Jamil Constantin

Volunteer soybean is the main weed competing with second-crop maize in Brazil, and options for early control are still limited. Two field trials were carried out in Mandaguaçu (PR) in 2023: one evaluating maize selectivity and another assessing volunteer soybean control. In the selectivity trial, only ametryn and amicarbazone were not selective, reducing maize yield. In the control trial, no treatment achieved 100% control, but amicarbazone (140 and 280 g a.i. ha⁻¹), tembotrione (201.6), terbuthylazine (2800), tembotrione + atrazine (100.8 + 1500) and mesotrione + terbuthylazine (192 + 900) provided efficient control (≥80%) up to 28 DAA. Treatments offering at least 55% early control also resulted in yields similar to the weeded control. Integrating both trials, the best overall results were obtained with atrazine (2500, 5000), mesotrione (192), mesotrione + atrazine (100 + 1000), mesotrione + terbuthylazine (192 + 900), tembotrione, tembotrione + atrazine, terbuthylazine and terbuthylazine + s-metolachlor.

A bioguided identification of the phytotoxic compounds of the Brachiaria ruziziensis L. on the weed species Euphorbia heterophylla L. was conducted. From the butanolic fraction of B. ruziziensis it was separated an active subfraction (Subfraction III) that was demonstrated to contain the steroidal saponins. These substances were determined as protodioscin and protonedioscin by 1H and 13C NMR analysis. b-ethyl glucose was also identified, but it represented only 2.4% of the subfraction III. The effects of pure protodioscin were very similar to those caused by Fraction III or saponins isolated from B. ruziziensis. Root length was the most sensitive variable and the germination indices were little modified. The calculated ID50 for primary root inhibition was 390.1 ± 112.7 µg/ml and 359.5 ± 44.6 µg/ml for saponins and pure protodioscin, respectively. b-ethyl glucose did not cause significant modifications in the germination and seedling growth when assayed at a concentration range of 100 to 1000 µg/ml. These results suggest that protodioscin isomers are the causative compounds of the inhibitory effects on growth of E. heterophylla. These compounds are possibly involved in the reported ability of B. ruziziensis in reducing the emergence and the growth of weed species when used as a cover plants. This finding confirms the potential of the utilization of B. ruziziensis for weed management options in the field.

O capim-pé-de-galinha (Eleusine indica) é uma planta que vem causando muitos problemas no Brasil, principalmente pela dificuldade de controle químico nas áreas de produção de grãos. O objetivo deste trabalho foi investigar a possível ocorrência de resistência cruzada a herbicidas inibidores da ACCase (enzima acetil-CoA carboxilase) numa população proveniente de Paranacity (PR). Os herbicidas avaliados foram fluazifop-p-butyl; quizalofop-p-ethyl, haloxyfop-p-methyl, sethoxydim e clethodim. Foram construídas curvas de dose-resposta em casa de vegetação em experimentos com delineamentos inteiramente casualizados em esquema fatorial 9x2 com quatro repetições. Os níveis do primeiro fator correspondem às doses de cada herbicida e os níveis do segundo fator referem-se aos biótipos susceptível e suspeito de resistência. As doses selecionadas corresponderam a: 0; 1/16; 1/8; 1/4; 1/2; 1; 2; 4; e 8 vezes a dose de bula de cada herbicida e todos os herbicidas foram aplicados em plantas no estádio de um perfilho. Os resultados mostraram que o biótipo proveniente de Paranacity foi suscetível ao clethodim e ao quizalofop-p-ethyl, mas apresentou dificuldade de controle com a utilização de fluazifop-p-butyl, haloxyfop-p-methyl e sethoxydim. O fator de resistência para estes herbicidas foi determinado em 10,66; 5,64; e 9,80 respectivamente. O biótipo de Eleusine indica proveniente de Paranacity foi caracterizado como resistente a fluazifop-p-butyl, haloxyfop-p-methyl e sethoxydim, constituindo o primeiro caso de resistência cruzada aos inibidores da ACCase no estado do Paraná.

Objetivo: Foi avaliar a possibilidade de ocorrência de resistência ao imazethapyr em população de Amaranthus hybridus proveniente da localidade de São Paulo. Referencial teórico: As plantas do gênero Amaranthus spp. são originárias da América e apresentam uma diversidade de espécies. Atualmente 515 casos de plantas daninhas resistentes a herbicidas no mundo. Dentre estas espécies, as plantas do gênero Amaranthus vêm mostrando um aumento de casos de resistência nos últimos anos, o que gera preocupação quanto ao seu manejo químico, existindo seis casos de resistência registrados para essa espécie no Brasil. Método: O delineamento experimental foi inteiramente casualizado em esquema fatorial 2x9, com seis repetições. O primeiro fator foi constituído por duas populações de A. hybridus, sendo, uma com suspeita de resistência ao herbicida imazethapyr, oriunda de Cândido Mota e uma população suscetível de Florínea. As aplicações foram realizadas quando as plantas apresentavam de 4 a 6 folhas. As avaliações realizadas foram a percentagem de controle e a matéria seca. Resultados e conclusão: Foi confirmada a suspeita de resistência das populações de Amaranthus hybridus ao imazethapyr na cidade de Cândido Mota. Implicações da pesquisa: As principais contribuições do estudo são no sentido de demonstrar a existência de um novo problema de resistência nas áreas agricultáveis do Brasil, o que demandara novas alternativas de controle. Originalidade/valor: Este estudo teve como objetivo investigar a possível ocorrência de resistência ao herbicida imazethapyr em Amaranthus hybridus, o que constituirá no primeiro relato desse tipo no Brasil.

The evolution of herbicide-resistant weeds is the major challenge for chemical management worldwide, increasing production costs, and reducing yield. This work aimed to evaluate the putative resistance of the Amaranthus hybridus population from Candido Mota (CMT) to glyphosate and imazethapyr and to investigate the non-target site mechanisms involved. Dose–response studies were conducted under greenhouse conditions and the control and biomass reduction were evaluated 28 days after application (DAA). Absorption, translocation, and metabolization studies were evaluated at 72 h after treatment (HAT) using radiometric techniques. The dose–response results show different responses among populations to glyphosate and imazethapyr. The CMT population was not controlled with labeled herbicide doses. Based on biomass reduction, the resistance factor was 16.4 and 9.4 to glyphosate and imazethapyr, respectively. The CMT absorbed 66% of ¹⁴C-glyphosate and 23% of ¹⁴C-imazethapyr at 72 HAT. Although the CMT population absorbed more glyphosate than the susceptible population (12.6%), translocation was impaired for both herbicides in the CMT when compared to the SUS population. There was no evidence that herbicide metabolization was involved in CMT resistance to the herbicides studied. Understanding the mechanisms endowing resistance allows better decision-making. This is the first study that describes non-target-site resistance mechanisms in an Amaranthus hybridus population from Brazil.

The knowledge of the adequate period for the beginning of weed management in lettuce crop can increase the efficiency of production, reducing the costs with management. The aim of this study was to determine the pre-interference period (PIP), the critical time for weed removal (CTWR) and the critical period of weed control (CPWC) in three lettuce cultivars, Elisa, Lucy Brown and Solaris. Coexistence and the absence of weeds were evaluated for each cultivar. The design was in randomized blocks with seven treatments (0, 7, 14, 21, 28, 35 and 42 days after transplanting - DAT) of coexistence and the same seven periods of weed absence with four replicates in each experiment. The highest infestation densities were with the species Oxalis latifolia, Coronopus didymus and Amaranthus hybridus. The leaf area and number of leaves per plant were reduced by up to 50% and 66%, respectively, in relation to the longest period of coexistence with weeds and yield reduced by 48% (Elisa), 40% (Lucy Brown) and 33% (Solaris). The cultivar Solaris showed greater tolerance to weed interference. Based on yield, PIP was 1, 3 and 3 DAT and CTWR was 37, 37 and 35 DAT, and CPWC was 2 to 37, 3 to 37 and 3 to 35 for the cultivars Elisa, Lucy Brown and Solaris, respectively.

Due to the low availability of herbicide active ingredients, the chemical weed management in lettuce crop is a challenge. The aim of this study was to evaluate the sensitivity of lettuce to the pre-planting application of the herbicides flumioxazin and trifluralin alone or in tank-mixture in lettuce, Lucy Brown cultivar. Two experiments were conducted. In experiment A, the soil was tilled before the herbicide application and it was tilled again before seedling transplanting. In experiment B, the soil was tilled just once before the herbicide application. The experimental design was in randomized blocks in a factorial scheme (3x3) +1 (2 factors with 3 levels and an additional control) with 4 replicates. We applied flumioxazin (120 g ha-1), trifluralin (450 g ha-1) and flumioxazin + trifluralin (120 + 450 g ha-1) in three different seasons before transplanting (0, 7 and 14 days). Lettuce productivity after trifluralin application (48.4 t ha-1) was higher than after flumioxazin application (16.8 t ha-1) in experiment A. In experiment B, flumioxazin decreased the number of lettuce leaves (25.6) at 14 DAT; no differences in lettuce productivity were verified, though. The herbicide trifluralin caused lower levels of phytotoxicity and was the most selective between the treatments when applied in the three seasons in both experiments.

Sugarcane cultivation areas are usually characterized by low soil fertility and high nutrient demand, especially for nitrogen. Technologies that can raise crop yield and lower the use of pesticides and fertilizers are among the main needs of this crop. The objective of this study was to evaluate the agronomic performance of sugarcane after in-furrow application of the diazotrophic bacterium Nitrospirillum amazonense (BR11145). The treatments consisted of applying five doses of N. amazonense-based product to the planting furrow, 0.25, 0.5, 1.0, 1.5, and 2.0 L commercial product (c.p.) ha-1; a treatment consisting of the combination of Bacillus subtilis and Bacillus licheniformis; one control without fertilization; and one control with fertilization. Based on the results obtained from the pooled analysis of two field experiments, the N. amazonense-based product improved the growth parameters of sugarcane plants, and at doses of 1.0 and 1.5 L c.p. ha-1, these benefits resulted in a significant increase in yield and in the amount of sugar per hectare. Inoculation with diazotrophic bacteria can benefit sugarcane, especially because it promotes the growth and yield of the crop similarly to fertilizers.