Weed Decision Threshold as a Key Factor for Herbicide Reductions in Site-Specific Weed Management

Long-term studies are crucial for evaluating how intercropping affects the agronomic, environmental, and socio-economic sustainability of sugarcane systems. Intercropping with cover crops is expected to improve soil fertility and reduce herbicide use; however, its long-term effects on yield, weed dynamics, and production costs remain unclear, particularly under tropical conditions. Weed pressure has been hypothesized to drive yield decline over time, yet the temporal evolution of weed communities and their consequences for system sustainability remain poorly understood. We hypothesized that intercropping would modify ecosystem functions and services by increasing weed diversity and soil fertility, reducing herbicide use, and also increasing labor and production costs. To test this hypothesis, we conducted the first 7-year field experiment on Reunion Island, comparing four sugarcane intercropping systems with conventional chemical and low weed control systems. A multi-criteria approach assessed weed community dynamics, soil fertility, sugarcane yield and quality, herbicide use, labor, and economic performance over a complete crop cycle, including multiple ratoons. We show that weed pressure increased over time in both chemical and intercropping systems due to greater weed cover and species richness. Weed community structure differed during the first 3 years but later homogenized under sugarcane dominance. This increase led to more manual weeding in intercropping systems and to increased herbicide use in chemical ones, resulting in a 61% reduction in herbicide use under intercropping. After 7 years, soil chemical and biological fertility remained unchanged, while physical fertility improved with companion crop and weed development. Sugarcane yield and sucrose content were maintained, but production costs and working hours increased. This study demonstrates that sugarcane intercropping reduces herbicide dependence without compromising yield, though at higher labor costs. Systems maintaining spontaneous flora in inter-rows appear to offer a promising compromise for sustainable weed management. Further research on this system should be conducted in different pedoclimatic conditions.

Purpose This study explores the efficacy of microwaves as a method for the control of three weed species particularly widespread and problematic in the Italian farms cultivating IV range crops. These findings, based on laboratory experiments, are part of a project (MOPAS Project—Microwaves for Sustainable Agriculture) meant to realize a prototype for use in real field situations. Methods Seeds from weed species ( Trifolium repens L., Portulaca oleracea L., and Solanum nigrum L.) were subjected to microwave treatments at 480 and 900 W power levels for 10 and 30 s. The impact on seed germination and ion leakage was assessed. Histological changes induced by microwaves were also examined through microscopic analysis. Results Significant germinability decreases were observed in S. nigrum and T. repens with increasing treatment duration and intensity. P. oleracea exhibited lower sensitivity, with detrimental effects only at the highest power levels suggesting that seed size and the associated differences in water absorption may play a crucial role in determining sensitivity to microwave exposure. S. nigrum membrane stability was affected only at the highest irradiation power, while all species showed increased ion leakage across treatments. Observations revealed wilting of stems and leaves, indicating cell turgidity loss in inner tissue layers. Conclusion Microwave radiation may be a non-chemical weed control strategy, though efficacy is influenced by variability in seed traits. Further research is necessary to optimize treatment parameters and assess scalability under field conditions. This approach holds potential for reducing herbicide use and promoting sustainable agricultural practices.

Amongst the biodiversity components of agriculture, weeds are an interesting model for exploring management options relying on the principle of ecological intensification in arable farming. Weeds can cause severe crop yield losses, contribute to farmland functional biodiversity and are strongly associated with the generic issue of pesticide use. In this paper, we address the impacts of herbicide reduction following a causal framework starting with herbicide reduction and triggering changes in (i) the management options required to control weeds, (ii) the weed communities and functions they provide and (iii) the overall performance and sustainability of the implemented land management options. The three components of this framework were analysed in a multidisciplinary project that was conducted on 55 experimental and farmer's fields that included conventional, integrated and organic cropping systems. Our results indicate that the reduction of herbicide use is not antagonistic with crop production, provided that alternative practices are put into place. Herbicide reduction and associated land management modified the composition of in-field weed communities and thus the functions of weeds related to biodiversity and production. Through a long-term simulation of weed communities based on alternative (?) cropping systems, some specific management pathways were identified that delivered high biodiversity gains and limited the negative impacts of weeds on crop production. Finally, the multi-criteria assessment of the environmental, economic and societal sustainability of the 55 systems suggests that integrated weed management systems fared better than their conventional and organic counterparts. These outcomes suggest that sustainable management could possibly be achieved through changes in weed management, along a pathway starting with herbicide reduction.

Herbicide resistance (HR) has been a major management challenge and ongoing threat in cropping regions over several decades, particularly in the time since the widespread adoption of no-tillage cropping systems. Despite extensive and severe development of resistance in Australian cropping regions, growers have been able to maintain control of new weed populations by introducing new herbicides and non-herbicide practices. These integrated weed management (IWM) practices have helped farming systems maintain productivity and adapt to changing environmental and agronomic conditions. Earlier studies found that the adoption of these alternative practices was associated with a reaction to the initial development of forms of HR on a farm. Practices include those classified as harvest weed seed control (HWSC) that kill potentially herbicide resistant weed seeds and reduce overall weed seedbank populations without increasing HR selection pressure. A largely unexplored aspect of the socioeconomics of HR management is whether the initial ‘reactive’ adoption of IWM has a ‘preventative’ effect on the further spread or proliferation of resistance development to other herbicides and in other weed species. To gain a deeper understanding of the farm-scale factors determining the presence of HR, the adoption of IWM practices, and the relationship between IWM use and HR status, we focus on whether initial reactive adoption of IWM has a preventative effect on further resistance development. Data from 602 broadacre grain growers across 13 agroecological zones of Australia were analyzed using Ordinary Least Squares and Logistic regressions to assess the extent of IWM practice adoption, while Ordered Logit models were used to capture the diversity of IWM practice use, including HWSC strategies. Notably, we found that adoption of IWM (including HWSC) was higher in the Western and Southern regions, most likely where HWSC practices can offer greater control on the most common resistant weed types, such as annual ryegrass. There was no evidence to support the argument that IWM use on farms is associated with reduced herbicide use, but there was considerable evidence to show that early forms of HR development on farms have led to the use of IWM practices, such as HWSC, that have the potential to reduce the seed set of weeds with potential new forms of resistance. The extent of HR was the only consistently highly significant variable to explain IWM use. These results have the capacity to pre-emptively identify sustainable weed management scenarios in various regional farming systems and future contexts, including where earlier ‘reactive’ adoption of resistance management practices may now be offering ‘proactive’ benefits. • Examine farm-scale factors influencing IWM and HWSC in Australian cropping systems. • First nationwide farm-level study links HR presence to proactive adoption of IWM practices. • Analysis of 602 growers' data across 13 AEZ using OLS, logistic, and ordered logit models. • HR presence, farm size, no-till years, and advisory support strongly drive IWM uptake, especially in WA & SA. • Evidence-based guidance for regional policymakers to target HR management and support IWM adoption.

Narrow row spacings in peanut (Arachis hypogaea L.) production suppress spotted wilt and promote rapid canopy closure, improving competitiveness with weeds. Trials were conducted from 1999 to 2001 to determine if weed suppression in narrow row spacings, in conjunction with new residual herbicides supplemented with nonresidual herbicides, improved weed control and reduced herbicide use. Within each row spacing were three levels of weed management using the residual herbicides imazapic {(±)‐2‐[4,5‐dihydro‐4‐methyl‐4‐(1‐methylethyl)‐5‐oxo‐1H‐imidazol‐2‐yl]‐5‐methyl‐3‐pyridinecarboxylic acid}, diclosulam [N‐(2,6‐dichlorophenyl)‐5‐ethoxy‐7‐fluoro[1,2,4]triazolo[1,5‐c]pyrimidine‐2‐sulfonamide], sulfentrazone {N‐[2,4‐dichloro‐5‐[4‐(difluoromethyl)‐4,5‐dihydro‐3‐methyl‐5‐oxo‐1H‐1,2,4‐triazol‐1‐yl]phenyl]methanesulfonamide}, and flumioxazin {2‐[7‐fluoro‐3,4‐dihydro‐3‐oxo‐4‐(2‐propynyl)‐2H‐1,4‐benzoxazin‐6‐yl]‐4,5,6,7‐tetrahydro‐1H‐iso‐indole‐1,3(2H)‐dione}. Minimal weed management was ethalfluralin [N‐ethyl‐N‐(2‐methyl‐2‐propenyl)‐2,6‐dinitro‐4‐(trifluoromethyl)ben‐zenamine] alone for annual grass control. Moderate weed management was ethalfluralin, a residual herbicide, and 2,4‐DB [4‐(2,4‐dichlorophenoxy)butanoic acid]. Intense weed management was the moderate system for each residual herbicide, plus paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion), bentazon [3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide], and acifluorfen {5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid}. Peanut seeded in narrow rows had quicker canopy closure than peanut seeded in wide rows. Densities of individual weeds species were not affected, although total weed densities were lower in narrow rows than wide rows. Narrow row spacings with residual herbicides did not reduce herbicide use compared with wide row spacings. Yields were 12% greater in narrow rows than wide rows. While narrow row spacings did not affect individual weed species and reduce herbicide use, narrow row spacings supplement herbicides by reducing the total number of weed escapes.

Enhanced weed control can occur when chemical herbicides are applied in combination with microbial agents. Synergy between chemicals and biologicals was first observed with fungal bioherbicides. Use of a herbicide with a fungal-bioherbicide does not appear to widen the weed spectrum of the bioherbicide but does increase the efficacy. In some cases the synergy may result from a suppression of phytoalexin synthesis by the chemical herbicide. Use of synthetic herbicides to synergize mycoherbicides will in some cases reduce herbicide use rate and improve mycoherbicide efficacy. We report here that synergy occurs between chemical herbicides and bacterial agents. We have discovered that bacteria which cause little or no injury to weeds when applied alone can enhance the stability of low levels of chemical herbicides to control a broad spectrum of weeds. We term this synergistic combination the X-tend system. In the first year of X-tend field trials, the level of weed control required for commercialization was not obtained consistently across geographic locations. Consistency will need to be improved through selection of more robust microbial strains and/or improvements in formulations

Reducing atrazine leaching by integrating reduced herbicide use with mechanical weeding in corn ( Zea mays)

Crop production in the Midwestern U.S. and Vietnam's Mekong Delta requires sustainable and cost effective weed management strategies because both regions are grappling with increasing weed resistance to herbicides, and concerns over environmental damage from herbicides. Agroecological approaches that employ diverse cropping systems to subject weeds to multiple stress and mortality factors may provide reliable weed management that is cost efficient and less reliant on chemicals. Agroecological weed control is based on sound understanding of weed population dynamics, natural resources, and climate attributes, and thus is practical regardless of the level of technology to which farmers have access. We tested the effectiveness of cropping system diversification on weed control in a field experiment conducted in Boone County, Iowa, USA. We compared weed growth in three cropping systems (2-, 3- and 4-year rotation sequences) managed with two herbicide regimes (low and conventional input levels). For a given rotation system, the low herbicide regime, i.e. reduced herbicide inputs coupled with increased mechanical weed control, used 62% and 94% less herbicide active ingredient (kg a.i. ha-1) on corn and soybean, respectively, compared to the conventional regime. Averaged over herbicide regimes, the 3- and 4-year systems reduced herbicide use 33% and 50%, respectively, compared with the 2-year system. In 2014 and 2015, weed biomass was two-fold greater under the low herbicide regime compared with the conventional regime, and six- to seven-fold greater in the 3-year and 4-year rotations than the 2-year rotation. However, increases in weed biomass did not affect corn or soybean yield. We also assessed whether intensity of soil sampling used in previous research was precise enough for measuring weed seedbank density. A soil sampling intensity of ~ 87 cm2/1732 cm3 (surface area/volume), was acceptable for estimating total weed seed density, and soil material from 36 cores taken within one experimental unit could be combined for single processing. Results of our work indicate that multitactic weed management strategies within diversified cropping systems offer opportunities to reduce reliance on herbicides. Nonetheless, additional research is needed for further improvement of non-chemical weed suppression tactics, and for better understanding of the effects of cropping system diversification on weed population and community dynamics.

This series of papers was presented at the Symposium on Integrating Alternative Strategies into Weed Management held during the 1994 ASA‐CSSA‐SSSA annual meetings in Seattle. The program was sponsored by Division A‐8 (Integrated Agricultural Systems) and NCR‐177—a North Central Region technical working group on Non‐Herbicide Alternatives for Weed Management, the Weed Science Society of America, and Divisional co‐sponsors A3, A5, A4, and C3. Executive Summary Weeds are a major problem in production agriculture throughout the world. Weeds have been part of the challenge in maintaining adequate food supplies since agrarian ways of life evolved. In order to maintain yields of plants and animals, weeds must be controlled. In 1992, losses due to weeds in the USA and Canada were estimated at $4.1 billion, with estimated losses exceeding $19 billion if herbicides were not available. However, problems with herbicides, including groundwater and surface water contamination, other offsite movement, and pesticide residues in food, has sparked public awareness and restrictions of herbicide use. These problems have challenged weed scientists to consider alternative and integrated systems of weed management to reduce herbicide inputs and impacts. In order to determine what the term “alternative” weed management strategies represents, one must first define the conventional strategies producers use. If this symposium were presented in the 1950s, we probably would have described chemical‐based strategies that were developed around such organic chemicals as 2,4‐D, simazine, and atrazine, and some inorganic chemicals. Use rates of these chemicals would average about 4 to 6 Ib ai per acre. These herbicides would be presented as an alternative to hand‐pulling, cultivation, more cultivation, and inorganic chemicals applied at rates of 60 to 100 lb/acre. Use of herbicides reduced the number of cultivations and labor needed for effective weed control and allowed an increase in farm size. In fact, farm labor requirements in the USA decreased by 25% from 1947 to 1986, while chemical use increased by 800% (Osteen and Szmedra, 1989). In the 1990s, our conventional strategies for weed management are organic chemical based. The herbicide families used today include some of the older herbicides used in the 1950s including 2,4‐D and the triazines. More recently, herbicide families added to the chemical arsenal include sulfonyl ureas, immidiazilinones, and aryloxyphenoxies. Some of the newer herbicides are used at rates 10 to 100 times lower than the older herbicides. Nevertheless, herbicide use has increased in the USA from 71 million lb ai in 1964 to 456 million lb ai in 1986. Virtually all the acreage of some crops is treated with some herbicide. The application of herbicide saves labor and time, has given excellent control of some of the most persistent weeds, has increased yields, and has allowed the growth of farm sizes. Increased herbicide use has not been without cost or public concern. Producers are being pressured to reduce herbicide use on crops. Government regulations reveal a society concerned with sometimes real and often perceived risks that are associated with herbicides. These risks include: contamination of ground and surface water, herbicide residues that may increase the risk of human or animal health problems, and the harming of already endangered plant species. As agriculture steps into the 21 st century, agricultural scientists must help producers meet the increasing demand for food while providing methods that minimize weed interference (which probably does not equal weed control) and undesirable environmental impact. This does not mean throwing out all herbicides. The “alternative” weed management tactics described in the following technical reports presented at the symposium encompass a range of integrated methods including crop competition, cover crops, mechanical control, and biocontrol agents. Considerations and challenges for developing integrated systems are also discussed, including the governmental policy issues that help or hinder adoption of alternative weed management systems, the need to understand weed biology and ecology to make systems work, and techniques used to develop alternative weed management strategies. Several other topics were considered at the symposium, such as the environmental consequences of weed management, the use of crop rotation, and extension challenges. The symposium drew about 200 participants and featured highly spirited discussions. The day following the symposium, a volunteer session had about 20 posters devoted to alternative weed management strategies in rangeland, crops, and Christmas tree plantations. The following papers provide information on the challenges and guidance on the development of alternative strategies for weed management. Through adoption and modification, we can meet the challenges of today and the hture. On behalf of NCR‐177 and others, we would like to thank all those who contributed to this program. Sharon Clay and Steve Oberle Symposium organizers ( clay@mg.sdstate.edu )

Management in a modified no-tillage corn–soybean–wheat rotation influences weed population and community dynamics

Concerns in the public and agricultural sectors about agricultural practices have led many weed scientists and producers to consider alternative weed management strategies. Weed management practices have been influenced greatly by the availability of selective herbicides for major crops. The impact of herbicides has been so dominating that weed science is often perceived to be the science of herbicides rather than the science of weeds. The general public and many agricultural producers are searching for alternatives to herbicide‐intensive weed management practices. A shift away from dependence on herbicides is complicated by a poor understanding of weed biology and ecology and the availability of few alternative weed control tactics. Education and research efforts have to focus on the application of existing knowledge as well as the development of new fundamental knowledge. Reductions in herbicide use can be attained within the framework of existing management systems. However, given the poor understanding of weeds and lack of control options, new approaches to weed management are needed. Weed scientists have to play a central role in the development of new cropping systems to avoid continuation of reactive approaches to weed control.Research QuestionConcerns over current practices have lead many weed scientists and crop producers to seek alternative strategies for weed control. The goal of these strategies is to develop systems that provide producers with more options for weed control and reduce dependence on tillage and herbicides, thus minimizing the environmental, biological, economic, and societal impacts of controlling weeds. Herbicides have been a valuable tool and have provided benefits to the farm and urban communities. However, weed control has to be viewed as a more integrated science. Refocusing away from overdependance on a single technology (herbicides) will require greater understanding of biological systems than we currently possess.Literature SummaryWeed management is in transition from strict reliance on control of existing problems to placing greater emphasis on prevention of propagule production, reduction of weed emergence in a crop, and minimizing weed competition with the crop. Weed management emphasizes integration of techniques to manage or anticipate problems rather than solving them after they are present. Weed management does not eliminate the need for control nor does it advocate that our best control techniques be abandoned. Its goal is to maximize crop production where appropriate and optimize grower profit by integrating preventative techniques, scientific knowledge, and management skills.Weed control is achieved by physical, chemical, or biological disturbance. All forms of disturbance exert selection pressure and result in the survival and proliferation of the best adapted plants. Several decades of use of modem production practices have not eliminated weeds, but have greatly changed the population dynamics of weed communities. In order to develop new cropping and weed management systems, the impacts of agricultural practices on weeds must be better understood and anticipated.Applied QuestionsAre there practices that growers can implement immediately to reduce herbicide use?Yes. The use of mechanical control operations alone or in combination with herbicide banded over the crop row or reduced rates of herbicide can reduce herbicide use and maintain weed control. Field scouting and record keeping may also lead to more efficient use of herbicides. Weed thresholds and decision aid models may also lead to reduced use.What type of research is needed to develop alternative weed management systems that go beyond current cropping systems?A better understanding of weed biology and ecology is the key. This information will aid in the development of site‐specific management systems and in the redesign of cropping systems. There is also potential for new control practices such as biological control, allelopathic plants, smother plant systems, or more competitive crop cultivars.

Conservation agriculture (CA) appears as a promising agricultural pathway to achieve multiperformance but is currently questioned due to its reliance on herbicides for weed management, especially glyphosate. One limit in the development of CA-based agroecological cropping system less reliant on herbicide use is the strict definition of CA based on technical means (i.e. the three principles) rather than targeted objectives. In this chapter, the authors mobilize research carried out on experimental stations (e.g. CA-SYS platform) and farmer networks (e.g. French DEPHY-farm network) to synthesize knowledge on how herbicide-free no-till agriculture could be achieved. They provide insights on the multiperformance of herbicide-free and nature-based CA systems compared to reference CA systems. Designing cover crops to ensure growth in a context of unpredictable weather conditions and facilitate mechanical termination, and ensuring crop establishment in absence of tillage and herbicides represent major research avenues for the development of pesticide-free CA systems.

The long‐term economic benefits of `patch' spraying are likely to be related to the initial spatial distribution of the target weeds, the demographic characteristics of the species and the weed control and crop husbandry practices to which they are subjected. This paper describes a stochastic simulation model developed to investigate the interaction between weed seed dispersal and patch spraying. Simulated weed plant and seed populations are generated and compared with data from field observations. Lloyd's Patchiness index is used to quantify the patchiness of the weed density distribution, and the parameter k of the negative binomial distribution is used as a measure of distribution shape. A method of assessing the spatial scale of weed aggregation is proposed, in which spatial weed density information is transformed into the frequency domain, using a discrete two‐dimensional Fourier transform. In this paper, we simulate `on/off' patch spraying (full or zero herbicide application rate). A quantitative analysis of the effects of sprayer resolution and weed seed dispersal range on the herbicide reduction and yield benefits from patch spraying is performed for three initial spatial seedbank distributions. The model is parameterized for the grass weed Alopecurus myosuroides Huds. Herbicide is applied in square areas (whose size is defined by the spatial resolution of the sprayer) in which mean weed density is greater than or equal to one plant m–2. For a system conforming to this specification we show that for the control of A. myosuroides, it is unlikely that patch spraying would be profitable in the long term if the control area is larger than 6 m × 6 m. In some circumstances higher resolution may be required.

Gray levels can improve the performance of binary image digitizers

Rice (Oryza sativa L.) is the most important food crop catering half of the world’s population. India being the second largest producer of rice, needs to produce around 120 million tons of rice by 2030 to feed its one and a half billion plus population. Weeds are undoubtedly a major biotic constraint to rice production in most of the rice growing areas of the world. Rice fields are very often characterized by a complex plurispecific weed flora, comprising of grasses, sedges, and broad-leaved weeds (BLWs). They usually grow faster than rice and absorb available water and nutrient earlier than the rice and suppress rice growth. Cultural and mechanical methods of weed management in general, are time consuming, cumbersome and laborious apart from being less effective because of chance of escape and regeneration of weeds from roots or rhizome that are left behind. Herbicides offer the most effective, economical and practical way of weed management. Since rice ecosystems usually harbours a variety of weeds, the use of a single herbicide cannot give satisfactory results. Moreover, continous use of such herbicides leads to the evolution of weeds resistant to several herbicides. Therefore, more convenient option would be single shot application of ready mix or tank mix combination of herbicide. The herbicide mixtures broaden the spectrum of weed control in single application. The ideal herbicide combinations are those that effectively target the weed species while minimizing toxicity to crops, thereby exhibiting enhanced selectivity. Using herbicide combinations allows for reduced herbicide use rates compared to using a single herbicide. Additionally, apart from providing broad-spectrum weed control, herbicide combinations reduce the herbicide load in the environment and minimize application costs. Among the various combination herbicides available, the ones having pre-emergence and post-emergence herbicides combined had shown better weed control with single shot application at reduced cost. Some of the ready-mix herbicide combinations that are gaining greater importance includes Pretilachlor + Pyrazosulfuron-ethyl, Pendimethalin + Penoxsulam and Butachlor + Penoxsulam.