Assessing the Capability and Potential of LiDAR for Weed Detection.

Conventional methods of uniformly spraying fields to combat weeds, requires large herbicide inputs at significant cost with impacts on the environment. More focused weed control methods such as site-specific weed management (SSWM) have become popular but require methods to identify weed locations. Advances in technology allows the potential for automated methods such as drone, but also ground-based sensors for detecting and mapping weeds. In this study, the capability of Light Detection and Ranging (LiDAR) sensors were assessed to detect and locate weeds. For this purpose, two trials were performed using artificial targets (representing weeds) at different heights and diameter to understand the detection limits of a LiDAR. The results showed the detectability of the target at different scanning distances from the LiDAR was directly influenced by the size of the target and its orientation toward the LiDAR. A third trial was performed in a wheat plot where the LiDAR was used to scan different weed species at various heights above the crop canopy, to verify the capacity of the stationary LiDAR to detect weeds in a field situation. The results showed that 100% of weeds in the wheat plot were detected by the LiDAR, based on their height differences with the crop canopy.

Identification of the first glyphosate-resistant capeweed (Arctotheca calendula) population.

BACKGROUND: Glyphosate is routinely used in Australia to control the Arctotheca species Arctotheca calendula (L.) Levyns (referred hereinafter as capeweed). This study identifies the first global case of field-evolved glyphosate-resistant capeweed, collected from the grainbelt of Western Australia. RESULTS: In 2020, a capeweed biotype that was collected from Borden in the southern Western Australian grainbelt was confirmed to be glyphosate-resistant (referred hereinafter as Spence population). When compared to the pooled mortality of six field-collected, glyphosate susceptible capeweed populations (S1, S2, S3, S4, S5 and S6), the Spence population was found > 11-fold more resistant to glyphosate than the pooled results of the susceptible populations (S1-S6) at the lethal dose of 50% (LD50 ) level. The growth of the Spence population was also less affected, requiring > 13-fold more glyphosate to reduce growth than the pooled susceptible populations at the growth reduction of 50% (GR50 ) level. Sequencing of the plastidic 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene indicated no known single gene mutation imparting glyphosate resistance. This study, however, did not investigate any other known mechanisms that impart glyphosate resistance. When screened at the field-applied rate, this Spence population was also found to survive an inhibitor of acetolactate synthase (ALS) (metosulam) and an inhibitor of phytoene desaturase (diflufenican). CONCLUSIONS: This is the first confirmation of glyphosate resistance evolution in a capeweed population globally. With capeweed resistance already confirmed to photosystem-I inhibiting herbicides (paraquat and diquat), this study emphasizes the importance of using integrated measures that do not depend only on the use of non-selective herbicides for controlling herbicide resistance-prone capeweed populations. © 2021 Society of Chemical Industry.

Farming without Glyphosate?

Recent statements from scientific organisations and court decisions have resulted in widespread public interest and concern over the safety of glyphosate, the most popular and effective herbicide used worldwide. Consequently, glyphosate-based products are under intense scrutiny from governments at all levels. Some jurisdictions have already banned or restricted its use, which will adversely impact international trade in bulk grain commmodities if glyphosate residues are detected. The possibility of farming without glyphosate is becoming an important issue facing the agri-food research and development sector. Contingency plans need to be formulated if that scenario becomes a reality. In this review, we briefly summarize international events that have led to this possible situation, describe current glyphosate usage in major agronomic field crops worldwide, outline possible alternatives to glyphosate in two agroregions and perform bioeconomic model scenarios of southern Australian broadacre cropping systems without the herbicide. Model predictions suggest that we can farm profitably without glyphosate by consistently utilizing key non-herbicidal weed management practices combined with robust pre-emergence soil residual herbicide treatments. However, maintaining low weed seed banks will be challenging. If the social license to use glyphosate is revoked, what other pesticides will soon follow?

Herbicide Resistance Management: Recent Developments and Trends.

This review covers recent developments and trends in herbicide-resistant (HR) weed management in agronomic field crops. In countries where input-intensive agriculture is practiced, these developments and trends over the past decade include renewed efforts by the agrichemical industry in herbicide discovery, cultivation of crops with combined (stacked) HR traits, increasing reliance on preemergence vs. postemergence herbicides, breeding for weed-competitive crop cultivars, expansion of harvest weed seed control practices, and advances in site-specific or precision weed management. The unifying framework or strategy underlying these developments and trends is mitigation of viable weed seeds into the soil seed bank and maintaining low weed seed banks to minimize population proliferation, evolution of resistance to additional herbicidal sites of action, and spread. A key question going forward is: how much weed control is enough to consistently achieve the goal of low weed seed banks? The vision for future HR weed management programs must be sustained crop production and profitability with reduced herbicide (particularly glyphosate) dependency.

Narrow windrow burning canola (Brassica napus L.) residue for Sclerotinia sclerotiorum (Lib.) de Bary sclerotia destruction.

BACKGROUND: Since the introduction of herbicide-tolerant varieties of canola (Brassica napus L.) in 1993, global plantings have increased resulting in an increased incidence of Sclerotinia sclerotiorum (Lib.) de Bary infections. Developments in narrow windrow burning techniques to destroy the seed of multiple herbicide-resistant weeds provide an opportunity to also intercept and heat-treat the S. sclerotiorum inoculum source, termed sclerotia, before it re-enters the soil to infect susceptible crop species in successive years. RESULTS: Preliminary kiln studies determined that a temperature of 264 °C for 10 s was needed to destroy S. sclerotiorum sclerotia viability (LT99 ) of sclerotia < 3 mm in diameter, whereas temperatures of 353 and 362 °C for the same duration were required to kill sclerotia (LT99 ) of 3-4 and > 4 mm in diameter respectively. In the field, temperatures > 500 °C were maintained in the centre of burning narrow windrows of canola residue for > 450 s and 300 °C was maintained consistently at either edge of the windrows for the same duration. The temperatures achieved when burning canola narrow windrows were sufficient to kill all sclerotia concentrated into the narrow windrow. CONCLUSION: As a technique, narrow windrow burning of canola residue provides the temperature and temperature durations required to kill S. sclerotiorum sclerotia, thus providing a non-fungicidal control option as part of a wider integrated disease management approach. © 2018 Society of Chemical Industry.

Recurrent selection with reduced 2,4-D amine doses results in the rapid evolution of 2,4-D herbicide resistance in wild radish (Raphanus raphanistrum L.).

BACKGROUND: When used at effective doses, weed resistance to auxinic herbicides has been slow to evolve when compared with other modes of action. Here we report the evolutionary response of a herbicide-susceptible population of wild radish (Raphanus raphanistrum L.) and confirm that sublethal doses of 2,4-dichlorophenoxyacetic acid (2,4-D) amine can lead to the rapid evolution of 2,4-D resistance and cross-resistance to acetolactate synthase (ALS)-inhibiting herbicides. RESULTS: Following four generations of 2,4-D selection, the progeny of a herbicide-susceptible wild radish population evolved 2,4-D resistance, increasing the LD50 from 16 to 138 g ha-1 . Along with 2,4-D resistance, cross-resistance to the ALS-inhibiting herbicides metosulam (4.0-fold) and chlorsulfuron (4.5-fold) was evident. Pretreatment of the 2,4-D-selected population with the cytochrome P450 inhibitor malathion restored chlorsulfuron to full efficacy, indicating that cross-resistance to chlorsulfuron was likely due to P450-catalysed enhanced rates of herbicide metabolism. CONCLUSION: This study is the first to confirm the rapid evolution of auxinic herbicide resistance through the use of low doses of 2,4-D and serves as a reminder that 2,4-D must always be used at highly effective doses. With the introduction of transgenic auxinic-herbicide-resistant crops in the Americas, there will be a marked increase in auxinic herbicide use and therefore the risk of resistance evolution. Auxinic herbicides should be used only at effective doses and with diversity if resistance is to remain a minimal issue. © 2016 Society of Chemical Industry.

Directional selection for flowering time leads to adaptive evolution in Raphanus raphanistrum (Wild radish).

Herbicides have been the primary tool for controlling large populations of yield depleting weeds from agro-ecosystems, resulting in the evolution of widespread herbicide resistance. In response, nonherbicidal techniques have been developed which intercept weed seeds at harvest before they enter the soil seed bank. However, the efficiency of these techniques allows an intense selection for any trait that enables weeds to evade collection, with early-flowering ecotypes considered likely to result in early seed shedding. Using a field-collected wild radish population, five recurrent generations were selected for early maturity and three generations for late maturity. Phenology associated with flowering time and growth traits were measured. Our results demonstrate the adaptive capacity of wild radish to halve its time to flowering following five generations of early-flowering selection. Early-maturing phenotypes had reduced height and biomass at maturity, leading to less competitive, more prostrate growth forms. Following three generations of late-flowering selection, wild radish doubled its time to flowering time leading to increased biomass and flowering height at maturity. This study demonstrates the potential for the rapid evolution in growth traits in response to highly effective seed collection techniques that imposed a selection on weed populations within agro-ecosystems at harvest.

Identification of the first glyphosate-resistant wild radish (Raphanus raphanistrum L.) populations.

BACKGROUND: In Australia, glyphosate has been used routinely to control wild radish (Raphanus raphanistrum L.) for the past 40 years. This study focuses on two field-evolved glyphosate-resistant populations of wild radish collected from the grainbelt of Western Australia. RESULTS: Two wild radish biotypes were confirmed to be glyphosate resistant by comparing R/S of two suspected populations. Based on R/S from dose-response curves, the R1 and R2 populations were 2.3 and 3.2 times more resistant to glyphosate respectively. Dose response on glyphosate-selected progeny (>1080 g ha(-1)) demonstrated that the glyphosate resistance mechanism was heritable. When compared with the pooled mortality results of three known susceptible populations (S1, S2 and S3), the R1 and R2 subpopulations were 3.4-fold and 4.5-fold more resistant at the LD50 level respectively. Both populations were found to have multiple resistance to the phytoene desaturase inhibitor; diflufenican, the synthetic auxin; 2,4-D and the ALS inhibitors; chlorsulfuron, sulfometuron-methyl, imazethapyr and metosulam. CONCLUSIONS: This is the first report confirming glyphosate resistance evolution in wild radish and serves to re-emphasise the importance of diverse weed control strategies. Proactive and integrated measures for resistance management need to be developed to diversify control measures away from glyphosate and advance the use of non-herbicidal techniques.