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RESUMO No Brasil, a buva destaca-se entre as principais plantas daninhas da cultura da soja, devido à sua agressividade e resistência ao glifosato. Dessa forma, para evitar a seleção de populações resistentes ao herbicida glifosato, o uso de outros herbicidas tornou-se fundamental para o manejo dessa planta daninha. Este estudo objetivou avaliar a eficiência de controle dos herbicidas glifosato e saflufenacil em plantas de buva (Conyza bonariensis), bem como o tipo de interação da combinação desses herbicidas no controle de buva resistente a glifosato. O delineamento utilizado foi o de blocos ao acaso, com quatro repetições. Os tratamentos foram compostos por combinações de doses de glifosato (0 g ha-1; 270 g ha-1; 540 g ha-1; 1.080 g ha-1; 2.160 g ha-1; 4.320 g ha-1; 8.640 g ha-1; 17.280 g ha-1) e saflufenacil (0 g ha-1; 0,55 g ha-1; 1,09 g ha-1; 2,18 g ha-1; 4,37 g ha-1; 8,75 g ha-1; 17,5 g ha-1; 35 g ha-1), formando seis curvas de dose-resposta. Houve efeito sinérgico entre os herbicidas glifosato e saflufenacil para o controle de buva resistente ao glifosato, sendo a mistura considerada eficiente para o biótipo estudado. Além disso, a adição de glifosato (540 g ha-1) ao herbicida saflufenacil (35 g ha-1) preveniu a ocorrência de rebrote e a dispersão de novas sementes de buva, o que não ocorre em plantas tratadas apenas com saflufenacil.

BACKGROUND Poly(ϵ‐caprolactone) nanocapsules (NC + ATZ) are an efficient carrier system for atrazine and were developed as an alternative to reduce the harmful environmental effects of this herbicide. Here, we analyzed the pre‐emergence herbicidal activity of NC + ATZ against Bidens pilosa and evaluated its residual effect on soybean plants after different periods of soil treatment with the formulations. RESULTS In contrast to non‐nanoatrazine, NC + ATZ treatment led to very high mortality rates of B. pilosa seedlings even after a tenfold dilution, which suggests that atrazine nanoencapsulation improved its pre‐emergence herbicidal activity. In a short‐term assay (17 days), soil treatment with all atrazine‐containing formulations resulted in intense toxicity to soybean plants. NC + ATZ at 200 g ha−1 had the same inhibitory effects on the physiological and growth parameters of soybean plants compared with non‐nanoatrazine at 2000 g ha−1, which suggests that atrazine nanoencapsulation increased the short‐term residual effect of the herbicide. In a long‐term assay (60 days), a gradual recovery of soybean plants from atrazine phytotoxicity was observed. When comparing the effects of nano‐ and non‐nanoatrazine at the same concentrations, the growth and physiological parameters of soybean plants were mainly affected to the same extent. This indicates that encapsulation of atrazine into poly(ϵ‐caprolactone) nanocapsules did not enhance the long‐term residual effect of the herbicide on soybean. CONCLUSION NC + ATZ could be applied for efficient weed control without additional phytotoxicity to susceptible crops compared with non‐nanoatrazine, provided that a safe interval is respected from atrazine application to sowing. © 2019 Society of Chemical Industry

The understanding of mechanism of herbicide resistance in weeds is essential for adequate or innovative weed management practices. The aim of this study was to identify and analyze the expression of genes related to degradation enhancement of imazethapyr in barnyardgrass (Echinochloa crus-galli L. Beauv.). One susceptible (SUSSP01) and two populations previouslly identified as resistant to imazethapyr (ARRGR01 and PALMS01) were used. Gene expression of CYP and GST, the translation initiating factor eIF4B, and ALS genes were evaluated after imazethapyr spraying. A reference gene stability analysis was carried out, wherein the genes 18S and actin showed to be more stable in response to the population and herbicide treatment. The gene expression analysis was performed by qRT-PCR. There was no difference in the relative expression of the ALS gene. The CYP81A6 and GSTF1 genes showed higher relative expression in the resistant populations. The CYP81A6 gene had expression 9.61 and 8.44 higher in the resistant populations ARRGR01 and PALMS01, respectively, in comparison with the untreated susceptible population. The expression of this gene was induced by spraying the herbicide imazethapyr. The GSTF1 gene showed higher relative expression in PALMS01 population, reaching 12.30 times higher in plants treated with imazethapyr in relation to untreated susceptible population. The expression of eIF4B gene in the resistant populations treated with imazethapyr was about six times higher than observed in susceptible population. The high relative expression of CYP81A6 and GSTF1 genes indicate the importance of degradation enhancement for the resistance of barnyargrass to imazethapyr.

-Herbicides mixtures are used in many situations without the adequate knowledge related with the effect on major target weeds. The objective of this study was to evaluate the effects of different herbicides mixtures used in irrigated rice in order to establish the adequate combinations for the prevention and management of herbicide resistance in barnyardgrass (Echinochloa crus-galli). Three experiments were performed at field conditions with all major post-emergent herbicides used in irrigated rice in Brazil. The first experiment was performed with barnyardgrass resistant to imidazolinone herbicides and herbicides applied at label rates. The second and third experiments were performed with barnyardgrass resistant and susceptible to imidazolinone herbicides applied at doses of 50 or 75% of the label rates. The occurrence of additive, synergistic and antagonistic effects was identified at 18, 18 and 64%, respectively, among the total of 50 different associations of herbicide and rates evaluated. In general, the mixture of ACCase inhibitors with ALS inhibitors, quinclorac, clomazone + propanil or thiobencarb resulted in antagonism. Sinergic mixtures were found in clomazone with propanil + thiobencarb, profoxydim with cyhalofop-butyl or clomazone, and quinclorac with imazapyr + imazapic, bispyribac-sodium or cyhalofop-butyl. The mixtures of quinclorac with profoxydim were antagonic. Rice grain yield varied according to the efficiency of weed control. Seveveral mixtures were effective for imidazolinone resistant barnyardgrass control.