Roland Gerhards

The Economic Impact of Site-Specific Weed Control

In order to evaluate economic and ecological benefits, site-specific weed control was realised in a 4-year experiment on five fields with a GPS-guided sprayer. An average of 54% of the herbicides could be saved. Savings were strongly dependent on crop and year. For grass weed herbicides, the savings were 90% in winter cereals, 78% in maize, and 36% in sugar beet. For herbicides against broadleaf weeds, 60% were saved in winter cereals, 11% in maize, and 41% in sugar beet. The monetary savings resulting from the reduction in herbicide use varied between the crops, depending on the amount of herbicides saved and the price of the herbicides. In maize, savings of 42euro/ha were realised, in winter wheat of 32euro/ha, in winter barley of 27euro/ha and in sugar beet of 20euro/ha. Large sections of the fields needed herbicide treatment significantly less frequently. In those areas where weed density remained below the weed control threshold, flora and fauna were allowed to establish largely without disturbance.

Precision Crop Protection - the Challenge and Use of Heterogeneity

Precision farming is an agricultural management system using global navigation satellite systems, geographic information systems, remote sensing, and data management systems for optimizing the use of nutrients, water, seed, pesticides and energy in heterogeneous field situations. This book provides extensive information on the state-of-the-art of research on precision crop protection and recent developments in site-specific application technologies for the management of weeds, arthropod pests, pathogens and nematodes. It gives the reader an up-to-date and in-depth review of both basic and applied research developments. The chapters discuss I) biology and epidemiology of pests, II) new sensor technologies, III) applications of multi-scale sensor systems, IV) sensor detection of pests in growing crops, V) spatial and non-spatial data management, VI) impact of pest heterogeneity and VII) precise mechanical and chemical pest control.

Site-Specific Weed Control in Maize, Sugar Beet, Winter Wheat, and Winter Barley

A four-year study of site-specific weed control is presented in this paper. Weed seedling distribution was sampled and mapped prior to and after post-emergence herbicide application in four fields planted with maize, sugar beets, winter wheat and winter barley, rotating on one site. Herbicides and other weed control strategies were applied site-specifically according to the spatial variation of weed populations. Different decision algorithms were used for chemical weed control methods in each crop. A weed treatment map was created to direct location and dosage of herbicide application. The sprayer was coupled with a differential Global Positioning System (DGPS). The solenoid valves of the sprayer were opened automatically when the tractor entered a weed patch characterized in the weed treatment map. For site specific herbicide application, a patch sprayer was developed that allowed variable rate application and the selective control of each section of the spray boom.

An Ultrasonic System for Weed Detection in Cereal Crops

Site-specific weed management requires sensing of the actual weed infestation levels in agricultural fields to adapt the management accordingly. However, sophisticated sensor systems are not yet in wider practical use, since they are not easily available for the farmers and their handling as well as the management practice requires additional efforts. A new sensor-based weed detection method is presented in this paper and its applicability to cereal crops is evaluated. An ultrasonic distance sensor for the determination of plant heights was used for weed detection. It was hypothesised that the weed infested zones have a higher amount of biomass than non-infested areas and that this can be determined by plant height measurements. Ultrasonic distance measurements were taken in a winter wheat field infested by grass weeds and broad-leaved weeds. A total of 80 and 40 circular-shaped samples of different weed densities and compositions were assessed at two different dates. The sensor was pointed directly to the ground for height determination. In the following, weeds were counted and then removed from the sample locations. Grass weeds and broad-leaved weeds were separately removed. Differences between weed infested and weed-free measurements were determined. Dry-matter of weeds and crop was assessed and evaluated together with the sensor measurements. RGB images were taken prior and after weed removal to determine the coverage percentages of weeds and crop per sampling point. Image processing steps included EGI (excess green index) computation and thresholding to separate plants and background. The relationship between ultrasonic readings and the corresponding coverage of the crop and weeds were assessed using multiple regression analysis. Results revealed a height difference between infested and non-infested sample locations. Density and biomass of weeds present in the sample influenced the ultrasonic readings. The possibilities of weed group discrimination were assessed by discriminant analysis. The ultrasonic readings permitted the separation between weed infested zones and non-infested areas with up to 92.8% of success. This system will potentially reduce the cost of weed detection and offers an opportunity to its use in non-selective methods for weed control.

Potential use of ground‐based sensor technologies for weed detection

Site-specific weed management is the part of precision agriculture (PA) that tries to effectively control weed infestations with the least economical and environmental burdens. This can be achieved with the aid of ground-based or near-range sensors in combination with decision rules and precise application technologies. Near-range sensor technologies, developed for mounting on a vehicle, have been emerging for PA applications during the last three decades. These technologies focus on identifying plants and measuring their physiological status with the aid of their spectral and morphological characteristics. Cameras, spectrometers, fluorometers and distance sensors are the most prominent sensors for PA applications. The objective of this article is to describe-ground based sensors that have the potential to be used for weed detection and measurement of weed infestation level. An overview of current sensor systems is presented, describing their concepts, results that have been achieved, already utilized commercial systems and problems that persist. A perspective for the development of these sensors is given.

Discriminating Crop, Weeds and Soil Surface with a Terrestrial LIDAR Sensor

In this study, the evaluation of the accuracy and performance of a light detection and ranging (LIDAR) sensor for vegetation using distance and reflection measurements aiming to detect and discriminate maize plants and weeds from soil surface was done. The study continues a previous work carried out in a maize field in Spain with a LIDAR sensor using exclusively one index, the height profile. The current system uses a combination of the two mentioned indexes. The experiment was carried out in a maize field at growth stage 12–14, at 16 different locations selected to represent the widest possible density of three weeds: Echinochloa crus-galli (L.) P.Beauv., Lamium purpureum L., Galium aparine L.and Veronica persica Poir.. A terrestrial LIDAR sensor was mounted on a tripod pointing to the inter-row area, with its horizontal axis and the field of view pointing vertically downwards to the ground, scanning a vertical plane with the potential presence of vegetation. Immediately after the LIDAR data acquisition (distances and reflection measurements), actual heights of plants were estimated using an appropriate methodology. For that purpose, digital images were taken of each sampled area. Data showed a high correlation between LIDAR measured height and actual plant heights (R2 = 0.75). Binary logistic regression between weed presence/absence and the sensor readings (LIDAR height and reflection values) was used to validate the accuracy of the sensor. This permitted the discrimination of vegetation from the ground with an accuracy of up to 95%. In addition, a Canonical Discrimination Analysis (CDA) was able to discriminate mostly between soil and vegetation and, to a far lesser extent, between crop and weeds. The studied methodology arises as a good system for weed detection, which in combination with other principles, such as vision-based technologies, could improve the efficiency and accuracy of herbicide spraying.

Mechanical Weed Control

Side effects of herbicides and increasing prevalence of organic farming induce the need of further developments in mechanical weed control. Mechanical weed control is mainly associated with cultivating tillage (e.g. tertiary tillage), but also primary and secondary tillage influence weeds. Cultivating tillage is performed in growing crops with harrows , hoes , brushes and a number of special tools for intra-row weed control. Inter-row cultivations have been used in many decades in row crops and perform in general well. To increase their capacity and accuracy, guidance systems are important to steer the hoes along the rows. The success of inter- and intra-row cultivation is highly influenced by selectivity factors. The control mechanisms of all cultivating tillage methods are burring in soil, uprooting, and tearing plants into pieces. Especially for whole crop and intra-row cultivators, successful weed control is highly influenced by appropriate adjustment of the intensity (aggressiveness) of cultivation according to the variations of soil resistance, crop and weed resistance to cultivation and the competitive interactions between crop and weeds. Site-specific weed management aims to identify the spatial and temporal variability of weeds and manage them correspondingly. New technologies for sensing crops and weeds in real-time and robotics allow a precise operation of mechanical tools, to improve efficacy of control and reduce operation costs. Hence in this chapter, implements for mechanical weeding are described together with their options for site-specific weed control strategies. Harrows and rotary hoes are used for whole crop treatment, but it is essential to find the right timing and intensity to obtain the best selectivity and yield response. Different implements attached to the same vehicle are combined together attempting more selective weed control, like the in-row cultivator, the rotary harrow , and the precision hoe . Lately, there are prototypes intending automatic adjustment of the aggressiveness for the spring-tine harrow and autonomous guidance for hoes, thus getting closer to a real-time site-specific weed management approach.

Two-Year Weed Seedling Population Responses to a Post-Emergent Method of Site-Specific Weed Management

Field experiments were conducted to determine how a site-specific weed management practice in Zea mays L. influenced the numerical and spatial distribution of a naturally occurring weed infestation in Z. mays and the succeeding Beta vulgaris L. crop. Compared to conventional broadcast herbicide applications, site-specific herbicide applications reduced herbicide load by 11.5 and 98.0% in two separate Z. mays fields. The broad range in outcomes was attributed to the spatial aggregation and density of target weed populations. While herbicide use was successfully reduced at field locations with low weed density, most survivors of multiple control tactics were in locations with the highest initial density. A greater understanding of interactions between weed management and weed density would increase the likelihood that site-specific weed management offers long-term improvements over conventional approaches.

Determination of the Critical Period for Weed Control in Corn

Abstract Field experiments were conducted in western Atakora, Benin, to determine the critical time period of weed competition in hand-weeded corn. Weeds were removed until different crop growth stages and then allowed to reemerge. Other treatments began weed control at different growth stages (four-, eight-, and ten-leaf stages and flowering) and were maintained until harvest. One treatment was permanently kept weed-free and one treatment was uncontrolled until harvest. Yields without weed competition ranged from 2.8 to 3.4 t ha−1. As expected, yield loss increased with duration of weed infestation and ranged from 38 to 65% compared to permanent weed-free plots. In three out of four site-years, the critical period for weed control started at the four- to six-leaf stage and continued until ten-leaf stage or flowering of corn. Approximately four hand-weeding applications were required in this critical period of weed control. Nomenclature: Corn, Zea mays L. Resumen Se realizaron experimentos de campo en el oeste de Atakora, Benin, para determinar el período crítico de competencia de malezas en maíz manejado con deshierba manual. Las malezas fueron removidas durante diferentes estados de desarrollo del cultivo y luego se les dejó re-emerger. Otros tratamientos iniciaron el control de malezas en diferentes estados de desarrollo (cuatro, ocho y diez hojas y floración) y luego se mantuvieron libres de malezas hasta la cosecha. Un tratamiento fue mantenido libre de malezas permanentemente y otro tratamiento no tuvo control de malezas hasta la cosecha. Los rendimientos sin competencia de malezas fueron de 2.8 a 3.4 t ha−1. Como se esperaba, la pérdida de rendimiento incrementó con la duración de la infestación de malezas y varió entre 38 y 65% al compararse con las parcelas libres de malezas. En tres de los cuatro sitios-años, el período crítico para el control de malezas inició entre los estados de cuatro a seis hojas y continuó hasta el estado de 10 hojas o de floración del cultivo. Aproximadamente, cuatro deshierbas manuales fueron requeridas en este período crítico de control de malezas.

Investigations on herbicide resistance in European silky bent grass (Apera spica-venti) populations

In this study, the results of two-year investigations on herbicide resistance in silky bent grass (Apera spica-venti) populations are presented. Whole-plant bioassays were conducted with different herbicides on over 250 A. spica-venti populations from Central and Eastern European agricultural fields where herbicides failed to achieve satisfactory control. Results showed that over 60% of the suspected populations could be rated resistant to acetolactate synthase (ALS)-inhibitors, resistance to acetyl-CoA (ACCase)-inhibitors could be observed in only a few cases and no resistance to photosystem II (PSII)-inhibitors was detected. Dose-response experiments conducted in the greenhouse on resistant populations with the herbicides flupyrsulfuron-methyl, mesosulfuron+iodosulfuron and fenoxaprop-P-ethyl revealed resistance factors at ED50 and ED90 ranging respectively from 11 to 142, from 2 to 15 and from 4 to 6, thus confirming the prevalence of resistance to ALS-inhibitors in A. spica-venti. In greenhouse experiments, percentage canopy cover after herbicide treatment was determined in susceptible and resistant populations for the herbicides sulfosulfuron and fenoxaprop-P-ethyl by using digital image analysis. A significant effect of herbicide dose on canopy cover was observed in susceptible plants 7 and 15 days after treatment with sulfosulfuron, as well as in all populations when treated with fenoxaprop-P-ethyl. Canopy cover correlated significantly with plant dry weight in all populations, thus indicating that digital image analysis may represent a valid alternative approach to whole-plant bioassays and dose-response analysis for estimating biomass reduction after herbicide treatment. This work provides weed scientists with reliable tools for the verification of herbicide resistance in suspected weed populations.