Knowledge on weed biology and ecology is fundamental to provide suitable control practices in weed management systems. The objective of this research was to understand the effect of light and temperature on germination of Chamaesyce hirta, as well as to evaluate the effect of depth of seed placement in the soil in the emergence of the plant. Two experiments were conducted. In the first one, in the laboratory, the seeds were placed to germinate in plastic boxes and kept in a B.O.D. germination chamber, under constant temperatures of 20, 25, 30 and 35 ºC, either in the dark or under continuous light. Daily germination assessments were performed. The percentage of germinated seeds in the 10-day period and the germination speed index (GSI) were calculated. In the second trial, carried out in greenhouse conditions, 100 seeds were planted, under six levels of seeding depth (0, 1, 2, 3, 4 and 5 cm) and three soil cover conditions: no straw, under black oats (Avena strigosa) straw and under corn (Zea mays) straw. Daily plant emergence was counted along 30 days and total emergence and GSI were calculated. Germination of C. hirta seeds occurs both in the presence and absence of light. For the highest temperature, both increased germination and GSI were reported in the presence of light. The highest levels of emergence were obtained with the absence of plant cover and under corn straw at 0 cm depth. The presence of black oat straw on the soil reduced the emergence of C. hirta.

Amaranthus hybridus is a C4 broadleaf species widely spread across Brazilian agricultural territory. Recently, several herbicide resistance reports have been documented in southern Brazil, including the reports for enolpyruvilshikymate-3-phosphate (EPSPS)-and acetolactate-synthase (ALS)-inhibitors. The objective of this study was to confirm the existence of an ALS resistant (R) A. hybridus population from Paraná state. Dose-response experiments were conducted with R and a known susceptible (S) population with herbicides from three different chemical groups of ALS inhibitors. Biomass relative to untreated control was quantified and GR 50 (dose for 50% of biomass reduction), GR 90 (dose for 90% of biomass reduction) and resistant index (RI) were calculated based on non-linear regression analysis. The R population was 6.9-fold resistant to chlorimuron-ethyl and 6.5-fold resistant to metsulfuron-ethyl (sulfonylureas -SUL). Additionally, the recommended rates from each herbicide was not sufficient to reach 90% control to R based on GR 90 parameter estimation. There was no resistance to imazethapyr (imidazolinone -IMI) and cloransulan-methyl (triazolopyrimidine -TRI) due to the low doses of GR 90 and non-significant RIs. The R A. hybridus population investigated was resistant to ALS inhibitors chlorimuron-ethyl and metsulfuron-ethyl (SUL), but susceptible to IMI and TRI herbicides.

interesse: Os autores declaram não haver conflito de interesses em relação à publicação deste manuscrito.

Sweet sorghum (Sorghum bicolor (L.) Moench) is an interesting alternativefor biomass and ethanol production, however, so far there is very limited knowledge regarding selective herbicide options for weed control in this crop. The objective of this study was to evaluate the selectivity of preemergence herbicides for sweet sorghum. This research was composed by two steps: in the first one, a greenhouse screening was carried out with several herbicide treatments and in the following step the most selective treatments were evaluated on field conditions. In sandy clay loam texture soil, the treatments involving atrazine (1000 and 2000 g ha-1), amicarbazone (210 g ha-1), trifluralin (500 g ha-1) and flumioxazin (25 g ha-1) provided the greatest levels of selectivity to sweet sorghum. In clay soil (64.7% clay), the treatments with atrazine (1000, 1500 and 2000 g ha-1), amicarbazone (280 g ha-1), S-metolachlor (480 g ha-1), [atrazine + S-metolachlor] ([601+471,2 g ha-1), pendimethalin (500 g ha-1) and imazethapyr (42.4 and 63.6 g ha-1) provided the lowest levels of crop injury, and were considered as the most selective for sweet sorghum. Herbicide treatments applied to sandy clay loam soil provided more injuries to sweet sorghum than those applied to clay soil.

A resistência de plantas daninhas a herbicidas demanda novas estratégias de manejo químico da comunidade intraespecífica, visto sua capacidade de interferência em sistemas de cultivo. Objetivou-se avaliar a eficácia de inibidores da ACCase aplicados em mistura ou sequencial com o herbicida 2,4-D, como alternativas de controle de capim-amargoso. O delineamento experimental foi em blocos casualizados, com onze tratamentos e quatro repetições, entre 2015 e 2016. Os manejos foram compostos pelos herbicidas cletodim, haloxifope-p-metílico, fenoxaprope-p-etílico, quizalofope-p-etílico e fluazifope-p-butílico em mistura ou sequencial com 2,4-D, além de aplicações de paraquate e dos graminicidas associados ao glyphosate em todos os tratamentos. Foram realizadas avaliações visuais de controle aos 5 dias antes da semeadura (DAS), e com 0; 10; 20; 40; 50 e 65 dias depois da semeadura (DDS) para determinar o controle de capim-amargoso. A aplicação dos herbicidas cletodim e haloxifope-p-metílico em mistura ou sequencial com 2,4-D não diferem no controle das plantas de capim-amargoso. A aplicação dos herbicidas fenoxaprope-p-etílico, quizalofope-p-etílico e fluazifope-p-butílico em sequencial com o herbicida 2,4-D apresentaram maior controle quando comparada com a aplicação dos mesmos em mistura com 2,4-D. O herbicida fluazifope-p-butílico em mistura com 2,4-D não é indicado para o controle de capim-amargoso.