Herbicide Savings Research Articles

Site-Specific Weed Management in Cotton Using WebHADSS™

Field trials were established in 2005 and continued in 2006 to evaluate a conventional broadcast herbicide sprayer compared to a variable spray (sensor-activated) weed-sensing sprayer (WSS). The computer-based Herbicide Application Decision Support System (WebHADSS™) was used to determine a portion of the herbicides applied (based on herbicide efficacy and economics). Weed control, herbicide usage, crop yield, and net returns were compared across treatments. The broadcast applications were usually the most effective at controlling weeds. A PPI herbicide did not always improve weed control compared to treatments in which no PPI herbicide was applied. Variable treatments used less herbicide than the broadcast system in both years. Cotton lint yields in broadcast applications were similar to the weed-free check in both years of the study. Variable treatments often provided equivalent net returns (gross yield revenue less weed control cost) to the broadcast treatments. Although herbicide savings were observed in the variable treatments when compared to a broadcast system, a reduction in weed control was observed, indicating the need for future improvements of this system. A site-specific weed management program used in conjunction with WebHADSS™ may have potential in cotton production systems in the Texas Southern High Plains where weed densities are low.

Ground-based spectral reflectance measurements for evaluating the efficacy of aerially- applied glyphosate treatments

Aerial application of herbicides is a common tool in agricultural field management. The objective of this study was to evaluate the efficacy of glyphosate herbicide applied using aircraft fitted with both conventional and emerging aerial nozzle technologies. A weedy field was set up in a randomised complete block experimental design using three replicates. Four aerial spray technology treatments, electrostatic nozzles with charging off, electrostatic nozzles with charging on, conventional flat-fan hydraulic nozzles and rotary atomisers, were tested. To evaluate the glyphosate efficacy and performance of aerial spray technologies, spectral reflectance measurements were acquired using a ground-based sensing system for all treatment plots. Three measurements were taken at 1, 8, and 17 days after treatment (DAT). The statistical analyses indicated that glyphosate applied with different methods killed the weeds effectively compared to untreated areas at 17 DAT. Conventional flat-fan nozzles and rotary atomisers performed better than the electrostatic nozzles with charging off. There was no evidence to show that the electrostatic nozzle performed better with charging on or charging off. The results could provide applicators with guidance equipment configurations that can result in herbicide savings and optimised applications in other crops.

Sensor-based weed detection and application of variable herbicide rates in real time

An important step towards application of variable herbicide rates is the development of online sensors for detecting weeds. Field trials were conducted with a sensor-controlled field sprayer from the year 2000 to 2003 in cereals and pea. The aim was to quantify the influence of the real-time application of variable herbicide rates on the amount of herbicides used, grain yield and late weed infestation. In 13 field trials average herbicide savings of 24.6% were achieved (cereals: 22.8%, pea: 27.9%), and compared with conventional application on average no yield reduction was caused by sensor-based herbicide application. When late weed infestation was checked shortly before harvest, no differences in weed density were observed between areas with reduced and areas with standard dosage.

Assessing the opportunity for site‐specific management of Avena sterilis in winter barley fields in Spain

SummaryThe abundance of Avena sterilis in dryland barley fields was studied in four Spanish provinces. During two growing seasons, differential geopositioning system (DGPS)‐geo‐referenced A. sterilis infestations were obtained in 31 fields. The majority of the infestations were concentrated in few large but irregularly shaped patches, with a higher number of smaller and more regular patches accounting for a small proportion of the infestation. A multitude of very small and irregular patches completed the inventory. The implications of this spatial structure were studied. Site‐specific adjusted‐dose herbicide application offered 61–74% potential herbicide savings. However, given the low levels of infestation and the low economic returns obtained in most of the provinces, the most profitable strategy was generally no herbicide application. Site‐specific treatments were advantageous only in high‐returns systems. Because few large patches provided the majority of the infestation, zone‐specific treatments would be advisable, until such time that weed detection and site‐specific application technologies become more efficient.

Economics of site-specific weed management

Nascent research on the profitability of site-specific weed management has focused on reduced herbicide use, ignoring significant information costs for scouting, making treatment maps, and patch herbicide application. Including these information costs results in few, if any, studies, fully covering added costs with herbicide savings. Real-time, sensor-driven site-specific herbicide management promises to overcome many of the scouting and map-making costs so long as weed species recognition accuracy continues to improve and commercial capital costs to decline. Two means to increase revenues are possible from site-specific weed management: value-added crop products (e.g., herbicide-free, nontransgenic crops) and environmental stewardship payments from government programs. Site-specific ecological weed management offers a more fruitful means to garner both higher prices from “green” consumers and revenues for sound environmental stewardship. It entails using spatial tools to enhance habitat for weed predators and diseases and their vectors, as well as to grow crops that are better able to compete with weeds. The most economically promising areas for future weed management will draw upon both spatial and developmental management tools.

Performance Study of Variable-rate Herbicide Applications based on Remote Sensing Imagery

Weed control effectiveness and herbicide savings were determined for a variable-rate technology (VRT) herbicide application scenario involving three rates, including 100, 67 and 33% rates. Four herbicide treatments, including the VRT scenario and three blanket applications, were tested over a plot of soya beans with a severe weed problem. In the comparison of VRT and conventional methods, the former achieved the best performance in terms of weed control effectiveness and herbicide use efficiency. However, the particular rate scenario used for VRT applications was shown to have flaws. Specifically, the low rate did not provide adequate weed control even over areas of low weed cover. Also, the medium and high rates performed equally well over areas of high weed cover, indicating that the high rate exceeded the minimum dose required for adequate weed control. Adjustment of the rate scenario is necessary for optimum performance of VRT applications in future experiments. These adjustments may involve changes in the active ingredient application rates, the rate reduction percentages, the number of rates used, or the rate selection criteria. In addition, the results demonstrated the importance of using weed species information in the selection of herbicide dosages.

Aplicação localizada de herbicidas em pós-emergência na cultura de soja

Com o crescimento do interesse pela aplicação localizada de herbicidas, considerando a variabilidade espacial da comunidade das plantas daninhas, torna-se necessário o conhecimento da eficácia dessas aplicações, comparadas com as convencionais, em área total. O experimento foi desenvolvido com o objetivo de avaliar a eficácia de controle das plantas daninhas por meio da aplicação localizada de herbicidas em comparação com a aplicação convencional. Foram escolhidas quatro áreas de 0,5 ha, em duas das quais foi feito o mapeamento da densidade de infestação das plantas daninhas, antes e após a aplicação do herbicida, empregando o método de amostragens numa grade regular de 6 x 6 m, utilizando áreas amostrais de 0,25 m², sendo duas áreas usadas para pulverização convencional e duas áreas com mapeamento das plantas daninhas para a pulverização localizada. As avaliações das infestações das plantas daninhas foram feitas antes e após a aplicação localizada de herbicidas, nos mesmos locais, nas duas avaliações. Foram aplicadas duas doses da mistura formulada dos herbicidas fluazifop butil (125 g L-1) + fomesafen (250 g L-1), sendo a dose de 1,0 L ha-1 da mistura formulada para densidades de plantas daninhas abaixo de 50 plantas m², e a dose de 2,0 L ha-1, para densidades acima de 50 plantas m-2. A comparação da aplicação convencional a 2,0 L ha-1 com a aplicação localizada mostrou economia de herbicidas da ordem de 18 e 44% para as duas áreas estudadas, respectivamente. Foram detectados 55 e 77% das áreas livres de infestação, sendo verificadas nessas áreas densidades muito baixas. Portanto, a aplicação localizada de herbicida realizada neste experimento mostrou que grande economia de produtos é possível mantendo-se a eficácia de controle e, conseqüentemente, reduzindo o impacto ambiental da aplicação convencional com dose média e pulverização em área total.