Weed Control with Halosulfuron Applied Preplant Incorporated, Preemergence or Postemergence in White Bean

Four field trials were conducted over a three-year period (2011-2013) at various locations in Ontario to evaluate the level of weed control provided by halosulfuron applied PPI,PREor POST at 17.5, 35 and 70 g&middotai&middotha-1 in white bean. Halosulfuron applied PPI or PRE at 17.5, 35 and 35 g&middotai&middotha-1 caused 2% or less visible injury 1 and 4 WAA in white bean. However, halosulfuron applied POST at 17.5, 35 and 70 g&middotai&middotha-1 caused 2% - 8% and 1% - 3% white bean injury at 1 and 4 WAA, respectively. There was no decrease in white bean seed yield relative to the weed free check due to weed interference with halosulfuron applied PPI or PRE at doses evaluated, except when applied PRE at 17.5 g&middotai&middotha-1 which resulted in a decrease in seed yield of 25%. Weed interference caused a decrease in white bean yield of 47%, 42% and 44%, when halosulfuron was applied POST at 17.5, 35 and 70 g&middotai&middotha-1, respectively. Halosulfuron applied PPI, PRE and POST controlled AMARE 92% - 100%, 85% - 99% and 47% - 75%;CHEAL 95% - 100%, 83% - 99% and 36% - 51%;and SINAR 97% - 100%, 99% - 100% and 100%, respectively. Halosulfuron applied PPI and PRE reduced AMARE density 93% - 97% and 75% - 95%;CHEAL density 89% - 98% and 81% - 93%;and SINAR density 99% - 100% and 99% - 100%, respectively. Halosulfuron applied PPI and PRE reduced dry weight of AMARE 96% - 98% and 86% - 96%;CHEAL 96% - 98% and 87% - 93%;and SINAR 100% and 100%, respectively. Halosulfuron applied POST at rates evaluated reduced SINAR density and dry weight 100% but caused no significant reduction in AMARE and CHEAL density or dry weight compared to the weedy check. Based on these results, halosulfuron applied PPI orPREat 35 g&middotai&middotha-1 can be used safely for the control of selected broadleaf weeds in white bean production.

Preplant and Postemergence Control of Glyphosate-Resistant Giant Ragweed in Corn

Glyphosate-resistant (GR) giant ragweed has recently been identified in southwestern Ontario and has the potential to be a significant problem for regional corn producers. Eight field trials [four with preplant (PP) and four with postemergence (POST) herbicides] were conducted from 2013 to 2014 on various Ontario farms infested with GR giant ragweed to determine the efficacy of PP and POST tank-mixes in corn. Glyphosate tank-mixed with atrazine, dicamba, dicamba/atrazine, mesotrione plus atrazine, flumetsulam, isoxaflutole plus atrazine, saflufenacil/dimethenamid-P, S-metolachlor/atrazine and rimsulfuron applied PP provided up to 54%, 95%, 93%, 95%, 40%, 89%, 91%, 50% and 93% control of GR giant ragweed and reduced dry weight 69%, 100%, 99%, 100%, 30%, 92%, 98%, 66% and 99%, respectively. POST application of glyphosate alone and tank-mixed with 2,4-D ester, atrazine, dicamba, dicamba/diflufenzopyr, dicamba/atrazine, bromoxynil plus atrazine, prosulfuron plus dicamba, mesotrione plus atrazine, topramezone plus atrazine, tembotrione/thiencarbazone-methyl and glufosinate provided up to 31%, 84%, 39%, 94%, 89%, 86%, 83%, 78%, 72%, 43%, 63% and 58% GR giant ragweed and reduced dry weight 55%, 99%, 72%, 99%, 99%, 98%, 96%, 96%, 93%, 89%, 91% and 95%, respectively. In general, PP control of GR giant ragweed was greater than POST applied herbicides evaluated. Based on these results, glyphosate tank-mixes containing dicamba or mesotrione plus atrazine applied PP, and dicamba applied POST will provide the most consistent control of GR giant ragweed in corn.

Glyphosate-Resistant Giant Ragweed(Ambrosia trifida L.):2,4-D Dose Response and Control with Postemergence Herbicides in Soybean

Glyphosate resistant giant ragweed is an increasing problem in glyphosate resistant cropping systems in southwestern Ontario. The postemergence herbicides registered for use in soybean in Ontario do not provide consistent control of glyphosate resistant giant ragweed. There is limited research on the lowest effective rate of 2,4-D for the control of glyphosate resistant giant ragweed. Consequently, the objectives of this study were a) to determine the efficacy of herbicides applied postemergence for the control of glyphosate resistant giant ragweed in glyphosate resistant soybean, and b) to determine the lowest effective rate of 2,4-D for the control of glyphosate-resistant giant ragweed. Ten postemergence herbicide combinations and seven rates of 2,4-D were evaluated in field studies conducted in 2011 and 2012 at six locations confirmed with glyphosate-resistant giant ragweed. The post emergence herbicides evaluated did not provide acceptable/consistent control. Of the herbicides evaluated, glyphosate plus cloransulam-methyl provided 26% to 70% control 8 WAA of glyphosate resistant giant ragweed, which was the best of the herbicides combinations evaluated. The doses of 2,4-D required to reduce giant ragweed shoot dry weight by 50, 80 and 95% were 142, 310 and 1048 g a.e. ha-1, respectively.

Effect of imazethapyr application timing in kidney and white bean

A total of twelve field trials (6 with kidney bean and 6 with white bean) were conducted over a three-year period (2010 to 2012) at various locations in Ontario to evaluate the tolerance of kidney and white bean to imazethapyr applied preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) at 37.5, 75 and 150 g·ai·ha-1. Imazethapyr applied PPI or PRE in kidney or white bean caused 0%-1%, 0%-4%, and 0%-9% injury at 1, 2, and 4 weeks after application (WAA), respectively. However, the injury was transient and had no adverse effect on shoot dry weight, height, seed moisture content, and yield of kidney or white bean except for shoot dry weight which was reduced 32% with imazethapyr applied PPI compared to the weed free control in white bean. Imazethapyr applied POST in kidney or white bean caused as much as 17%, 18%, and 11% injury at 1, 2, and 4 WAA, respectively. There was no adverse effect on shoot dry weight, height, seed moisture content, and yield of kidney or white bean except for imazethapyr applied POST which increased seed moisture content 1.9% compared to the weed free control in white bean. Based on these results, there is an adequate margin of crop safety in dry bean to imazethapyr applied PPI or PRE at 37.5 or 75 g·ai·ha-1 in kidney and white beans. However, there is not an adequate margin of crop safety for imazethapyr applied POST at rates higher than 37.5 g·ai·ha-1 in kidney and white bean.

Efficacy of 2,4-D Choline/Glyphosate Dimethylamine on Glyphosate Resistant Canada Fleabane (<i>Conyza canadensis</i>) at Different Sizes

Glyphosate resistant (GR) Canada fleabane has spread quickly across southwestern Ontario and new strategies for the control of this competitive weed must be developed especially in no-tillage crops. A premix of 2,4-D choline and glyphosate dimethylamine (DMA) has been developed for application on tolerant corn, soybean and cotton crops that provides an option for the control of this problematic GR weed. The objective of this research was to determine the required dose needed to effectively control GR Canada fleabane at different size categories in field and greenhouse experiments. In the field experiments, nine rates of 2,4-D choline/glyphosate DMA (53.8 to 13,760 g·ae·ha-1) were applied to GR Canada fleabane that were 10 cm in diameter/tall, 20 cm tall or 30 cm tall. Similarly, in the greenhouse, seven rates of 2,4-D choline/glyphosate DMA (0 to 3440 g·ae·ha-1) were applied to 10, 20 and 30 cm tall GR Canada fleabane plants. The three different size classes of GR Canada fleabane responded similarly to 2,4-D choline/glyphosate DMA in the field experiment. In the greenhouse there were some differences in control for the three size classes of GR Canada fleabane with 2,4-D choline/glyphosate DMA;the 20 and 30 cm tall plants required similar rates to provide equivalent control, but the 10 cm plants required a lower rate. In all situations, greater than 1720 g·ae·ha-1 of 2,4-D choline/glyphosate DMA was required to provide 95% control of 10, 20 and 30 cm tall Canada fleabane in greenhouse (35 DAA) and field experiments (8 WAA), respectively.

Broadleaf Weed Control and Crop Safety with Premixed Pyrasulfotole and Bromoxynil in Winter Wheat

For more than two decades acetolactate synthase (ALS) inhibiting herbicides have been the major weed control tools in winter wheat which resulted in selection of resistant weeds to those herbicides. Premix of pyrasulfotole & bromoxynil (Huskie?), a relatively new herbicide, was registered for use in wheat in 2008. Pyrasulfotole inhibits 4-hydoxyphenylpyruvate dioxygenase (HPPD) enzyme in susceptible plants and is the first significant new mode of action for use in cereals for more than two decades. Field experiments were conducted from 2007 to 2010 at two locations in Kansas, USA to test the efficacy of pyrasulfotole & bromoxynil for broadleaf weed control and crop safety in winter wheat. Treatments included pyrasulfotole & bromoxynil alone at 253 g·ai·ha-1 and tank mixtures of pyrasulfotole & bromoxynil at 207 g·ai·ha-1 with MCPA at 280 g·ai·ha-1, dicamba at 140 g·ai·ha-1 or metsulfuron-methyl at 4.2 g·ai·ha-1. Herbicides were applied postemergence in fall and spring seasons. Pyrasulfotole & bromoxynil alone or in combination with tank-mix partners, regardless of application time, controlled flixweed, blue mustard, bushy wallflower and field pennycress 98% or more. Henbit control was better when pyrasulfotole & bromoxynil treatments were applied in fall than spring (≥98% vs ≥67%). Pyrasulfotole & bromoxynil alone applied in spring was not effective on wild buckwheat, but tank mixing with dicamba or metsulfuron-methyl controlled it 84% or more. Pyrasulfotole & bromoxynil alone or as tank mixture caused little (≤7%) or no injury to wheat and the injury did not influence wheat grain yields. Based on excellent control of broadleaf weeds evaluated, pyrasulfotole & bromoxynil is an alternative tool to control ALS-inhibitor resistant weeds in winter wheat. Fall season application and tank mixing with other herbicides are desirable for effective and broad spectrum weed control.

Precipitation Influences Pre- and Post-Emergence Herbicide Efficacy in Corn

Selecting a preemergence (PRE) and postemergence (POST) herbicide program that has the greatest efficacy can be difficult for corn producers and is highly dependent on weed spectrum. Weather conditions before and after herbicide application can further complicate decisions because they influence herbicide efficacy. Eleven field trials were conducted at three locations in Southwestern Ontario from 2003 to 2006, to determine the most effective PRE and POST corn herbicides for weed control. The most abundant weed species across all locations were redroot pigweed (Amaranthus retroflexus L.), common ragweed (Ambrosia artemisiifolia L.), common lambsquarters (Chenopodium album L.), and green foxtail (Setaria viridis (L.) Beauv.). Nine PRE herbicide treatments and eleven POST (applied at the 3-4 leaf stage of corn) herbicide treatments were tested. Results from this study suggest that the timing and amount of precipitation influence herbicide efficacy. For example, precipitation levels 0-17 mm within seven days after herbicide application (PRE or POST) provided unacceptable weed control in treatments that included atrazine, dimethenamidp, isoxa-flutole/atrazine or S-metolachlor/benoxacor. Cumulative precipitation during the 14 days after PRE application that exceeded the monthly average (by at least 64%) reduced Setaria viridis control with pendimethalin. This study demonstrates that a better understanding of how environmental conditions, especially precipitation affect herbicide efficacy, need to be considered by growers when selecting a corn herbicide program to reduce the possibility of weed control failure.

Efficacy and Phytotoxicity Trial of Different Dosages of 4% Nicosulfuron SC on Weeds in Corn Fields

[Objective]The paper was to study efficacy and phytotoxicity of different dosages of 4% nicosulfuron on weeds in corn fields.[Method]With summer corn variety Zhengdan 958commonly used in field production in Hengshui area of Hebei Province of China as the test material,different dosages（1 050,1 500 and 1 950mL/hm2）of corn postemergence herbicide 4% nicosulfuron SC were sprayed during five-leaf stage of corn,and the treatments with water spraying and manual weeding were set as controls.The effects of different dosages of 4% nicosulfuron SC on weed control efficacy and safety and yield of corn were analyzed in order to determine the optimal dosage.[Result]Spraying 4% nicosulfuron SC with dosage of 1 500mL/hm2 during five-leaf stage of corn not only had better control effect against various weeds,but also did not produce phytotoxicity on corn,and the yield of corn was higher.[Conclusion]The study provided scientific information for using 4% nicosulfuron to eradicate weeds in corn fields.