A tolerância da cultura de milho aos herbicidas do grupo das sulfoniluréias, aplicados em condições de pós-emergência é variável em função do híbrido cultivado. Da mesma forma, tem sido observada tolerância diferencial ao nicosulfuron entre as cultivares de arroz melhoradas para tolerar os herbicidas imazethapyr + imazapic (AHAS-tolerante). Desta forma, este trabalho foi desenvolvido com o objetivo de avaliar: a seletividade do herbicida nicosulfuron, aplicado em condições de pós-emergência, a híbridos de milho e cultivares de arroz AHAS-tolerante. No experimento com a cultura do milho, foram estudados dez híbridos designados comercialmente por DKB 370, DKB 990, AG 6020, AG 9040, AS 1551, AS 1572, SWB 585, BX 1149, BM 620 e BM 128, sendo o delineamento experimental adotado em blocos casualizados, com cinco tratamentos e quatro repetições. Os tratamentos utilizados em g i.a. ha-1 foram: nicosulfuron + atrazina a 20 + 1500; nicosulfuron + atrazina a 40 + 3000; nicosulfuron a 50; nicosulfuron a 60, bem como a testemunha capinada, aplicados no estádio fenológico de quatros folhas expandidas (V4). Os híbridos que foram tolerantes a todos os tratamentos, não apresentando reduções de produção, foram DKB 370, AG 9040, AS 1551 e BM 620. Os tratamentos de nicosulfuron em mistura com atrazina nas doses de 20 + 1500 e 40 + 3000 g ha-1 de i.a. foram seletivos para todos os híbridos testados. As doses de nicosulfuron a 50 e 60 g i a ha-1 foram as mais fitotóxicas do experimento, os híbridos DKB 990, AG 6020, AS 1572, SWB 585, BX 1149 e BM 128 apresentaram redução de produção para ambas as dose. Para os híbridos AG 6020 e SWB 585 ocorreu diferenças de producão entre os tratamentos de nicosulfuron a 50 e 60 g i a ha- 1, o que indica suscetibilidade ao nicosulfuron. A tolerância ao nicosulfuron das duas cultivares de arroz AHAS-tolerante IRGA 422 CL e Puitá CL INTA foi testada em um outro experimento. Os tratamentos resultaram de esquema do tipo fatorial 2 x 8, em que duas foram as cultivares de arroz e oito foram as doses de nicosulfuron (0; 6,25; 12,5; 25; 50; 100; 200 e 400 g i.a.ha-1). Foram realizadas avaliações visuais de sintomas de fitotoxicidade aos 15 e 20 dias após a aplicação (DAA) e aos 20 DAA avaliou-se o comprimento de raiz, comprimento da parte aérea das plantas e massa seca de cada cultivar separadamente. Os dados foram submetidos à aplicação do teste F na análise da variância posteriormente a aplicação de regressões não lineares do tipo log-logístico. A cultivar IRGA 422 CL tolerou maiores doses de nicosulfuron quando comparada com a cultivar Puitá CL INTA. / The tolerance of the crop corn to the sulfonylurea herbicides, sprayed in post emergence conditions, is variable according to the hybrids that is cultivated. Likewise, it has been observed differential tolerance to nicosulfuron among rice cultivars bred to tolerate the herbicides imazethapyr + imazapic (AHAS-tolerant). Therefore, this research was developed in order to evaluate the selectivity of the herbicide nicosulfuron, sprayed in post emergence conditions, to corn hybrids and AHAS-tolerant rice cultivars. In the experiment with the crop corn, it was studied ten hybrids commercially designated as DKB 370, DKB 990, AG 6020, AG 9040, AS 1551, AS 1572, SWB 585, BX 1149, BM 620 e BM 128, being the experimental design adopted romdomized completely blocks, with five treatments and four replications. The treatments used in g a.i. ha-1 were: nicosulfuron + atrazine at 20 + 1,500; nicosulfuron + atrazine at 40 + 3,000; nicosulfuron at 50; nicosulfuron at 60, as well as a check weed free, sprayed in the phenological stage of four expanded leaves (V4). The hybrids that were tolerant to all treatments, with no yield reduction, were DKB 370, AG 9040, AS 1551 e BM 620. The treatments of nicosulfuron in mixture with atrazine at the rates of 20 + 1,500 e 40 + 3,000 g ha-1 of i.a. were selective to all hybrids tested. The rates of nicosulfuron at 50 and 60 g a.i. ha-1 were the least selective of the experiment, the hybrids DKB 990, AG 6020, AS 1572, SWB 585, BX 1149 and BM 128 showed yield reduction. For the hybrids AG 6020 and SWB 585 there were diferences in the yield among treatments of nicosulfuron 50 and 60 g a.i. ha-1, indicating low tolerance to nicosulfuron. The tolerance to nicosulfuron of the AHAS-tolerant rice cultivars IRGA 422 CL and Puita CL INTA was tested in another experiment. The treatments were obtained from a factorial design 2 x 8, with two rice cultivars and eight rates of nicosulfuron (0, 6.25, 12.5, 25, 50, 100, 200 and 400 g a.i.ha- 1). Visual observations of phytotoxicity symptoms were evaluated at 15 and 20 days after treatments (DAA) and at 20 DAA it was evaluated the root and shoot length and dry biomass of each cultivar separately. The data were submitted to F test in the analysis of variance followed by the application of non linear regressions log-logistic type. The cultivar IRGA 422 CL tolerated higher rates of nicosulfuron when compared to the cultivar Puita CL Inta.

A tolerância da cultura de milho aos herbicidas do grupo das sulfoniluréias, aplicados em condições de pós-emergência é variável em função do híbrido cultivado. Da mesma forma, tem sido observada tolerância diferencial ao nicosulfuron entre as cultivares de arroz melhoradas para tolerar os herbicidas imazethapyr + imazapic (AHAS-tolerante). Desta forma, este trabalho foi desenvolvido com o objetivo de avaliar: a seletividade do herbicida nicosulfuron, aplicado em condições de pós-emergência, a híbridos de milho e cultivares de arroz AHAS-tolerante. No experimento com a cultura do milho, foram estudados dez híbridos designados comercialmente por DKB 370, DKB 990, AG 6020, AG 9040, AS 1551, AS 1572, SWB 585, BX 1149, BM 620 e BM 128, sendo o delineamento experimental adotado em blocos casualizados, com cinco tratamentos e quatro repetições. Os tratamentos utilizados em g i.a. ha-1 foram: nicosulfuron + atrazina a 20 + 1500; nicosulfuron + atrazina a 40 + 3000; nicosulfuron a 50; nicosulfuron a 60, bem como a testemunha capinada, aplicados no estádio fenológico de quatros folhas expandidas (V4). Os híbridos que foram tolerantes a todos os tratamentos, não apresentando reduções de produção, foram DKB 370, AG 9040, AS 1551 e BM 620. Os tratamentos de nicosulfuron em mistura com atrazina nas doses de 20 + 1500 e 40 + 3000 g ha-1 de i.a. foram seletivos para todos os híbridos testados. As doses de nicosulfuron a 50 e 60 g i a ha-1 foram as mais fitotóxicas do experimento, os híbridos DKB 990, AG 6020, AS 1572, SWB 585, BX 1149 e BM 128 apresentaram redução de produção para ambas as dose. Para os híbridos AG 6020 e SWB 585 ocorreu diferenças de producão entre os tratamentos de nicosulfuron a 50 e 60 g i a ha- 1, o que indica suscetibilidade ao nicosulfuron. A tolerância ao nicosulfuron das duas cultivares de arroz AHAS-tolerante IRGA 422 CL e Puitá CL INTA foi testada em um outro experimento. Os tratamentos resultaram de esquema do tipo fatorial 2 x 8, em que duas foram as cultivares de arroz e oito foram as doses de nicosulfuron (0; 6,25; 12,5; 25; 50; 100; 200 e 400 g i.a.ha-1). Foram realizadas avaliações visuais de sintomas de fitotoxicidade aos 15 e 20 dias após a aplicação (DAA) e aos 20 DAA avaliou-se o comprimento de raiz, comprimento da parte aérea das plantas e massa seca de cada cultivar separadamente. Os dados foram submetidos à aplicação do teste F na análise da variância posteriormente a aplicação de regressões não lineares do tipo log-logístico. A cultivar IRGA 422 CL tolerou maiores doses de nicosulfuron quando comparada com a cultivar Puitá CL INTA. / The tolerance of the crop corn to the sulfonylurea herbicides, sprayed in post emergence conditions, is variable according to the hybrids that is cultivated. Likewise, it has been observed differential tolerance to nicosulfuron among rice cultivars bred to tolerate the herbicides imazethapyr + imazapic (AHAS-tolerant). Therefore, this research was developed in order to evaluate the selectivity of the herbicide nicosulfuron, sprayed in post emergence conditions, to corn hybrids and AHAS-tolerant rice cultivars. In the experiment with the crop corn, it was studied ten hybrids commercially designated as DKB 370, DKB 990, AG 6020, AG 9040, AS 1551, AS 1572, SWB 585, BX 1149, BM 620 e BM 128, being the experimental design adopted romdomized completely blocks, with five treatments and four replications. The treatments used in g a.i. ha-1 were: nicosulfuron + atrazine at 20 + 1,500; nicosulfuron + atrazine at 40 + 3,000; nicosulfuron at 50; nicosulfuron at 60, as well as a check weed free, sprayed in the phenological stage of four expanded leaves (V4). The hybrids that were tolerant to all treatments, with no yield reduction, were DKB 370, AG 9040, AS 1551 e BM 620. The treatments of nicosulfuron in mixture with atrazine at the rates of 20 + 1,500 e 40 + 3,000 g ha-1 of i.a. were selective to all hybrids tested. The rates of nicosulfuron at 50 and 60 g a.i. ha-1 were the least selective of the experiment, the hybrids DKB 990, AG 6020, AS 1572, SWB 585, BX 1149 and BM 128 showed yield reduction. For the hybrids AG 6020 and SWB 585 there were diferences in the yield among treatments of nicosulfuron 50 and 60 g a.i. ha-1, indicating low tolerance to nicosulfuron. The tolerance to nicosulfuron of the AHAS-tolerant rice cultivars IRGA 422 CL and Puita CL INTA was tested in another experiment. The treatments were obtained from a factorial design 2 x 8, with two rice cultivars and eight rates of nicosulfuron (0, 6.25, 12.5, 25, 50, 100, 200 and 400 g a.i.ha- 1). Visual observations of phytotoxicity symptoms were evaluated at 15 and 20 days after treatments (DAA) and at 20 DAA it was evaluated the root and shoot length and dry biomass of each cultivar separately. The data were submitted to F test in the analysis of variance followed by the application of non linear regressions log-logistic type. The cultivar IRGA 422 CL tolerated higher rates of nicosulfuron when compared to the cultivar Puita CL Inta.

Giant ragweed is an extremely competitive weed and poor control in soybean could lead to significant yield losses for Ontario producers. In 2008, a giant ragweed biotype near Windsor, ON was not controlled with glyphosate and further testing confirmed it as the first glyphosate-resistant (GR) weed in Canada. Giant ragweed seed was collected from 102 locations in Essex (70), Kent (21), Lambton (10) and Waterloo (1) counties to document the occurrence and distribution of GR giant ragweed in Ontario. Giant ragweed seedlings were sprayed with glyphosate at 1800 g a.e. ha-1, and evaluated 1, 7, 14 and 28 days after application (DAA). Results from the survey concluded that there are 47 additional locations in southwestern Ontario with GR giant ragweed. The majority of the sites were found in Essex county, but there was one location in both Chatham-Kent and Lambton counties. Field trials were established at six sites with GR giant ragweed during the 2010 and 2011 growing seasons. The objectives were to determine the level of giant ragweed control with increasing doses of glyphosate, and glyphosate tank mixes applied either preplant or postemergence. Control of giant ragweed increased with higher doses of glyphosate, but only at doses that are not economical for producers. The most effective glyphosate tank mixes were 2, 4-D ester, saflufenacil, linuron, and cloransulam-methyl providing up to 98, 94, 99 and 97% control 4 weeks after application (WAA), respectively. Glyphosate plus dicamba in dicamba-tolerant soybean provided up to 100% giant ragweed control, 4 WAA at the three confined field trial locations. / Monsanto Canada Inc.; Canadian Agricultural Adaptation Program; Grain Farmers of Ontario

Herbicides have become a key component in modern agricultural production. Meanwhile, there is a concern that some herbicides persist past the growing season of the treated crop, and negatively influence the production of the subsequently planted crops. Amongst various herbicides used in western Canada, acetohydroxyacid synthase (AHAS)-inhibiting herbicides warrant special attention given their residual properties and acute plant toxicity at low concentrations in soil. Soil residual AHAS inhibitors have the potential to influence both leguminous host plants and their bacterial symbiotic partners; consequently, the use of an AHAS inhibitor in a given year can negatively influence the inoculation success and grain yield of legumes cropped in the following year. <p>The present thesis project focused on one of the AHAS inhibiting herbicides (flucarbazone) and studied its potential for carryover injury and negative influence on the success of inoculation in field pea. A series of growth chamber and field experiments were conducted to test the following null hypothesis: the presence of residual flucarbazone in soil does not affect nodulation of field pea by inoculum rhizobia. <p>A growth chamber experiment clearly demonstrated the susceptibility of field pea to the presence of flucarbazone in soil where the lowest concentration of flucarbazone amendment (5 ìg kg1) significantly reduced the crop growth. In contrast, a field study failed to reveal any negative effects of flucarbazone use on crop growth and N2 fixation. <p>It was concluded that if the weather and soil conditions favour decomposition of flucarbazone as described in the present study, flucarbazone applied at the recommended field rate will not persist into the following season at high enough concentrations to negatively influence field pea growth, grain yields, and inoculation success. To ensure safety of rotational crops, it is important to strictly adhere to the herbicide application guidelines. Additionally, producers are cautioned to be particularly aware of the environmental and soil conditions that may reduce the rate of herbicide degradation.

Herbicides have become a key component in modern agricultural production. Meanwhile, there is a concern that some herbicides persist past the growing season of the treated crop, and negatively influence the production of the subsequently planted crops. Amongst various herbicides used in western Canada, acetohydroxyacid synthase (AHAS)-inhibiting herbicides warrant special attention given their residual properties and acute plant toxicity at low concentrations in soil. Soil residual AHAS inhibitors have the potential to influence both leguminous host plants and their bacterial symbiotic partners; consequently, the use of an AHAS inhibitor in a given year can negatively influence the inoculation success and grain yield of legumes cropped in the following year. <p>The present thesis project focused on one of the AHAS inhibiting herbicides (flucarbazone) and studied its potential for carryover injury and negative influence on the success of inoculation in field pea. A series of growth chamber and field experiments were conducted to test the following null hypothesis: the presence of residual flucarbazone in soil does not affect nodulation of field pea by inoculum rhizobia. <p>A growth chamber experiment clearly demonstrated the susceptibility of field pea to the presence of flucarbazone in soil where the lowest concentration of flucarbazone amendment (5 ìg kg1) significantly reduced the crop growth. In contrast, a field study failed to reveal any negative effects of flucarbazone use on crop growth and N2 fixation. <p>It was concluded that if the weather and soil conditions favour decomposition of flucarbazone as described in the present study, flucarbazone applied at the recommended field rate will not persist into the following season at high enough concentrations to negatively influence field pea growth, grain yields, and inoculation success. To ensure safety of rotational crops, it is important to strictly adhere to the herbicide application guidelines. Additionally, producers are cautioned to be particularly aware of the environmental and soil conditions that may reduce the rate of herbicide degradation.