Several cases of herbicide resistance in goosegrass have been confirmed worldwide. Reports of control failures after glyphosate application have been observed, especially in the Midwest region of Paraná State. The objective of this study was to evaluate the existence of goosegrass populations resistant to glyphosate. For this, 25 populations collected in two consecutive seasons (2013/2014 and 2014/2015) were sown and grown in greenhouse. Glyphosate dose-response curve experiments were performed using doses of 0, 60, 120, 240, 480, 960, 1,920, 3,840, 7,680 and 15,360 g a.e. ha^-1. The application stages were from two to three tillers (E1) for the populations of 2013/2014 and E1 and five to six tillers (E2) for the populations of 2014/2015. Furthermore, three of the populations supposedly considered resistant in these experiments (populations 7, 19 and 25) have had their F1 submitted to the herbicide dose-response test in order to verify whether the resistance was inheritable. With the results obtained in this study, it was concluded that the populations 19 and 25, from Campo Mourão and Luziânia (Midwest of Paraná) are the first confirmed cases of goosegrass resistant to glyphosate in Brazil (RF = 3.99 to 6.81), following all the criteria for confirmation of new weed resistance cases.

E. indica is one of the most problematic weeds in the world because it is present in almost every continent, and there are reports of multiple resistance to herbicides by some biotypes. The objective of this paper was to analyze the growth, the development and the production of this plant's seeds, in order to generate information about its biology that can be useful for management. The experiment was carried out in a greenhouse from May to September 2015. Sixteen samples were taken during the development cycle of the plant: 3, 10, 17, 24, 31, 38, 45, 52, 59, 66, 73, 80, 87, 94, 101 and 108 days after emergence (DAE). The response variables were based on a leaf area and dry matter of each one of the parts of the plant and the number of seeds produced per plant. At 12 DAE, 80% of the seedlings of E. indica had emerged, and each plant produced more than 120 thousand seeds, closing their cycle at 120 DAE. Between 38 and 43 DAE, the plant had fast emission of new tillers, exponential accumulation of the total dry matter and substantial increase of the absolute growth rate. Due to the data observed here, we concluded that the management of E. indica must be done preferably before 38 DAE due to the exponential growth after this period, preventing the plant from producing seeds and spreading to other places.

Due to the limited availability of selective herbicides to control Sumatran fleabane after soybean emergence, it is essential to develop new options that provide effective control prior to planting. A new herbicide formulation containing diclosulam+halauxifen-methyl was evaluated for effectiveness at two Sumatran fleabane plant heights (5 to 10 cm, and 10 to 50 cm) and for soybean selectivity when applied at 7 or 3 d before planting. Combined results from the two sites showed that diclosulam+halauxifen, applied either alone or in a tank mixture with glyphosate, and the tank mixture of diclosulam+2,4-D amine+glyphosate are effective at all rates tested to control Sumatran fleabane in preplant applications. Crop response was observed with applications 7 days before planting at only one of the sites. A rate-dependent crop response was observed for pre-plant applications performed 3 days before soybean planting. However, crop yield was not significantly affected for either timing across all rates. All rates tested of diclosulam+halauxifen in this study were considered safe to soybean.

Resistance to herbicides is a serious threat to crop production worldwide, especially in agronomic crops and cereals. This research evaluated the possible occurrence of Bidens pilosa resistant to imazethapyr and atrazine in Brazil. The resistant biotype was collected from an area with a history of repeated application of photosystem II (PSII) and ALS inhibitor herbicides. The susceptible biotype was collected from an area with no history of herbicide application. Resistance verification experiments were carried out in the greenhouse. The treatments were arranged in a 3 x 8 factorial scheme, where the first factor was populations [susceptible (S), parent resistant (PR), and resistant F1 (RF1)]; and the second factor was herbicide dose (0, 375, 750, 1500, 3000, 6000, 12000 and 24000 g ha^-1 for atrazine; or 0, 12.5, 25, 50, 100, 200, 400 and 800 g ha^-1 for imazethapyr). The resistance factor to atrazine was 2.83 for PR and 5.55 for RF1. This population was more resistant to imazethapyr (>21-fold) than it was to atrazine. The recommended maximum dose of the herbicides did not control this B. pilosa population adequately. The data support the claim that B. pilosa population from this field in Quarto Centenário, Parana is resistant to two herbicide modes of action - PSII inhibitor (i.e. atrazine) and ALS inhibitor (i.e. imazethapyr). This is the first report of such case for this species, globally. Cross-resistance to other ALS inhibitors and other PS II inhibitors as well as the respective mechanisms of resistance to each herbicide are being investigated.

Plants of the genus Amaranthus are important agricultural weeds that compromise food production worldwide. Several biological characteristics make these plants thrive in the environment and cause significant yield losses in many crops. Among the seven most important Amaranthus species in the Americas, four have populations with resistance to more than one mode of action (A. hybridus, A. palmeri, A. retroflexus, and A. viridis). While multiple herbicide-resistance in Amaranthus species is widespread, chemical control remains as one of the most [...] Plants of the genus Amaranthus are important agricultural weeds that compromise food production worldwide. Several biological characteristics make these plants thrive in the environment and cause significant yield losses in many crops. Among the seven most important Amaranthus species in the Americas, four have populations with resistance to more than one mode of action (A. hybridus, A. palmeri, A. retroflexus, and A. viridis). While multiple herbicide-resistance in Amaranthus species is widespread, chemical control remains as one of the most

Uma das ações indiretas exercidas pelas plantas daninhas na interferência sob espécies cultivadas é o potencial de hospedar agentes causadores de enfermidades. O nematoide das lesões radiculares (Pratylenchus brachyurus) vem causando uma série de danos em diversas culturas no Brasil. Para o manejo deste fitoparasita, o cultivo de diferentes espécies de crotalárias tem sido empregado. O objetivo deste trabalho foi avaliar a hospedabilidade de plantas daninhas para P. brachyurus, bem como o efeito de supressão de diferentes espécies de crotalária. Para isso, foi instalado um experimento em casa de vegetação no delineamento inteiramente casualizado em arranjo fatorial (2x17), com seis repetições. O primeiro fator consistiu na presença ou ausência da inoculação do nematoide. O segundo correspondeu a dezessete espécies vegetais, sendo onze plantas daninhas, quatro crotalárias (C. breviflora, C. juncea, C. ochroleuca e C spectabilis) e duas variedades de soja, as quais serviram como testemunha sendo hospedeiras de P. brachyurus. A inoculação do nematoide das lesões radiculares não influenciou a altura de plantas e massa seca de parte aérea das diferentes espécies avaliadas. Portulaca oleracea, Amaranthus viridis e Sida rhombifolia foram as espécies com maior número de nematoides por sistema radicular, e apenas a S. rhombifolia apresentou comportamento semelhante a testemunha (variedade de soja BMX Potência RR^®). Com relação ao número de nematoides por grama de raiz, os maiores valores foram observados para A. viridis, seguido por P. oleracea. Excluindo-se a C. juncea, todas as demais espécies de crotalária apresentaram-se como boas opções para o manejo em áreas infestadas com P. brachyurus.