Volunteer corn in soybean can reduce yields, interfere with harvest, and cause unacceptable levels of contamination by its presence in the harvested soybean. In Ontario, soybean frequently follow corn in rotation. The use of glyphosate-resistant corn and soybean varieties has increased dramatically in Ontario. Field studies were conducted at two locations in southwestern Ontario to determine whether quizalofop-p-ethyl, clethodim, and fenoxaprop-p-ethyl can be tank mixed with glyphosate to provide effective control of volunteer glyphosate-resistant corn in glyphosate-resistant soybean. Soybean plots were overseeded with glyphosate-resistant corn and treatments consisting of glyphosate applied alone and tank mixed with full and reduced rates of each graminicide with and without a recommended surfactant. Tank mixing the graminicides and adjuvants with glyphosate did not affect glyphosate weed control or crop tolerance. Use of a recommended adjuvant significantly improved the effectiveness of the graminicides, particularly when reduced rates were applied. Quizalofop-p-ethyl was the most effective graminicide for controlling glyphosate-resistant volunteer corn, followed by clethodim and fenoxaprop-p-ethyl.

Crop losses from weed interference have a significant effect on net returns for producers. Herein, potential corn yield loss because of weed interference across the primary corn-producing regions of the United States and Canada are documented. Yield-loss estimates were determined from comparative, quantitative observations of corn yields between nontreated and treatments providing greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each state and province provided data from replicated, small-plot studies from at least 3 and up to 10 individual comparisons per year, which were then averaged within a year, and then averaged over the seven years. The resulting percent yield-loss values were used to determine potential total corn yield loss in t ha−1 and bu acre−1 based on average corn yield for each state or province, as well as corn commodity price for each year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across the seven years, weed interference in corn in the United States and Canada caused an average of 50% yield loss, which equates to a loss of 148 million tonnes of corn valued at over U.S.$26.7 billion annually.

Soltani, N., Shropshire, C., Cowan, T. and Sikkema, P. 2003. Tolerance of cranberry beans (Phaseolus vulgaris) to soil applications of s-metolachlor and imazethapyr. Can. J. Plant Sci. 83: 645-648. There is little information on the tolerance of cranberry beans to preplant incorporated (PPI) and preemergence (PRE) applications of s-metolachlor and imazethapyr, either alone or in tank mix combination, for selective weed control in cranberry beans in Ontario. Tolerance of two cranberry bean cultivars, Hooter and SVM Taylor, to PPI and PRE applications of s-metolachlor, imazethapyr and their tank mix combination at the label rate (1×) and twice the label rate (2×) were studied at two Ontario locations (Exeter and Ridgetown) in 2001 and 2002. There were no differences between the two cultivars in their responses to the herbicide treatments. PPI and PRE applications of s-metolachlor alone at the 1× and 2× rate had no effect on visual crop injury and no negative effect on plant height, dry weight and yield compared to the control. The PPI and PRE applications of imazethapyr at the 1× rate did not result in significant visual crop injury, and had no negative effect on bean height and dry weight, but at the 2× rate there was significant visual crop injury, a decrease in height with the PPI application and decreased dry weight with PPI and PRE applications. No negative effect on cranberry bean yield was observed with the application of imazethapyr at either the 1× or 2× rates. The PPI and PRE applications of the tank mix of s-metolachlor plus imazethapyr at the 1× rate did not result in significant visual crop injury or decreases in bean plant height or dry weight. At the 2× rate, there was significant visual crop injury, a decrease in bean plant height with PPI and PRE applications and decreased dry weight with the PPI application. The tank mix of s-metolachlor plus imazethapyr at the 1× rate had no effect on yield, but the PPI application at the 2× rate caused a decrease in yield at 1 of the 4 site-years. Les deux cultivars ont réagi de la même manière aux traitements. L'usage PPI et PRE du s-méto-lachlor aux deux taux d'application n'entraîne pas de dommages visibles à la culture et n'a aucune incidence négative sur la hauteur des plants, le poids sec ni le rendement, comparativement aux témoins. L'usage PPI et PRE d'imazéthapyr au taux 1× n'entraîne pas non plus de dommages visibles importants à la culture et n'a pas d'incidence négative sur la hauteur des plants ni sur le poids sec, mais au double du taux normal, on note d'importants dommages à la culture, les plants sont plus petits avec le traitement PPI et il y a réduction du poids sec avec les traitements PPI et PRE. Le rendement du haricot canneberge n'est affecté par l'imazéthapyr à aucun des deux taux d'application. L'usage PPI et PRE du mélange n'entraîne pas de dommages visibles importants ni de forte diminution de la hauteur des plants et du poids sec au taux d'application normal, mais au double de ce taux, on note des dommages visibles sensibles, une rédu...

Herbicide-resistant crops, such as glyphosate-resistant (GR) soybean, allow for broad-spectrum, flexible weed control with minimal crop injury; however, the development of GR weeds, such as horseweed, has forced reliance on alternative herbicides for control of these weeds. While preplant (PP) herbicides provide excellent control of GR-horseweed, there are currently no POST herbicide control options within soybean. The objective of this study was to evaluate the efficacy of dicamba for the control of GR-horseweed when applied PP, POST, and sequentially in dicamba-resistant soybean. Dicamba applied PP at 600 g a.e. ha−1provided 90 to 100% control of GR-horseweed 8 wk after application (WAA) across three field trials conducted in Ontario in 2011 and 2012. Similarly, sequential applications provided 91 to 100% control. This technology provides a much-needed POST option of dicamba to be applied as a rescue treatment to control weed escapes caused by late emergence or poor initial control following a PP herbicide application.

Weeds are one of the most significant, and controllable, threats to crop production in North America. Monetary losses because of reduced soybean yield and decreased quality because of weed interference, as well as costs of controlling weeds, have a significant economic impact on net returns to producers. Previous Weed Science Society of America (WSSA) Weed Loss Committee reports, as chaired by Chandler (1984) and Bridges (1992), provided snapshots of the comparative crop yield losses because of weeds across geographic regions and crops within these regions after the implementation of weed control tactics. This manuscript is a second report from the current WSSA Weed Loss Committee on crop yield losses because of weeds, specifically in soybean. Yield loss estimates were determined from comparative observations of soybean yields between the weedy control and plots with greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each US state and Canadian province provided at least three and up to ten individual comparisons for each year, which were then averaged within a year, and then averaged over the seven years. These percent yield loss values were used to determine total soybean yield loss in t ha−1and bu acre−1based on average soybean yields for each state or province as well as current commodity prices for a given year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across 2007 to 2013, weed interference in soybean caused a 52.1% yield loss. Based on 2012 census data in the US and Canada soybean was grown on 30,798,512 and 1,679,203 hectares with production of 80 million and 5 million tonnes, respectively. Using an average soybean price across 2007 to 2013 of US $389.81 t−1($10.61 bu−1), farm gate value would be reduced by US $16.2 billion in the US and $1.0 billion in Canada annually if no weed management tactics were employed.

`Crimson Sweet' watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants were grown with various mulches and rowcovers and analyzed for relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area index (LAI), and crop growth rate (CGR). Spunbonded polyester fabric (SB-PF) and perforated polyethylene film (PCP) rowcovers generally showed greater mean RGR, SLA and CGR than spunbonded polypropylene polyamide net (SB-PP), black plus clear combination plastic mulch and black plastic mulch alone. Plants on mulches and under rowcovers showed significant increases in RGR, NAR, and SLA over plants grown in bare soil. Carbon dioxide concentration inside the transplanting mulch holes was nearly twice the ambient CO, concentration. Growth analysis of sampled watermelon plants during early stages of development under various treatments was predictive of crop yield. Plants under SB-PF and PCP rowcovers produced the earliest fruit and the greatest total yield. An asymmetrical curvilinear model for watermelon growth and development based on cardinal temperatures was developed. The model uses hourly averaged temperatures to predict growth and phenological development of `Crimson Sweet' watermelon plants grown with and without rowcovers. Early vegetative growth correlated well with accumulated heat units. Results indicate a consistent heat unit requirement for the `Crimson Sweet' watermelon plants to reach first male flower, first female flower and first harvest in uncovered plants and plants under rowcovers. Greater variability was observed in predicting date of first harvest than first bloom.

Six field trials were conducted over a two-year period (2014, 2015) to determine the level and consistency of glyphosate-resistant (GR) Canada fleabane control with glyphosate plus saflufenacil plus a third tankmix partner. GR Canada fleabane interference reduced soybean yield 73% compared with the weed free control. At 4 and 8 weeks after application (WAA), glyphosate plus saflufenacil provided 99% and 88% control of GR Canada fleabane respectively, and at 8 WAA, reduced GR Canada fleabane density by 96% and biomass by 89%. Glyphosate plus saflufenacil plus dicamba improved the control of GR Canada fleabane to 100% and 97% at 4 and 8 WAA, respectively. At 8 WAA, glyphosate plus saflufenacil plus amitrole reduced GR Canada fleabane density and biomass 99% and 97%, respectively. At 8 WAA, glyphosate plus saflufenacil plus dicamba at 300 or 600 g a.i. ha −1 reduced GR Canada fleabane biomass 97% and 98%, respectively. Tank-mixing dicamba with glyphosate plus saflufenacil applied pre-plant improved control of GR Canada fleabane; however, this caused 14% and 46% crop injury at 2 and 4 WAA, respectively. Soybean yield for saflufenacil alone and saflufenacil tankmix treatments were similar to the weed free control, with the exception of dicamba (600 g a.i. ha −1).

Tolpyralate is a new 4-hydroxyphenyl-pyruvate dioxygenase (HPPD)-inhibiting herbicide for POST weed management in corn; however, there is limited information regarding its efficacy. Six field studies were conducted in Ontario, Canada, over 3 yr (2015 to 2017) to determine the biologically effective dose of tolpyralate for the control of eight annual weed species. Tolpyralate was applied POST at six doses from 3.75 to 120 g ai ha−1and tank mixed at a 1:33.3 ratio with atrazine at six doses from 125 to 4,000 g ha−1. Regression analysis was performed to determine the effective dose (ED) of tolpyralate, and tolpyralate+atrazine, required to achieve 50%, 80%, or 90% control of eight weed species at 1, 2, 4, and 8 wk after application (WAA). The ED of tolpyralate for 90% control (ED90) of velvetleaf, common lambsquarters, common ragweed, redroot pigweed or Powell amaranth, and green foxtail at 8 WAA was ≤15.5 g ha−1; however, tolpyralate alone did not provide 90% control of wild mustard, barnyardgrass, or ladysthumb at 8 WAA at any dose evaluated in this study. In contrast, the ED90for all species in this study with tolpyralate+atrazine was ≤13.1+436 g ha−1, indicating that tolpyralate+atrazine can be highly efficacious at low field doses.