An Imagery-Based Weed Cover Threshold Established Using Expert Knowledge

Weed Science ◽  
2014 ◽  
Vol 62 (1) ◽  
pp. 177-185 ◽  
Author(s):  
Louis Longchamps ◽  
Bernard Panneton ◽  
Marie-Josée Simard ◽  
Gilles D. Leroux
Keyword(s):  
Weed Management ◽  
Operating Characteristic ◽  
Expert Knowledge ◽  
Characteristic Curve ◽  
Threshold Values ◽  
Economic Threshold ◽  
Weed Density ◽  
Economic Thresholds ◽  
Weed Cover ◽  
Curve Method

The implementation of site-specific weed management requires information about weed cover and decision support systems to determine weed cover thresholds and concomitant herbicide rates. Although it is possible to create accurate weed cover maps over large areas, weed cover thresholds have generally been evaluated using tedious weed density counts. To bridge this gap between weed cover obtained by machine vision and the concept of economic threshold, crop advisers specializing in weed scouting were asked to evaluate over 2,500 weed cover images (2 m by 3 m) and determine if a given image would require herbicide application or not. Using the area under the “receiver operating characteristic” curve method, an optimal weed cover threshold was established. The derived economic thresholds ranged from 0.06 to 0.31% weed cover contingent on the level of tolerance of the expert adviser. Although this threshold seems low, it is comparable with economic threshold values based on weed density.

Downy Brome (Bromus tectorum) Interference and Economic Thresholds in Winter Wheat (Triticum aestivum)

Weed Science ◽  
1990 ◽  
Vol 38 (3) ◽  
pp. 224-228 ◽  
Author(s):  
Phillip W. Stahlman ◽  
Stephen D. Miller
Keyword(s):  
Winter Wheat ◽  
Bromus Tectorum ◽  
Yield Loss ◽  
Wheat Yield ◽  
Dry Weight ◽  
Quadratic Equation ◽  
Downy Brome ◽  
Economic Threshold ◽  
Weed Density ◽  
Economic Thresholds

Densities up to 100 downy brome m2were established in winter wheat in southeastern Wyoming and west-central Kansas to quantify wheat yield loss from downy brome interference and to approximate economic threshold levels. A quadratic equation best described wheat yield loss as a function of weed density when downy brome emerged within 14 days after wheat emergence. Densities of 24, 40, and 65 downy brome m2reduced wheat yield by 10, 15, and 20%, respectively. Wheat yield was not reduced when downy brome emerged 21 or more days later than wheat. Economic thresholds varied with changes in downy brome density, cost of control, wheat price, and potential wheat yield. In a greenhouse experiment, dry weight of 72-day-old wheat plants grown in association with downy brome was not affected by the distance between the weeds and wheat, whereas downy brome plant dry weight increased with increasing distance between the weeds and wheat.

scholarly journals Stratified Threshold Values of QuantiFERON Assay for Diagnosing Tuberculosis Infection in Immunocompromised Populations

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Haruyuki Ariga ◽  
Hideaki Nagai ◽  
Atsuyuki Kurashima ◽  
Yoshihiko Hoshino ◽  
Syunsuke Shoji ◽  
...  
Keyword(s):  
Operating Characteristic ◽  
Characteristic Curve ◽  
Latent Tuberculosis ◽  
Absolute Number ◽  
Threshold Values ◽  
Risk Of Progression ◽  
Healthy Control ◽  
Ifn Γ ◽  
The Relationship ◽  
Hiv Negative

Background. The detection of latent tuberculosis (TB) is essential for TB control, but T-cell assay might be influenced by degree of immunosuppression. The relationship between immunocompetence and interferon (IFN)-γ response in QuantiFERON-TB Gold (QFT) is uncertain, especially in HIV-negative populations.Methods and Results. QFT has been performed for healthy subjects and TB suspected patients. Of 3017 patients, 727 were diagnosed as pulmonary TB by culture. The absolute number of blood lymphocyte in TB patients was significantly associated with QFT. Definitive TB patients were divided into eight groups according to lymphocyte counts. For each subgroup, receiver operating characteristic curve analysis was conducted from 357 healthy control subjects. The optimal cut-off for the patient group with adequate lymphocyte counts was found, but this was reduced for lymphocytopenia.Conclusions. The lymphocyte count was positively associated with QFT. Positive criteria should be calibrated in consideration of cell-mediated immunocompetence and risk of progression to active TB.

Impact of common ragweed (Ambrosia artemisiifolia) aggregation on economic thresholds in soybean

Weed Science ◽  
2003 ◽  
Vol 51 (6) ◽  
pp. 947-954 ◽  
Author(s):  
Michael J. Cowbrough ◽  
Ralph B. Brown ◽  
François J. Tardif
Keyword(s):  
Moisture Content ◽  
Field Experiments ◽  
Yield Loss ◽  
Ambrosia Artemisiifolia ◽  
Threshold Values ◽  
Economic Threshold ◽  
Common Ragweed ◽  
Economic Thresholds ◽  
Significant Difference ◽  
Loss Models

One approach to site-specific weed control is to map weeds within a field and then divide the field area into smaller grid units. The decision to apply a herbicide to individual grid units, or decision units, is made by using yield loss models to establish an economic threshold level. However, decision units often contain weed populations with aggregated distributions. Many yield loss models have not considered this because experiments dealing with weed–crop competition typically assume uniform weed distributions. Therefore, these models may overestimate yield losses. Field experiments conducted in 1999 and 2000 compared the effects of common ragweed having a uniform distribution vs. an aggregated distribution on soybean seed yield, moisture content, and dockage. Field experiment data were used to calculate and compare economic thresholds for both distributions. Economic thresholds that considered drying costs and dockage also were compared. There was no significant difference inIparameters (yield loss as density approaches zero) between the two ragweed distributions in either year. Seed moisture content and dockage increased with increasing common ragweed densities, but increases were not significant at the break-even yield loss level. Economic threshold values were similar for both distributions with differences between aggregated and uniform of 0.14 and 0.01 plants m−2in 1999 and 2000, respectively. The economic threshold values were reduced by 0.01 to 0.06 plants m−2when drying costs and dockage were considered.

Canopy Measurements as Predictors of Weed-Crop Competition

Weed Science ◽  
1996 ◽  
Vol 44 (3) ◽  
pp. 511-516 ◽  
Author(s):  
J. I. Vitta ◽  
C. Fernandez Quintanilla
Keyword(s):  
Leaf Area ◽  
Crop Yield ◽  
Weed Management ◽  
Yield Losses ◽  
Weed Density ◽  
Damage Coefficient ◽  
Relative Damage ◽  
Weed Cover ◽  
Better Than ◽  
Crop Competition

The development of weed management systems requires accurate prediction of weed-crop competition. In this paper, simple regression models of crop yield losses based on weed density and weed leaf area are compared. In weed leaf area models, variations in the relative damage coefficient (q) were also analyzed. Finally, three simple methods to assess weed cover were compared: visual, photographic, and optic device assessment. Leaf area models were at least as accurate as weed density models. However, the generality of the leaf area models was restricted by changes in q, according to the date of leaf area evaluation and the year. Although all methods to assess weed cover correlated adequately with weed leaf area, visual estimates were the best to predict crop yield losses perhaps because very low levels of weed leaf area could be distinguished visually better than by other methods.

Volunteer Barley Interference in Spring Wheat Grown in a Zero-Tillage System

Weed Science ◽  
2007 ◽  
Vol 55 (1) ◽  
pp. 70-74 ◽  
Author(s):  
John T. O'Donovan ◽  
K. Neil Harker ◽  
George W. Clayton ◽  
Linda M. Hall ◽  
Jason Cathcart ◽  
...  
Keyword(s):  
Spring Wheat ◽  
Field Experiments ◽  
Yield Loss ◽  
Wheat Yield ◽  
High Rate ◽  
Initial Slope ◽  
Threshold Values ◽  
Economic Threshold ◽  
Economic Thresholds ◽  
The Impact

There is no published information on the impact of volunteer barley on wheat yield loss or on the economics of controlling barley with a herbicide. With the registration of imazamox-resistant wheat, it is now possible to control volunteer barley in wheat. Thus, the likelihood of growing wheat in rotation with barley may increase. Field experiments were conducted in 2003 and 2004 at Beaverlodge, Lacombe, and Edmonton, AB, Canada, and Saskatoon, SK, Canada, to determine the impact of volunteer barley on yield of imazamox-resistant spring wheat seeded at relatively low (100 kg ha−1) and high (175 kg ha−1) rates. Barley was seeded at different densities to simulate volunteer barley infestations. Regression analysis indicated that wheat-plant density influenced the effects of volunteer barley interference on wheat yield loss, economic threshold values, and volunteer barley fecundity among locations and years. Economic thresholds varied from as few volunteer barley plants as 3 m−2at Beaverlodge in 2003 and 2004 to 48 m−2at Lacombe in 2003. In most cases, wheat yield loss and volunteer barley fecundity were lower and economic thresholds were higher when wheat was seeded at the higher rate. For example, averaged over both years at Beaverlodge initial slope values (percentage of wheat yield loss at low barley density) were 4.5 and 1.7%, and economic threshold values of volunteer barley plants were 3 m−2and 8 m−2at low and high wheat seeding rates, respectively. Results indicate that volunteer barley can be highly competitive in wheat, but yield losses and wheat seed contamination due to volunteer barley can be alleviated by seeding wheat at a relatively high rate.

scholarly journals Effect of weed management practices on weed cover in field pea (pisum sativum l.)

2021 ◽  
Vol 9 (1-2) ◽  
pp. 9-14
Author(s):  
István Kristó ◽  
Melinda Tar ◽  
Katalin Irmes ◽  
Marianna Vályi-Nagy ◽  
Attila Rácz ◽  
...  
Keyword(s):  
Pisum Sativum ◽  
Weed Management ◽  
Management Practices ◽  
Agricultural Research ◽  
Great Part ◽  
Growing Season ◽  
Field Pea ◽  
Weed Density ◽  
Pisum Sativum L ◽  
Weed Cover

Field pea (Pisum sativum L.) are planted on small area in Hungary, although it is a precious source of protein (22-28%), and it also plays a significant role like a component in fodder mixture and green forage. It is a great part in crop rotation as a short growing-season legume. Furthermore, it has beneficial effects of nitrogen-fixing nodules being able to obtain N derived from air. One of the most critical limiting factors is to find out weed management practise for control of weeds in field pea. Our field experiment was carried out on site of the National Agricultural Research and Innovation Centre, the Department of Field Crops Research in Öthalom for comparing weed management strategies by evaluate their efficacy and weed flora. We used 6 herbicides or herbicid combination and observed weed density in 5 times during the growing season. The most important weeds were: common chickweed (Stellaria media), wild mustard (Sinapis arvensis), branching lackspur (Consolida regalis), meldweed (Chenopodium album). Among the treatments the highest weed cover was the weedy check, followed by Stomp Super, obtained maximum weed control and long lasting effect. With the application of Basagran 480 SL and Pulsar 40 SL have a significantly lower weed density was recorded than preemergence applications. In case of Corum application, it was the lowest weed cover of all even at harvesting time. According to our experiments use of Dash does not control weeds considerably.

scholarly journals Soybean yield loss and economic thresholds due to glyphosate resistant hairy fleabane interference

2018 ◽  
Vol 84 (0) ◽  
Author(s):  
Dirceu Agostinetto ◽  
Diecson Ruy Orsolin da Silva ◽  
Leandro Vargas
Keyword(s):  
Yield Loss ◽  
Development Stage ◽  
Control Measures ◽  
Economic Threshold ◽  
Economic Management ◽  
Soybean Yield ◽  
Weed Density ◽  
Economic Thresholds ◽  
Soybean Price ◽  
Hairy Fleabane

ABSTRACT: The interference of glyphosate resistant hairy fleabane (Conyza bonariensis) has caused yield losses in soybean crop. Knowledge of the economic threshold is an important aspect for the economic management of resistant weeds. Because of it, the interference of the glyphosate resistant hairy fleabane density on the soybean yield loss was evaluated, as well as to estimate the economic threshold. Two experiments were conducted to verify the effect of different weed densities on the yield of two soybean cultivars (BRS Estância and BMX Turbo). Weed density ranged from 0 to 124 plants m-2. The yield of the BRS Estância decreased by 1.4% to the increase of one single plant, while for the BMX Turbo the loss was 25.9%. Soybean yield and economic threshold were lower for the BMX Turbo cultivar compared to the cultivar BRS Estância, which can be attributed to the genotype, competitive ability, weed development stage and/or environment. Increases in crop yield expectation, soybean price and herbicide efficiency reduce the economic threshold, indicating that the adoption of control measures should be taken when the weed density is low. Due to the high cost of hairy fleabane control, it is only feasible at high densities.

Validation of a Management Program Based on A Weed Cover Threshold Model: Effects on Herbicide Use and Weed Populations

Weed Science ◽  
2009 ◽  
Vol 57 (2) ◽  
pp. 187-193 ◽  
Author(s):  
Marie-Josée Simard ◽  
Bernard Panneton ◽  
Louis Longchamps ◽  
Claudel Lemieux ◽  
Anne Légère ◽  
...  
Keyword(s):  
Seed Production ◽  
Crop Yield ◽  
Weed Management ◽  
Crop Yields ◽  
Threshold Model ◽  
Management Program ◽  
Weed Seed ◽  
Weed Density ◽  
Weed Cover ◽  
Herbicide Use

Weed management decisions based on weed threshold models offer the opportunity to reduce herbicide use by allowing the possibility of forgoing treatment or lowering rates. Weed thresholds based on a relative leaf-cover model were tested during a 4-yr period at two locations. Two 1.62-ha fields, planted to conventional and glyphosate-resistant corn (2004, 2005, 2007) or soybean (2006), were divided in 900 m2sections. Herbicides were applied postemergence to each of these sections with either variable rates based on weed thresholds, or constant full rates. Variable herbicide rates included: no application, half rate, or full rate. Relative weed cover values of 0.2 and 0.4 (corn) or 0.1 and 0.3 (soybean) served as thresholds for incremental rates. Digital images were used to evaluate the relative weed cover. Weed density was assessed before and after herbicide application. Weed seed production was estimated for two species in 2004 and 2005. No difference in crop yield, relative weed cover, weed density, or weed seed production was observed between conventional and glyphosate-resistant cropping systems. During the first year, herbicide use reduction was obtained (−85.4%) with marginal crop yield loss (5 to 15%). In the subsequent 3 yr, preherbicide weed densities increased and concomitant increases in relative weed cover values did not allow more than a 10% overall reduction in herbicide use. This threshold model designed to maintain crop yields within a given year did not allow significant reduction in herbicide use during the following 3 yr. Residual weed populations most likely replenished the seed bank to levels that allowed weed densities to increase afterward. Increased weed density over time in plots treated with full rates of herbicide every year also indicated that a single postemergence herbicide treatment was not sufficient to contain weed populations at low levels every year in this corn–soybean rotation.

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