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The development of glufosinate-resistant corn represents a new weed management system for corn growers. Field experiments were conducted from 1995 to 1997 at four locations in southwestern Ontario. The objective of this study was to determine the effect of timing of weed control relative to the growth stage of corn with glufosinate applied alone or in combination with residual herbicides. Control of all species tested improved with the addition of atrazine plus dicamba to glufosinate, applied from the two- to eight-leaf stage of corn growth. Based on a 90% weed dry matter reduction, glufosinate with atrazine plus dicamba controlled common ragweed, common lambsquarters, and pigweed species at the three-leaf stage of corn and yellow foxtail, barnyardgrass, and large crabgrass at the two-, four-, and eight-leaf stage of corn, respectively. Weed control with glufosinate alone was improved when applied at the later growth stages of corn. Glufosinate applied alone at the four-leaf stage of corn contro...

Eleven sweet corn cultivars were evaluated to identify cultivar sensitivity to nicosulfuron in three field studies, conducted over a 2-yr period. Response to nicosulfuron varied, depending on cultivar and application dose. DelMonte 2038 was highly sensitive to nicosulfuron, resulting in very severe injury and in most cases the death of all plants at both locations each year. At Exeter in 1997 and 1998, injury was slight, with no yield reductions on other cultivars. At Simcoe in 1998, five cultivars showed severe visual injury, especially at 50 g ha−1 of nicosulfuron; however, this did not always result in a significant yield reduction. Cultivars with a yield reduction were Elite, GH 1703 and Calico Belle. The cultivars Bonus Bt, Reveille, Krispy-King, GSS 7831 and GH 2690 were classified as fully tolerant to field applications of nicosulfuron showing injury of 5% or less at 25 g ha−1 and with no yield reduction. Key words: Sensitivity, herbicide injury, cultivars, nicosulfuron, Zea mays

Field experiments were conducted in 1996 and 1997 at five locations in southwestern Ontario to develop dose-response curves for SAN 1269H (SAN 835H plus dicamba) for weed control and crop tolerance in corn. SAN 1269H controlled wild buckwheat (Polygonum convolvulusL.), common ragweed (Ambrosia artemisiifoliaL.), common lambsquarters (Chenopodium albumL.), pigweeds (Amaranthus retroflexusL. andA. powelliiS. Wats.), barnyardgrass [Echinochloa crus-galli(L.) Beauv.], and yellow foxtail [Setaria glauca(L.) Beauv.]. Biologically effective doses of SAN 1269H (BAS 662H) were 440, 430, 180, and 40 g/ha for yellow foxtail, barnyard grass, wild buckwheat, and common ragweed, respectively. The biologically effective dose (that which provides 90% reduction in weed dry matter) for common lambsquarters was 560 g/ha when SAN 1269H was applied preemergence (PRE) and 110 g/ha when applied postemergence (POST). When applied PRE at a rate of 420 g/ha, pigweed was controlled, whereas only 85 g/ha was required when applied POST. Grain yield increased with dose of SAN 1269H and did not differ with time of application. Temporary crop injury was observed when SAN 1269H was applied at the four- to six-leaf growth stage. Optimum corn yields were achieved with doses of 100 to 250 g/ha.

Saflufenacil is a new herbicide being developed by BASF for pre-emergence application for broadleaved weed control in maize and other crops. Three field studies were conducted in Ontario, Canada over a 2-year period (2006 and 2007) to evaluate the tolerance of spring cereals (barley, oats, and wheat) to pre-emergence and post-emergence applications of saflufenacil at 50 and 100 g ai ha −1 . Saflufenacil pre-emergence caused minimal visible injury (1% or less) at 3, 7, 14 and 28 days after emergence and had no adverse effect on plant height or yield of barley, oats, and wheat. Saflufenacil plus the surfactant Merge (1% v/v) applied post-emergence caused as much as 76, 60, 52 and 35% visible injury in spring cereals at 3, 7, 14 and 28 DAT, respectively. Injury with saflufenacil plus Merge applied post-emergence decreased over time and was generally greater as dose increased. Saflufenacil plus Merge applied post-emergence reduced plant height by as much as 16% and reduced yield of spring barley and wheat by 24 and 13%, respectively, but had no effect on the yield of spring oats. Based on these results, saflufenacil applied pre-emergence at the proposed dose can be safely used in spring planted barley, oats and wheat; however, the post-emergence application of saflufenacil results in unacceptable injury and yield loss. These results are consistent with the proposed pre-emergence use pattern for saflufenacil.

Pyroxasulfone is an experimental herbicide for use in field corn (Zea mays L.) and soybean that may have potential for weed management in sweet corn. Tolerance of eight sweet corn hybrids to pyroxasulfone applied preemergence (PRE) at rates of 0, 209, and 418 g·ha−1 a.i. were studied at two Ontario locations in 2005 and 2006. Pyroxasulfone applied PRE at 209 and 418 g·ha−1 caused minimal (less than 3%) injury in Harvest Gold, GH2041, GH9589, GSS9299, GG214, GG446, GG763, and GG447 sweet corn hybrids at 7, 14, and 28 days after emergence. Pyroxasulfone applied PRE did not reduce plant height, cob size, or yield of any of the sweet corn hybrids tested in this study. Based on these results, pyroxasulfone applied PRE at the rates evaluated can be safely used for weed management in Harvest Gold, GH2041, GH9589, GSS9299, GG214, GG446, GG763, and GG447 sweet corn.

Topramezone is a newly introduced herbicide for use in field corn (Zea mays L.) that may have potential for weed management in sweet corn. Tolerance of eight sweet corn hybrids to topramezone applied postemergence (POST) at 0, 50, 75, 100, 150, and 300 g a.i. ha− 1 were studied at one Ontario location in 2000 and two locations in 2001 and 2002. Topramezone applied POST at 50, 75, 100, and 150 g·ha− 1 did not cause any visual injury in Calico Belle, CNS 710, Delmonte 2038, FTF 222, FTF 246, GH 2684, Reveille, and Rival sweet corn hybrids at 7 days after treatment (DAT) and caused minimal injury (less than 5%) at 300 g·ha− 1 in all hybrids. The initial sensitivity observed in these hybrids was minimal and transient with no effect on visual injury at 14 and 28 DAT. Topramezone applied POST did not reduce plant height, cob size, or marketable yield of the sweet corn hybrids included in this study. Based on these results, topramezone applied POST at the rates evaluated can be safely applied to Calico Belle, CNS 710, Delmonte 2038, FTF 222, FTF 246, GH 2684, Reveille, and Rival sweet corn.

Field studies were conducted in 1996 and 1997 at three locations throughout southern Ontario with the objective of developing dose-response curves of RPA 201772 for weed control and crop tolerance in corn. The biologically effective doses required to control redroot pigweed, velvetleaf, and wild mustard were 100, 90, and 80 g/ha, respectively. Yellow foxtail was controlled with 100 to 120 g/ha, while rates for common lambsquarters varied from 60 to 130 g/ha, depending on the year and location. Wild buckwheat control was poor (> 30%) at all of the doses tested. RPA 201772 did not reduce corn grain yield; however, temporary crop injury was evident on coarse sandy soils.

Combining herbicides and fungicides can improve production efficiency; however, there is little information on the effect of these mixtures on weed control and processing tomato crop response. Six field trials were conducted from 2002 to 2004 in Ontario to study the effect of rimsulfuron and thifensulfuron applied alone or in combination with metribuzin and with or without chlorothalonil or copper fungicides on processing tomato. There was no visual injury or reduction in marketable yield of processing tomato with rimsulfuron or thifensulfuron alone or when tank-mixed with chlorothalonil or copper hydroxide. Rimsulfuron, thifensulfuron, rimsulfuron plus metribuzin, and thifensulfuron plus metribuzin could be tank-mixed with chlorothalonil without a reduction in weed control. However, efficacy of rimsulfuron and thifensulfuron were reduced when tank-mixed with copper hydroxide. The reduction in weed control incited by adding copper hydroxide was overcome with a low rate (150 g·ha–1 a.i.) of metribuzin for thifensulfuron but not rimsulfuron. Application of rimsulfuron and thifensulfuron alone or with low rates of metribuzin and chlorothalonil could provide tomato growers with a single-pass treatment for the control of troublesome weeds and diseases.

Four field trials were conducted over a three-year period (2011–2013) in southwestern Ontario to evaluate the level of weed control provided by various halosulfuron tankmixes applied preplant incorporated (PPI) in white bean. Trifluralin, s-metolachlor, halosulfuron, and imazethapyr applied alone or in combination caused 4% or less visible injury 1 and 4 weeks after emergence (WAE) in white bean. Trifluralin, s-metolachlor, halosulfuron, and imazethapyr applied PPI provided 80–96%, 84–95%, 83–100%, and 75–92% control of redroot pigweed; 19–28%, 30–40%, 97–99%, and 73–84% control of common ragweed; 94–96%, 63–82%, 96–100%, and 96–100% control of common lambsquarters; 14-15%, 12–35%, 100%, and 96–97% control of wild mustard; and 96–97%, 95–97%, 53–56%, and 80–82% control of green foxtail, respectively. The two- and three-way tankmixes of halosulfuron with trifluralin, s-metolachlor, or imazethapyr provided 85–100% control of redroot pigweed, 90–98% control of common ragweed, 97–100% control of common lambsquarters, 100% control of wild mustard, and 93–98% control of green foxtail. Weed density, weed biomass and white bean seed yields reflected the level of visible weed control.

A limited number of preplant (PP) herbicides are available for spring seeded cereals in Ontario. Six field trials were conducted at the Huron Research Station, Exeter, Ontario, over a two-year period (Exeter, 2010 and 2011) to evaluate glyphosate, prosulfuron, and glyphosate plus prosulfuron applied PP for weed management in spring seeded no-till barley, oats, and wheat. There was no injury in barley, oats, and wheat with glyphosate, prosulfuron, and glyphosate plus prosulfuron applied preplant at the rates evaluated at 1, 2, and 4 weeks after crop emergence. Prosulfuron provided 49–99% control of AMBEL, 28% or less control of CONAR, 31–94% control of POLCO, 49–98% control of SINAR, and 46–79% control of SONAR. Prosulfuron in combination with glyphosate provided 73–98% control of AMBEL, less than 43% control of CONAR, 39–94% control of POLCO, 63–98% control of SINAR, and 60–85% control of SONAR. Prosulfuron reduced density of AMBEL 76% and SINAR 93% but had no significant effect on density of CONAR, POLCO, or SONAR. Prosulfuron in combination with glyphosate reduced biomass of AMBEL as much as 96% and SINAR 98% but had no significant effect on biomass of CONAR, POLCO, or SONAR. Yield of barley, oats, and wheat was not affected with glyphosate, prosulfuron, and glyphosate plus prosulfuron at the rates evaluated.

Limited information exists on sweet corn (Zea mays) tolerance to postemergence (POST) applications of thifensulfuron-methyl under Ontario growing conditions. Eight sweet corn hybrids were evaluated for tolerance to thifensulfuron-methyl in four field experiments conducted in 2003 and 2004. Thifensulfuron-methyl was applied POST at 6 and 12 g·ha–1 a.i., the registered and twice the registered rate for use in soybean in Ontario. Sweet corn hybrid responses to thifensulfuron-methyl varied. Delmonte 2038 was the most sensitive to thifensulfuron-methyl and had as much as 92% visual injury, 76% height reduction, and 98% yield reduction compared to the nontreated control. Empire, GH1861, GH2298, and GH2684 hybrids showed visual injury of 53%, 55%, 53%, and 61%, height reduction of 34%, 31%, 32%, and 26% and yield reduction of 77%, 68%, 68%, and 51%, respectively. GG214, GH2547, and GSS9299 sweet corn hybrids were not as sensitive to thifensulfuron-methyl. The initial sensitivity observed in these hybrids was minimal and transient with no effect on yield. Although thifensulfuron-methyl is safe for use on some sweet corn hybrids, it has the potential to cause severe crop injury and yield reduction in other hybrids and therefore it should not be recommended for weed management in sweet corn production in Ontario.

There is little information published on the effect of residues from postemergence (POST) applications of foramsulfuron and preemergence (PRE) applications of isoxaflutole, and isoxaflutole plus atrazine in the year after application on vegetable crops. Three trials were established from 2000 to 2002 in Ontario to determine the effects of residues of foramsulfuron, isoxaflutole, and isoxaflutole plus atrazine on cabbage, processing pea, potato, sugar beet, and tomato 1 year after application. Aside from a reduction in sugar beet plant stand, there were no visual injury symptoms in any crop at 7, 14, and 28 days after emergence (DAE) in any of the herbicide carryover treatments. Isoxaflutole residues reduced shoot dry weight and yield as much as 27% and 28% in cabbage, and 57% and 60% in sugar beets, respectively. The addition of atrazine to isoxaflutole caused further reductions in shoot dry weight and yield of cabbage and sugar beet. Isoxaflutole plus atrazine residues reduced shoot dry weight and yield as much as 42% and 43% in cabbage, and 58% and 82% in sugar beets, respectively. There were no adverse effects on shoot dry weight and yield of processing pea, potato, and tomato from isoxaflutole or isoxaflutole plus atrazine residues in the year following application. Foramsulfuron residues at either rate did not reduce shoot dry weight or yield of any crops 1 year after application. Based on these results, it is recommended that cabbage and sugar beet not be grown in the year following the PRE application of isoxaflutole or isoxaflutole plus atrazine.

Field experiments were conducted during 1981 and 1982 in Ontario, Canada, on the effects of quackgrass [Agropyron repens(L.) Beauv. # AGRRE] interference in soybean [Glycine max(L.) Merr.] and the usefulness of infrared thermometry in predicting critical periods of weed interference. Soybean seed yield, dry weight, number of leaves, height, and number of pods were substantially reduced due to quackgrass interference. High levels of P and K fertility did not overcome the quackgrass interference. Part of the competitive effects of quackgrass was alleviated by irrigation. Infrared thermometry successfully detected the first occurrence of quackgrass-induced stress during the early soybean flowering stage, when the quackgrass was in the four-leaf gtowth stage. This coincided with the onset of the first significant soybean yield loss. No additional soybean yield loss occurred after quackgrass reached the five-leaf growth stage. There was an inverse relation between accumulated stress degree days and soybean yield reductions due to quackgrass interference. The use of the stress degree day concept may be a valuable tool in predicting soybean yield losses due to quackgrass interference.