André Andres

Herbicides are commonly used for weed control in wheat production due to their effectiveness, speed, and lower cost compared to other management methods. This study aimed to evaluate the selectivity and efficacy of herbicides applied alone or in combination for controlling major weed species infesting wheat in Brazil. Field experiments were conducted in 2022 and 2023 using a randomized complete block design with four replications. Terbuthylazine (500 and 750 g ha ⁻¹ ) + adjuvant, carfentrazone-ethyl (120 g ha ⁻¹ ), saflufenacil and pyraflufen-ethyl (3.75 and 5 g ha ⁻¹ ) + clodinafop-propargyl caused the highest phytotoxicity to wheat. The best wheat physiological performance (internal CO ₂ concentration, photosynthesis and transpiration rates, stomatal conductance, water use, and carboxylation efficiencies) was observed with terbuthylazine (750 g ha ⁻¹ ), carfentrazone-ethyl (80 g ha ⁻¹ ), 2,4-D (670 g ha ⁻¹ ), and terbuthylazine + clodinafop-propargyl (750 + 96 g ha ⁻¹ ). Terbuthylazine (500 and 750 g ha ⁻¹ ) and pyraflufen-ethyl (3.75 and 5 g ha ⁻¹ ) combined with clodinafop-propargyl (96 g ha ⁻¹ ), provided the most effective control of wild radish and ryegrass and resulted in the highest grain yields. Regarding the grain yield components of wheat (number of plants per meter, number of spikes, spike length, number of filled and sterile grains, hectoliter weight, thousand-grain mass, and grain yield), the weed-free control and the treatment with terbuthylazine + clodinafop-propargyl (750 + 96 g ha⁻¹) showed the best performance. In the absence of weed control, average grain yield losses reached 91%. The herbicides terbuthylazine and pyraflufen-ethyl demonstrated potential for the control of broadleaf weeds such as wild radish, which exhibit resistance to acetolactate synthase inhibitors, and where 2,4-D is less effective under low-temperature conditions. However, further studies using commercial formulations, adjuvants, and varietal tolerance tests are required to validate the use of these herbicides on wheat in Brazil.

Background: Ryegrass is considered an important weed in crops in the state of Rio Grande do Sul, Brazil, for being resistant to the herbicide glyphosate. Objective: This study evaluates ryegrass control by applying different spray volumes and doses of clethodim alone or in combination with glyphosate and/or 2,4-D. Methods: Two field experiments were conducted in a 5 x 3 factorial design. In experiment I, factor A consisted of clethodim (96 g a.i. ha-1); clethodim (96 g a.i. ha-1) + [...] Background: Ryegrass is considered an important weed in crops in the state of Rio Grande do Sul, Brazil, for being resistant to the herbicide glyphosate. Objective: This study evaluates ryegrass control by applying different spray volumes and doses of clethodim alone or in combination with glyphosate and/or 2,4-D. Methods: Two field experiments were conducted in a 5 x 3 factorial design. In experiment I, factor A consisted of clethodim (96 g a.i. ha-1); clethodim (96 g a.i. ha-1) +

- The objective of this work was to evaluate the ecophysiological aspects of seed germination in California arrowhead (Sagittaria montevidensis) biotypes resistant and susceptible to herbicides. The experimental design was completely randomized. In paddy rice fields, seeds were collected from two biotypes that are resistant (SAGMO 10 and SAGMO 32) and from one that is susceptible (SAGMO 35) to acetolactate synthase and photosystem II inhibiting herbicides. Seed dormancy release was performed with 2.0% potassium nitrate, chemical (1.0% H2SO4 for 30 s) and mechanical (sandpaper) scarification, 10 ppm gibberellic acid, water imbibition for 24 hours, water bath at 60°C, and a control. Germination was evaluated at temperatures from 10 to 40°C and seedling emergence at 0.0, 0.5, 1.0, 2.0, 4.0, and 5.0 cm burial depths. All biotypes showed a germination higher than 70% after mechanical scarification. The highest germination rate occurs at 25.9°C for SAGMO 35, the susceptible biotype, and at 26.2 and 26.5°C, respectively, for SAGMO 10 and SAGMO 32, the resistant biotypes. For all biotypes, the highest seedling emergence occurs in seeds positioned at the 0.5 and 1.0 cm burial depths.

Among the weeds that interfere with the growth and development of sweet sorghum, beggar ticks stands out, because it has a high competitive capacity for the available resources. This study aims to compare the competitive ability of sweet sorghum (Sorghum bicolor (L.) Moench) against hairy beggarticks (Bidens pilosa L.), as a function of cultivar and plant proportion. Experiments were conducted in a greenhouse in a completely randomized design with four replications and six treatments. Treatments were arranged in replacement series in the proportions of 100:0, 75:25, 50:50, 25:75, and 0:100% (sorghum:weed) equivalent to 20:0, 15:5, 10:10, 5:15 and 0:20 plants per pot with 8 dm3 capacity of sweet sorghum (cultivars ‘BRS 506’, ‘BRS 509’ or ‘BRS 511’) against hairy beggarticks. Fifty days after emergence, plant leaf area (LA), aboveground dry mass (DM), photosynthesis (A), and transpiration rates (E) were measured. Competitive ability was analyzed by using the graphical analysis method and building diagrams based on total and relative productivity. Competitiveness, clustering coefficient, and aggressiveness were also determined. Sorghum cultivars, in general, showed losses independently of the proportion of hairy beggarticks. Statistical analysis showed small differences in competitive ability among sorghum cultivars; ‘BRS 509’ was also demonstrated to be slightly more competitive than ‘BRS 506’ and ‘BRS 511’ against hairy beggarticks. This, however, is unlikely to provide a competitive advantage for ‘BRS 509’ in production fields, and hairy beggarticks should be efficiently controlled early in the crop cycle to avoid productivity losses, independently of the sorghum cultivar.

Florpyrauxifen-benzyl (FPB) is a new class of auxinic herbicide developed for selective weed control in rice. This study aimed to evaluate the effect of environmental conditions, P450 inhibitors, rice cultivar response, and gene expression on FPB selectivity in rice. Field experiments established in a randomized block design showed that rice plant injury due to two FPB rates (30 and 60 g ai ha⁻¹) was affected by planting time and rice stage at herbicide application. The injury was higher at the earliest planting season and more in younger plants (V₂) than larger (V₆ and R₀). However, no yield reduction was detected. Under greenhouse conditions, two dose-response experiments in a randomized block design showed that spraying malathion (1 kg ha⁻¹) before FPB application did not reduce herbicide selectivity. The addition of two P450 inhibitors (dietholate and piperonyl butoxide, 10 g a.i. seed-kg⁻¹ and 4.2 kg ai ha⁻¹, respectively) decreased the doses to cause 50% of plant injury (ED₅₀) and growth reduction (GR₅₀). However, it seems not to compromise crop selectivity. BRS Pampeira cultivar showed lower ED₅₀ and GR₅₀ than IRGA 424 RI. A growth chamber experiment was conducted in a completely randomized design to evaluate the gene expression of rice plants sprayed with FPB (30 and 60 g ai ha⁻¹). Results showed downregulation of OsWAKL21.2, an esterase probably related to bio-activation of FPB-ester. However, no effect was detected on CYP71A21 monooxygenase and OsGSTL transferase, enzymes probably related to FPB degradation. Further research should focus on understanding FBP bio-activation as the selective mechanism.

Background Weeds compete with crops, demanding efficient control to avoid yield losses. Highly competitive cultivars are a cultural method that can increase weed suppression and reduce the effects of crop-weed competition. Objective The present study aimed to assess the competitive abilities of barley cultivars (crop) against black oat (weed) and their interference in crop physiology. Methods A preliminary additive experiment was carried out with increasing densities of barley and black oat to determine the minimal density from where there [...] Abstract Background Weeds compete with crops, demanding efficient control to avoid yield losses. Highly competitive cultivars are a cultural method that can increase weed suppression and reduce the effects of crop-weed competition. Objective The present study aimed to assess the competitive abilities of barley cultivars (crop) against black oat (weed) and their interference in crop physiology. Methods A preliminary additive experiment was carried out with increasing densities of barley and black oat to determine the minimal density from where there

Clearfield™ (CL) rice (Oryza sativa L.) is a weedy rice (Oryza spp.; synonym = red rice) control tool that has been used in Brazil since 2003. This system includes the use of an imidazolinone (IMI)-tolerant cultivar and the application of IMI herbicides. In this review article, Brazilian weed scientists evaluate the challenges and lessons learned over 18 yr of CL use. CL system benefits include selective weedy rice control, better crop establishment during the most advantageous period of the year, and more efficient fertilizer use. In Rio Grande do Sul state, the CL system, in conjunction with other improvements, has contributed to rice grain yield gains from 5,500 kg ha⁻¹ before 2002 to around 8,400 kg ha⁻¹ currently. In contrast, the main problem that has arisen over this period is the rapid evolution of IMI-resistant weedy rice, caused by gene flow from CL rice cultivars. The off-label use (rate and continuous use) of IMI herbicides has contributed to the evolution of resistance in Echinochloa spp. and other weeds. IMI herbicide carryover has also affected susceptible crops grown after CL rice. Crop rotation with soybean [Glycine max (L.) Merr.] is increasing, ensuring system sustainability. The importance of minimum tillage has also become apparent. Such cultivation includes applying nonselective herbicides before sowing or just before crop emergence (at the spiking stage to eliminate as much weedy rice as possible and other weeds at an early growth stage). It also includes the use of certified seeds free of weedy rice, following label instructions for IMI herbicides, applying the herbicide PRE followed by POST, and complementary weedy rice management practices, such as roguing of surviving weedy rice plants.

The abundance of weedy rice (Oryza sativa L.) in the soil seedbank was estimated in 2011 in Italian rice (Oryza sativa L.) fields with different histories of IMI-resistant Clearfield® rice varieties (CL), non-Clearfield® varieties (NCL) and planting methods. A model was used to predict weedy rice seedbank dynamics over time under different control strategies. Soil samples were taken from 50 rice fields cultivated with CL varieties consecutively for 0, 1, 2, or 3 years and weedy rice seedbank data were used in a model considering eight scenarios: A) rice monoculture with CL and NCL varieties in alternate years; B) two years of CL, followed by one year with NCL; C) three years of CL followed by one year of NCL; D) rice monoculture with only CL; E) rice monoculture with only NCL; F) two years of CL followed by one year of rotation with another crop (CR), and then by an additional year with NCL; G) one year of CR followed by two years of CL, and then by one year of NCL; H) two years of CR followed by two years of CL. Weedy rice seedbank exceeded 1,000 seeds m−2 in the surveyed fields with no significant differences between rice planting methods. Highest densities were found in fields cultivated for one year with CL varieties. Simulations indicated that where CL varieties were used in rice monoculture susceptible weedy rice seedbank reduced gradually, allowing a depletion after 17, 13, 11, and 9 years in scenarios A), B), C), and D), respectively. The weedy rice seedbank increased in NCL monoculture (E) and declined significantly in crop rotation scenarios (F, G, H). The simulations indicated that the introduction of crop rotation is crucial for obtaining a relatively fast reduction of weedy rice seedbank and delaying the evolution of herbicide-resistant populations.