Search Results (5)

Studies exploring the competitive interactions between common beans and weeds are essential to adopt more efficient management strategies in the field, thereby reducing production costs. This study aimed to evaluate the competitive ability of bean cultivars in the presence of sourgrass (Digitaria insularis), using different plant proportions in associations. The experiments were conducted in a greenhouse, arranged in a randomized block design with four replications, from October 2020 to February 2021. Treatments were organized in the following plant proportions of beans and sourgrass: 100:0, 75:25, 50:50, 25:75, and 0:100%. The competitiveness analysis was carried out using replacement series diagrams and relative competitiveness indices. At 50 days after emergence (DAE), measurements were taken for leaf area, plant height, gas exchange, shoot dry mass, and nutrient concentration in bean leaves. The results show that interference between common bean cultivars and sourgrass involves equivalent competition mechanisms. Increasing sourgrass density negatively affects physiological traits and gas exchange in beans by about 10%. Beans show about 15% higher relative growth than sourgrass, based on competitiveness indices. Nutrient levels vary by cultivar and competitor ratio. Intercropping harms species more than intraspecific competition. Further field studies should determine critical control stages and economic impacts, aiding weed management decisions in bean production. Full article

Anthracocystis panici-leucophaei, causal agent of smut on Digitaria insularis (sourgrass), was evaluated as a biological control agent for this weed. Two types of inocula (teliospore and sporidia) were tested to assess its infectivity. The effects of teliospore and sporidia inoculations at different phenological stages of sourgrass were compared, as well as the potential of sporidia and teliospores in post-emergence sourgrass management. Virulence tests were conducted with the isolates obtained from D. insularis and evaluation of specificity of A. panici-leucophaei. Both teliospores and sporidia of A. panici-leucophaei are infective to D. insularis in three different phenological stages. Newly emerged plants with one pair of leaves are more sensitive to A. panici-leucophaei. Infection by A. panici-leucophaei inhibits the growth of sourgrass, decreasing several physiological parameters of D. insularis plants. The fungus produces systematic infection of sourgrass plants and may induce the formation of sori in a significant proportion of the plant panicles, partly castrating those plants. Among sixteen A. panici-peucophaei isolates tested, isolate 46 was the most virulent and inhibited the growth of sourgrass plants, and thus appears to have good potential as a biological control agent to be deployed against sourgrass. A. panici-leucophaei was demonstrated to be specific to D. insularis. Full article

Brazil stands out in the world for being one of the largest producers and consumers of common beans and cowpeas. However, the cultivation of this agricultural species is exposed to competition with weeds for water, light and nutrients. One of the management methods for weed control is the use of pre-emergent herbicides. Although pre-emergence herbicides are beneficial in controlling weeds, it is important to know the dynamics of these products in the soil, especially their residual effect. Two experiments were carried out to assess the tolerance of bean genotypes to the pre-emergent herbicide S-metolachlor in two Brazilian soils. Bean genotypes have differential tolerance to S-metolachlor when grown in soils with different characteristics. The Vigna spp. were the most affected by S-metolachlor, especially the red Adzuki. Plant growth was more sensitive when grown in sandy soil for most species. Total chlorophyll content was not affected for most genotypes in the two soils evaluated. The differential tolerance of the genotypes in both soils confirms the potential of S-metolachlor to cause damage to the bean crop, especially in sandy soil. The S-metolachlor was efficient in controlling sourgrass and selective to the bean cultivars (Pérola and Talismã) in both soils evaluated. Alexandergrass behaved differently in the soils evaluated, showing tolerance to the application of S-metolachlor when in Oxisol and sensitivity in Ultisol. Full article

Glyphosate is the most widely used herbicide for weed control in citrus orchards in Brazil; therefore, it is likely that several species have gained resistance to this herbicide and that more than one resistant species can be found in the same orchard. The objective was to identify weeds resistant to glyphosate in citrus orchards from different regions of the São Paulo State (SP) and determine how many resistant species are present within the same orchard. Seeds of Amaranthus deflexus, A. hybridus, Bidens pilosa, Chloris elata, Conyza bonariensis, Digitaria insularis, Solanum Americanum, and Tridax procumbens, which, as reported by growers, are suspected to be resistant to glyphosate, were collected from plants that survived the last application of this herbicide (>720 g of acid equivalent [ae] ha^–1) in sweet orange and Tahiti acid lime orchards. Based on dose–response and shikimic acid accumulation assays, all populations of A. deflexus, A. hybridus, B. pilosa, and T. procumbens were sensitive to glyphosate. However, populations of B. pilosa from the Olimpia region (R-NS, R-PT and R-OdA) showed signs of resistance based on plant mortality rates by 50% within a population (LD₅₀ = 355–460 g ae ha⁻¹). All populations of C. bonariensis, C. elata, and D. insularis were resistant to glyphosate, presenting resistance ratios from 1.9 to 27.6 and low shikimate accumulation rates. Solanum americanum also showed resistance, with resistance ratios ranging from 4.3 to 25.4. Most of the citrus orchards sampled presented the occurrence of more than one species resistant to glyphosate: Nossa Senhora—one species; Olhos D’agua and Passatempo—two species; Araras—four species; and Cordeiropolis and Mogi-Mirim—up to five species. The results reported in this paper provide evidence of multiple species in citrus orchards from São Paulo that have exhibited resistance to glyphosate. This underscores the difficulties in managing glyphosate-resistant weeds which are prevalent throughout the country, such as C. bonariensis and D. insularis. The presence of these resistant species further complicates the control of susceptible species that may also develop resistance. In addition, the glyphosate resistance of S. americanum was identified for the first time. Full article

Weeds pose a problem, infesting areas and imposing competition and harvesting difficulties in agricultural systems. Studies that provide the use of alternative methods for weed control, in order to minimize negative impacts on the environment, have intensified. Native flora represents a source of unexplored metabolites with multiple applications, such as bioherbicides. Therefore, we aimed to carry out a preliminary phytochemical analysis of crude extracts and fractions of Miconia auricoma and M. ligustroides and to evaluate these and the isolated metabolites phytotoxicity on the growth of the target species. The growth bioassays were conducted with Petri dishes with lettuce, morning glory, and sourgrass seeds incubated in germination chambers. Phytochemical analysis revealed the presence of flavonoids, isolated myricetin, and a mixture of quercetin and myricetin. The results showed that seedling growth was affected in a dose-dependent manner, with the root most affected and the seedlings of the lettuce, morning glory, and sourgrass as the most sensitive species, respectively. Chloroform fractions and myricetin were the most inhibitory bioassays evaluated. The seedlings showed structural changes, such as yellowing, nonexpanded cotyledons, and less branched roots. These results indicate the phytotoxic potential of Miconia allelochemicals, since there was the appearance of abnormal seedlings and growth reduction. Full article