date. Prior work has shown that the dicamba resistance allele confers significant growth defects to the R phenotype investigated here, suggesting that dicamba‐resistant C. album carrying this novel mutation in the IAA16 gene may not persist at high frequencies upon removal of dicamba application. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Although New Zealand is developing an increasing number of herbicide-resistant weed populations, it has a much lower incidence of herbicide resistance than Australia. Understanding the reasons for these differences may help with future management of herbicide resistance in both countries. Australia is much larger than New Zealand so greater areas of weeds are exposed to herbicides annually in Australia. Another difference is the high frequency of Lolium rigidum in Australian agricultural systems, a species almost absent in New Zealand, and many of the cases of resistance in Australia involve this species. However, species closely related to L. rigidum are increasingly being found resistant to herbicides in New Zealand. Higher rainfall in most parts of New Zealand allows much more crop rotation than is possible in Australia, and greater crop yields give New Zealand farmers more flexibility to use higher application rates and more expensive herbicides in rotation than is feasible in Australia. Dry conditions result in more use of summer fallows in Australia using glyphosate which has caused some of the problems. Selection pressure for resistance still occurs in New Zealand, so herbicide and crop rotation may just be delaying the appearance of resistance in this country. [ABSTRACT FROM AUTHOR]

Resistance to iodosulfuron, a herbicide targeting acetolactate synthase (ALS), was identified and characterised in a population of Lolium perenne L. from Canterbury, New Zealand. The resistant population was 264 times more resistant to iodosulfuron than a susceptible population, based on a ratio of the rate corresponding to a 50% reduction in resistant and susceptible plant survival (R/S LD50). The resistant population was also 14-times more resistant to nicosulfuron, another ALS-inhibitor of the same class. However, no resistance to imazapyr, an ALS-inhibitor from a different chemical class, was detected in the resistant population. Pre-treatment with an inhibitor of cytochrome P450 reduced the level of iodosulfuron resistance to 46-fold in the resistant population, suggesting enhanced herbicide metabolism, a non-target site mechanism, contributed to resistance of this herbicide. In addition, a proline to leucine substitution at codon 197 was detected, suggesting a target-site-based mechanism was also associated with resistance to iodosulfuron. This is the first report on the resistance mechanisms to ALS-inhibiting herbicides identified in Lolium perenne in New Zealand and highlights the importance of integrated weed management approaches to reduce the likelihood of ALS-inhibitor herbicide resistance becoming more widespread. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Acetyl-coenzyme A carboxylase (ACCase) inhibitors such as haloxyfop, pinoxaden and clethodim selectively control grass weed species in many types of crop. Here, we characterised two populations of Lolium multiflorum (Italian ryegrass), R and RV, from South Canterbury and Central Otago respectively, that were suspected to be resistant to ACCase-inhibiting herbicides. Based on 50% reduction in biomass (GR50), in two dose–response experiments, both populations were highly resistant to haloxyfop with resistance factors (RF) >400 times, but resistance to pinoxaden was low (RF of 2). Furthermore, population R was found to be moderately resistant to clethodim (RF >4, based on 50% reduction in survival (LD50)), but population RV had RFs barely greater than 1, based on GR50. Gene sequencing showed that the same target site mutation (Ile-2041-Asn) was associated with resistance to the three herbicides in both populations. The zygosity of the resistance alleles in the plants tested could cause the differences in resistance to clethodim observed between the populations, even though they carried the same mutation. This is the first report of the mechanism of resistance to ACCase-inhibiting herbicides in Italian ryegrass from New Zealand. [ABSTRACT FROM AUTHOR]

Organic soil amendments can be useful for improving degraded soil, but this increase in organic matter (OM) may influence adsorption of herbicides subsequently applied to the treated soil, even though the particle size of amendments and their nature differ from typical soil OM. In this study, a batch equilibrium method was used to measure adsorption of five herbicides following application to two organic media, wood pulp and sawdust, comparing these with two cropping soils. Herbicide adsorption, quantified by distribution coefficients (kd), was much higher in the two organic media than in the cropping soils. The increases in adsorption were strongly correlated to the percentage of organic carbon. When the kd was normalized to adsorption coefficients corrected for OM content (koc), variation in results between the media was greatly reduced, indicating that OM is an important factor influencing adsorption in these media. The results of this study suggest that herbicides will be less effective when applied to soils in which sawdust and wood pulp have been added. Using organic amendments to remediate soil will increase adsorption of pesticides, reducing their bio-availability and efficacy, but also reducing their tendency to leach into root zones of deep-rooted crops and into groundwater. [ABSTRACT FROM AUTHOR]

The mode of inheritance for herbicide resistance was investigated in a population of Lolium multiflorum (Italian ryegrass) with restricted glyphosate translocation mechanism of resistance. The degree of dominance for glyphosate resistance in Italian ryegrass was evaluated in the progenies of F1 families which were created by reciprocal-crossing between resistant (R) and susceptible (S) parental individuals. The results showed an intermediate level of glyphosate resistance for F1 families compared to that of the parental types. The phenotypic resistance segregation was also investigated using backcross families which were created by pair-crossing the F1 individuals to the susceptible population, and the observed segregation values fitted a one-gene model very well. Thus it appears that glyphosate resistance in the Italian ryegrass obtained from a New Zealand vineyard with restricted herbicide translocation is controlled by a single incompletely dominant nuclear gene. [ABSTRACT FROM AUTHOR]

This study examined if glyphosate-resistant populations of Lolium multiflorum and Lolium perenne from some New Zealand vineyards were still susceptible to glufosinate and amitrole. The response of plants of one glyphosate-resistant population of L. multiflorum , population A, and two glyphosate-resistant L. perenne populations, populations J and O, to glufosinate and amitrole were evaluated and compared to susceptible populations in two dose–response experiments. Based on the herbicide rates giving 50% reduction in growth (GR 50 values), populations A, J and O were 3.9, 4.5 and 3.8 times more resistant to glufosinate respectively, compared to the susceptible populations in a glufosinate dose–response experiment. Populations A, J and O were also found to be 2.9, 5.0 and 13.1 times more resistant to amitrole respectively, in an amitrole dose–response experiment. Very similar results were obtained when both dose–response experiments were repeated. This is the first confirmed report of weed species that have developed multiple-resistance to glyphosate, glufosinate and amitrole. These are the three main herbicides currently used for weed control in New Zealand vineyards. [ABSTRACT FROM AUTHOR]