Herbicides in the initial growth and chlorophyll indices of sugarcane in pre-sprouted seedlings.

The aim of the present study was to assess the selectivity of herbicides applied in the pre and post-planting of pre-sprouted seedlings (PSS). The experiment was conducted in a greenhouse, using a completely randomized design, with nine treatments and four repetitions. The IACSP95-5000 cultivar was used. The treatments consisted of herbicides applied in five doses as follows: in pre-planting: sulfentrazone, diclosulam, imazapic, and imazapyr, in post-planting: ethoxysulfuron, halosulfuron, 2,4-D and MSMA, and a control treatment without herbicide. Injury symptoms were assessed at 7, 15, 30, 45, 60, 75, and 90 days after application (DAA), height, diameter, number of tillers, chlorophyll A, B, and total chlorophyll at 30, 60, and 90 DAA, leaf area, shoot and root dry mass at 90 DAA. The post-emergent herbicides were considered selective. Pre-planting herbicides reduced the variables assessed at 90 DAA, observed by linear regression for diclosulam and imazapic, and exponential regression for imazapyr. Treatments with sulfentrazone caused few injury symptoms, with subsequent recovery. In addition, all the variables analyzed were equal to control, with the sulfentrazone considered selective for the IACSP95-5000 cultivar.

Glyphosate-resistant hairy fleabane (Conyza bonariensis) exhibits a larger number of trichomes and altered stomatal density relative to the susceptible counterpart

Following the adoption of Roundup Ready crops, glyphosate spraying frequency increased, while the use of other herbicide modes of action was neglected. Herbicide-resistant biotypes were reported in three major Conyza species in Brazil, including Conyza bonariensis, increasing growers' bottom line. Considering that leaf surface structures affect proper herbicide deposition, uptake, and performance, this study aimed to characterize epicuticular surface components in glyphosate-resistant (R) and -susceptible (S) C. bonariensis. Conyza spp. seeds were collected in 36 locations in Brazil, and plants were subjected to resistance screening tests by spraying glyphosate at 720 and 1440 g ae ha-1 (0.5X and 1X the label recommended rate, respectively). For resistance level characterization, C. bonariensis biotypes with contrasting responses were selected for glyphosate dose-response assays. Leaf tissues for epicuticular surface analysis were harvested from newly-obtained R and S biotypes at two growth stages. Histological cuts were made on a leaf area of 25 mm² with a blade. Samples were fixed in Karnowsky solution, gradually changed to 100% ethanol, critical-point dried with CO2, and coated with gold, followed by stomatal and trichome density quantification using scanning electron microscopy. Results indicated a poor control with glyphosate in 33 of 36 Conyza spp. biotypes, and a high (31.5) resistance factor was calculated after dose-response trials. Leaf surface analysis indicated that C. bonariensis leaves are amphistomatic and exhibit tectorial trichomes. A higher number of trichomes and altered stomatal density (number.mm²) were quantified in R compared to the S counterpart, potentially reducing glyphosate uptake and effectiveness.

Efficacy of the herbicides indaziflam and clomazone on problematic weeds of family poaceae to sugarcane crop

It is believed that indaziflam gives a longer period of weed control compared to clomazone, irrespective of the type or texture of the soil. Thus, the aim of this study was to evaluate pre-emergent control in five problematic weed species of family Poaceae to sugarcane, using the herbicides indaziflam and clomazone in two soils of different textures. Two experiments were carried out, one in a soil of a sandy-loam texture and the other in a clayey soil. For both experiments, a randomised block design of split plots was chosen, with four replications. The treatments consisted of the herbicides indaziflam (75 and 100 g ai ha-1), clomazone (1080 g ai ha-1) and a control with no herbicide. In the subplots, the treatments were Digitaria horizontalis, Panicum maximum, Rottboellia cochinchinensis, Urochloa decumbens and Urochloa plantaginea. Both herbicides were more effective in the clayey soil, but with indaziflam (100 g ai ha-1), more than 90% control of the weeds remained after 240 days after application (DAA), whereas for clomazone, control remained only up to 90 DAA. The herbicide clomazone did not satisfactorily control the weeds in the sandy-loam soil. The herbicide indaziflam did not control U. decumbens in the sandy-loam soil. D. horizontalis and R. cochinchinensis were the most sensitive species to the herbicide indaziflam, irrespective of soil texture.

Chemical management of Cyperus rotundus L. and other weeds at sugarcane in PSS system

Among the main weeds with difficult to control in the sugarcane fields can be cited purple nutsedge (Cyperus rotundus L.). This specie was observed in the seed bank in sugarcane fields harvested with or without burning. The objective of this study was to evaluate the efficacy of herbicides in pre-sprouted seedlings (PSS) of sugarcane in the control of C. rotundus and other weeds. The work was carried out in the field, in a randomized complete block design, and four replications. The treatments corresponded to the herbicides applied in pre-planting: sulfentrazone (800 g a.i. ha-1), diclosulam (193.17 g a.i. ha-1), imazapic (133 g a.i. ha-1) and imazapyr (500 g a.e. ha-1); post-planting: halosulfuron (112.5 g a.i. ha-1), ethoxysulfuron (135 g a.i. ha-1), MSMA (1,975 g a.i. ha-1) and 2,4-D (1,340 g a.e. ha-1); besides a control treatment weeding and another without weeding. The symptoms of injury on sugarcane plants, percentage of weed control, variables related to agronomic performance of sugarcane, and yield were evaluated. The herbicides diclosulam, imazapic, and imazapyr caused serious damage to the crop. The halosulfuron, ethoxysulfuron, MSMA, and 2,4-D did not cause symptoms of injury to sugarcane, however, the treatments had a reduced yield due to the low weed control. The sulfentrazone treatment obtained the second highest yield but with effective weed control (>70%) up to 45 days after planting. The best controls were obtained with pre-planting treatments; however, herbicide positioning studies should be performed in relation to PSS.

Herbicide management in glyphosate and sulfonylurea-tolerant soybeans / Manejo de herbicidas em soja tolerante a glifosato e sulfonilureias

There is little information on the efficacy and selectivity of sulfonylureas, isolated and in association with glyphosate, in glyphosate and sulfonylurea-tolerant soybeans. Thus, the present study aims to evaluate the efficacy of weed control and selectivity of sulfonylureas, isolated and in association with glyphosate, at post-emergence (V4) of RR2/STS soybean. The experiments were conducted in the in areas located in Piracicaba City, São Paulo State (SP), Brazil (experiment I) and Palotina City, Paraná State (PR), Brazil (experiment II). Treatments were composed of application of the herbicides sulfometuron, chlorimuron, halosulfuron, ethoxysulfuron and glyphosate, isolated and in association, in the BMX Garra RR2/STS cultivar. Experiment I was conducted focusing on the evaluation of the efficacy of weed control; whereas experiment II focused mainly on the evaluation of herbicide selectivity. The experimental design was the randomized complete block, with four replications. Crop injury, weed control, and variables related to agronomic performance were evaluated. Data were submitted to analysis of variance, and the means of the treatments were compared with the Tukey test. Sulfonylureas in association with glyphosate were effective in weed control and selective for the BMX Garra RR2/STS soybean cultivar. The sulfometuron + chlorimuron + glyphosate association presented phytotoxic potential for the BMX Garra RR2/STS cultivar.(AU)

Há poucas informações sobre a eficácia e seletividade de sulfonilureias, isoladas e associadas ao glifosato, na soja tolerante ao glifosato e às sulfonilureias. Assim, o presente estudo teve como objetivo avaliar a eficácia no controle de plantas daninhas e seletividade de sulfonilureias, isoladas e em associação com o glifosato, em pós-emergência (V4) de soja RR2/STS. Os experimentos foram conduzidos em áreas localizadas nos municípios de Piracicaba, São Paulo (SP), Brasil (experimento I) e Palotina, Paraná (PR), Brasil (experimento II). Os tratamentos foram compostos pela aplicação dos herbicidas sulfometurom, clorimurom, halossulfurom, etoxissulfurom e glifosato, isolados e em associação, no cultivar BMX Garra RR2/STS. O experimento I foi realizado com o foco principal na avaliação da eficácia no controle de plantas daninhas; ao passo que o experimento II se concentrou principalmente na avaliação da seletividade dos herbicidas. O delineamento experimental foi o de blocos casualizados, com quatro repetições. Foram avaliados sintomas de injúria, controle de plantas daninhas e variáveis relacionadas ao desempenho agronômico. Os dados foram submetidos à análise de variância, e as médias dos tratamentos foram comparadas pelo teste de Tukey. Sulfonilureias associadas ao glifosato foram eficazes no controle de plantas daninhas e seletivas para o cultivar de soja BMX Garra RR2/STS. A associação sulfometurom + clorimurom + glifosato apresentou potencial fitotóxico para o cultivar BMX Garra RR2/STS.(AU)