No abstract

-The repetitive use of iodosulfuron for the control of weeds in winter cereals in the south of Brazil has favored the emergence of resistant Raphanus sativus biotypes. The objective of this study was to evaluate: the response of Raphanus sativus biotypes susceptible and resistant to different dosages of iodosulfuron; the control of biotypes with alternative registered herbicides for the control of the species in crops of wheat, corn and soybean; and the existence of cross-resistance of the biotypes. Thus, four experiments were done in a greenhouse, with a completely randomized design and four replicates. The experimental units were composed of vases with a volumetric capacity of 0.75 L filled with substrate, containing a plant each. For the dose-response curve, three biotypes (factor A) and nine doses of the iodosulfuron herbicide (factor B) were used. For the alternative control, the recommendation was herbicides in pre or postemergence of the crops, and the crossedresistance was evaluated by using herbicides that inhibit the ALS enzyme of different chemical groups. The analyzed variables were control and shoot dry matter. GR 50 of the susceptible biotype (B 1 ) was 0.11 g a.i. ha -1 , whereas GR 50 of resistant biotypes (B 4 and B 13 ) was 102.9 and 86.8 g a.i. ha -1 of the iodosulfuron herbicide, respectively. The resistant biotypes presented crossed resistance to herbicides that inhibit the ALS enzyme, where the control can be efficient with the use of herbicides with different action mechanisms. Keywords:Raphanus sativus, dose-response, acetolactate synthase, weed. RESUMO -O uso repetido do herbicida iodosulfurom para controle de plantas daninhas em cereais de inverno no Sul do Brasil favoreceu o surgimento de biótipos de Palavras-chave:Raphanus sativus, dose-resposta, acetolactato sintase, planta daninha.

The use of herbicides is important for controlling weeds in crops. However, they can present impacts on soil properties, such as biological properties. In this study, we evaluated the responses of soil microbial biomass and enzymes activity to the application of the herbicides imazethapyr and flumioxazin and their mixture in an experiment under laboratory conditions, using soils with a different history of use. Soil microbial biomass C (MBC) decreased, while microbial biomass N (MBN) was not affected after the application of the herbicides as compared to the control. Soil respiration, respiratory quotient, and dehydrogenase (DHA) activity increased significantly after the application of the herbicides compared to the control. The hydrolysis of fluorescein diacetate (FDA) was not significantly different between the control and the herbicide treatments. The principal response curve showed the largest initial effects for the flumioxazin, followed by imazethapyr and their mixture. Flumioxazin had a different influence on soil respiration and respiratory quotient than imazethapyr and their mixture. Finally, the effects of herbicides on soil microbial biomass and enzymes are short-term as we observed recovery in the biological parameters over time.

The successive use of Roundup Ready crops may difficult the management of volunteer plants originated from seed losses during harvest. In soybean, volunteer corn plants can exhibit higher interference and cause reduce yield depending on their density. The aim of this study was to quantify the economic threshold level (ETL) in soybean as a function of the competition of volunteer corn and to evaluate the chemical control in different phenological stages of development. The ETL and chemical control experiments were conducted in the field, under completely randomized and randomized block designs with one and three replicates, respectively. The variables analyzed were yield and ETL as functions of the competition of different volunteer corn populations (control,

Radish is an important weed that causes yield reduction in winter crops in southern Brazil. The control chemical of radish is an important and essential step to prevent damage on crops. However the intensive use of ALS-inhibitors herbicides favors the selection resistant biotypes. The selection can influence the adaptive traits of biotypes with physiological changes and growth variables and plant reproduction. The objective of the study was compare the fitness costs of susceptible and resistant radish biotypes to ALS-inhibitors herbicides. The experiment was conducted in greenhouse using completely randomized design with five replications. The treatments were arranged in factorial arrangement corresponding to susceptible and resistant biotypes (B1 and B4) and nine sampling times (14, 28, 42, 56, 70, 84, 98, 112 and 126 days after emergency), respectively. The variables evaluated were plant height, shoot dry matter, root dry matter, total dry matter, leaf area, growth rate, relative growth rate, leaf area ratio, number of siliques and seeds produced per plant. The results showed that the resistant biotype (B4) had no fitness costs when compared to the susceptible biotype (B1).