Seedbank persistence of four summer grass weed species in the northeast cropping region of Australia

Summer grass weed species are a particular problem in the northeast cropping region of Australia because they are prolific seeders and favor no-till systems. Information on weed seed persistence levels can be used for the development of effective and sustainable integrated weed management programs. A field study was conducted over 42 months to evaluate the seedbank persistence of Chloris truncata, C. virgata, Dactyloctenium radulans, and Urochloa panicoides as affected by burial depth (0, 2, and 10 cm). Regardless of species, buried seeds persisted longer than surface seeds and there was no difference in seed persistence between 2 and 10 cm depths. Surface seeds of C. truncata depleted completely in 12 months and buried seeds in 24 months. Similarly, C. virgata seeds placed on the soil surface depleted in 12 months. Buried seeds of this species took 18 months to completely deplete, suggesting that C. truncata seeds persist longer than C. virgata seeds. Surface seeds of D. radulans took 36 months to completely deplete, whereas about 7% of buried seeds were still viable at 42 months. U. panicoides took 24 and 42 months to completely exhaust the surface and buried seeds, respectively. These results suggest that leaving seeds on the soil surface will result in a more rapid depletion of the seedbank. Information on seed persistence will help to manage these weeds using strategic tillage operations.

Monoclonal Antibody-Based Immunosensor for the Electrochemical Detection of Chlortoluron Herbicide in Groundwaters

Chlortoluron (3-(3-chloro-p-tolyl)-1,1-dimethyl urea) is an herbicide widely used in substitution to isoproturon to control grass weed in wheat and barley crops. Chlortoluron has been detected in groundwaters for more than 20 years; and dramatic increases in concentrations are observed after intense rain outbreaks. In this context; we developed an immunosensor for the determination of chlortoluron based on competitive binding of specific monoclonal antibodies on chlortoluron and immobilized biotinylated chlortoluron; followed by electrochemical detection on screen-printed carbon electrodes. The optimized immunosensor exhibited a logarithmic response in the range 0.01–10 µg·L−1; with a calculated detection limit (LOD) of 22.4 ng·L−1; which is below the maximum levels allowed by the legislation (0.1 µg·L−1). The immunosensor was used for the determination of chlortoluron in natural groundwaters, showing the absence of matrix effects.

Transfer of resistance alleles from herbicide-resistant to susceptible grass weeds via pollen-mediated gene flow

The objective of this paper was to review the reproductive biology, herbicide-resistant (HR) biotypes, pollen-mediated gene flow (PMGF), and potential for transfer of alleles from HR to susceptible grass weeds including barnyardgrass, creeping bentgrass, Italian ryegrass, johnsongrass, rigid (annual) ryegrass, and wild oats. The widespread occurrence of HR grass weeds is at least partly due to PMGF, particularly in obligate outcrossing species such as rigid ryegrass. Creeping bentgrass, a wind-pollinated turfgrass species, can efficiently disseminate herbicide resistance alleles via PMGF and movement of seeds and stolons. The genus Agrostis contains about 200 species, many of which are sexually compatible and produce naturally occurring hybrids as well as producing hybrids with species in the genus Polypogon. The self-incompatibility, extremely high outcrossing rate, and wind pollination in Italian ryegrass clearly point to PMGF as a major mechanism by which herbicide resistance alleles can spread across agricultural landscapes, resulting in abundant genetic variation within populations and low genetic differentiation among populations. Italian ryegrass can readily hybridize with perennial ryegrass and rigid ryegrass due to their similarity in chromosome numbers (2n=14), resulting in interspecific gene exchange. Johnsongrass, barnyardgrass, and wild oats are self-pollinated species, so the potential for PMGF is relatively low and limited to short distances; however, seeds can easily shatter upon maturity before crop harvest, leading to wider dispersal. The occurrence of PMGF in reviewed grass weed species, even at a low rate is greater than that of spontaneous mutations conferring herbicide resistance in weeds and thus can contribute to the spread of herbicide resistance alleles. This review indicates that the transfer of herbicide resistance alleles occurs under field conditions at varying levels depending on the grass weed species.

The Coaxium® Wheat Production System: A New Herbicide-Resistant System for Annual Grass Weed Control and Integrated Weed Management

The authors discuss the importance of wheat as a global food source and describe a novel multi-institutional, public-private partnership between Colorado State University, the Colorado Wheat Research Foundation, and private chemical and seed companies that resulted in the development of a new herbicide-resistant wheat production system.

Low Effectiveness of Prosulfocarb and Mesosulfuron-Methyl + Iodosulfuron-Methyl against Vulpia Myuros

Due to natural tolerance to most widely used herbicides for grass weed control, prosulfocarb as pre-emergence or early post-emergence herbicide and mesosulfuron + iodosulfuron as post-emergence herbicide are the mainstays of any chemical control program for Vulpia myuros in Denmark. However, farmers often report variable efficacy of these herbicides on V. myuros compared to other grass weeds. Dose–response experiments were conducted to evaluate the performance of prosulfocarb and mesosulfuron + iodosulfuron on V. myuros. Prosulfocarb was sprayed at different plant growth stages to study the influence of plant growth stage on the performance of prosulfocarb on V. myuros in comparison with the more susceptible grass weed species Apera spica-venti. Doses causing 50% reduction in response variable (ED50) were estimated from the dose–response analysis. The ED50 values revealed a higher tolerance of V. myuros to prosulfocarb and mesosulfuron + iodosulfuron than A. spica-venti. The relative difference in the effectiveness of prosulfocarb between V. myuros and A. spica-venti was constant among plant growth stages studied. The highest levels of V. myuros control were achieved when prosulfocarb was sprayed pre-emergence (BBCH 00), while the control substantially declined at later growth stages. The results from the current study document the tolerance of V. myuros to prosulfocarb and mesosulfuron + iodosulfuron and highlight the importance of optimization of prosulfocarb spray timing for achieving maximum control of V. myuros.

Early Detection of Broad-Leaved and Grass Weeds in Wide Row Crops Using Artificial Neural Networks and UAV Imagery

Significant advances in weed mapping from unmanned aerial platforms have been achieved in recent years. The detection of weed location has made possible the generation of site specific weed treatments to reduce the use of herbicides according to weed cover maps. However, the characterization of weed infestations should not be limited to the location of weed stands, but should also be able to distinguish the types of weeds to allow the best possible choice of herbicide treatment to be applied. A first step in this direction should be the discrimination between broad-leaved (dicotyledonous) and grass (monocotyledonous) weeds. Considering the advances in weed detection based on images acquired by unmanned aerial vehicles, and the ability of neural networks to solve hard classification problems in remote sensing, these technologies have been merged in this study with the aim of exploring their potential for broadleaf and grass weed detection in wide-row herbaceous crops such as sunflower and cotton. Overall accuracies of around 80% were obtained in both crops, with user accuracy for broad-leaved and grass weeds around 75% and 65%, respectively. These results confirm the potential of the presented combination of technologies for improving the characterization of different weed infestations, which would allow the generation of timely and adequate herbicide treatment maps according to groups of weeds.

Distribution, Genetic Diversity and Population Structure of Aegilops tauschii Coss. in Major Wheat-Growing Regions in China

Aegilops tauschii Coss. is known as a noxious grass weed seriously affecting wheat quality and yield. To investigate its present occurrence in wheat fields and the potential genetic diversity of the grass weed in China, a filed survey covering major wheat production regions was conducted during 2017–2019. Seeds of different Ae. tauschii populations collected from the survey were analyzed with Simple Sequence Repeats (SSRs) technique. Results showed that Ae. tauschii was occurring in each of the provinces surveyed with varied occurrence frequency ranging from 0.91% in Sichuan Province to 92.85% in Henan Provinces. Eighty alleles with size ranging from 98 bp to 277 bp were detected from the 192 collected Ae. tauschii populations with 17 SSR markers. Ae. tauschii, in this study, exhibited a moderately high level of genetic diversity, high differentiation, deficient heterozygosity and limited gene flow. Compared with other provinces, Hubei populations possessed relatively low genetic diversity. Dendrogram analysis showed that genetic distance did not seem to be related to geographic distribution. Additionally, STRUCTURE analysis suggested that Ae. tauschii populations in wheat fields of China can be divided into three groups, which was further supported by cluster analysis. Among the three groups, solely 7% of the total variation was detected, whereas the majority variation (67%) occurred among different populations within same group. Undoubtedly, such information will help us to better understand population relationships and spread of Ae. tauschii in China and will provide a new perspective for its integrated management.

Gamma-rays in the development of rice lines tolerant to aryloxyphenoxypropionate herbicides.

The aryloxyphenoxypropionate (APP) herbicides are graminicides with excellent control of many grass weed species, including weedy rice (Oryza sativa L.). These herbicides block fatty acid biosynthesis by inhibition of the enzyme acetyl-CoA carboxylase (ACCase) and cause death of the plant. Through induced mutation of rice seeds with gamma-rays, rice lines resistant to APP have been developed. Plant dose-response assays confirmed resistance to the APP herbicides quizalofop-p-ethyl and haloxyfop-p-methyl. The carboxyl-transferase (CT) domain fragments of ACCase from the resistant line and the susceptible control were sequenced and compared. A point mutation was detected in the amino acid position 2027. Results indicated that resistance to APP herbicides is a consequence of an altered ACCase enzyme that confers resistance. APP-resistant rice provides an option to improve the efficiency of weed management in rice crops.