Naiara Guerra

Winter and summer management strategies for Conyza bonariensis and Bidens pilosa control.

Conyza bonariensis is one of the most important weeds in southern Brazil. The selection of biotypes tolerant and resistant to the herbicide glyphosate has led to increasing demand for alternatives of management strategy to control this species. This work aimed to evaluate the efficiency of different winter and summer management strategy for the control of Conyza bonariensis, by using glyphosate + 2,4-D tank mixtures combined or not with residual herbicides. The different burndown alternatives were applied after corn harvest (winter burndown), associated to applications before soybean sowing (summer burndown) with a total of 15 treatments. Winter burndown options evaluated in this research were efficient in weed desiccation and provided excellent levels of residual weed control up to the next summer soybean pre-sowing. The sowing of oats after winter burndown with subsequent summer burndown with glyphosate+diclosulam + 2,4-D was found to be efficient to control Bidens pilosa. Conyza bonariensis was totally controlled in all the burndown strategies in which the herbicide 2,4-D was associated to glyphosate.

Misturas em tanque com glyphosate para o controle de trapoeraba, erva-de-touro e capim-carrapicho em soja RR ®

Although the use of glyphosate tank mixtures for managing weed species of difficult control is prohibited by theBrazilian legislation, it has been a common practice among farmers. This work aimed to evaluate the efficiency andselectivity of herbicide tank mixtures using glyphosate to control Commelina benghalensis L., Tridax pr ocumbens L.and Cenchr us echinatus L. in soybean crop RR

Tolerance of grain sorghum to 2,4-D applied in post-emergence.

Grain sorghum is one of the major species cultivated as a winter crop in savannah areas in Brazil. Although 2,4-D is currently used on this crop, little has been done to understand crop susceptibility as a function of its vegetative stage at spraying. The present work was carried out to determine the selectivity of 2,4-D applied in post-emergence on grain sorghum. The cultivar AG-1040 was grown in 10 dm-3 pots under greenhouse conditions. The experiment was set up in a completely randomized design, in a factorial scheme 5 x 3, composed by five rates of 2,4-D (0, 210; 420; 840 and 1.608 g ha-1), applied at three phenological stages: three, five and nine completely expanded leaves. Visual crop injuries were more intense when the herbicide was applied at the earlier stages of sorghum development. However, the main negative effects related to plant productivity and lodging were observed in herbicide applications carried out at later stages of crop development.

Levantamento fitossociológico de plantas daninhas em cafezal orgânico

A adequacao de um cafezal para o sistema orgânico causa grande mudanca no sistema de manejo de plantas daninhas, mas as informacoes sobre o comportamento da comunidade infestante em areas de cultivo de cafe orgânico sao escassas no Brasil. Objetivou-se com este trabalho realizar um levantamento fitossociologico da comunidade infestante em tres cafezais (variedades Mundo Novo, Bourbon Vermelho e Obata) desenvolvidos em sistema orgânico, no municipio de Garca (SP). Nas tres areas estudadas foram arremessados ao acaso cem quadrados metalicos com area vazada de 0,25 m2, nas entrelinhas da cultura. As especies contidas no interior dos quadros foram identificadas segundo a especie botânica, nome popular e familia. A partir dos resultados, determinaram-se os parâmetros fitossociologicos: frequencia, densidade, abundância, frequencia relativa, densidade relativa, abundância relativa, indice de valor de importância e similaridade floristicas pelos metodos de Simple Matching de Sneath & Sokal e similaridade de Sorensen. As familias que mais se destacaram, com maior numero de especies nas tres areas foram Poaceae e Asteraceae. Houve alta similaridade em todos os contrastes testados, ja que pelo menos metade das especies identificadas foi comum as duas areas contrastadas.

Seletividade do herbicida fomesafen isolado ou em associação com diuron, trifluralin e prometryn para cultivares de algodoeiro

The objective of this work was to evaluate the selectivity of fomesafen, in single application or in association with other herbicides, in pre-emergence of six cotton cultivars. Six experiments were conducted simultaneously in greenhouse conditions, in Red Oxisoil in water with pH of 5,9; 2,94% of OM and 320g kg-1 of clay. The experimental design was completely randomized with five replicates. Treatments were arranged in a factorial scheme (2 x 4) + 1, represented by two doses of fomesafen (375 and 500 g ha-1 - active ingredient) and association with diuron (1,25 kg ha-1 a.i.), trifluralin (1,80 kg ha-1 a.i.) and prometryn (1,25 kg ha-1 a.i.). A herbicide-free treatment was also added. At 30 days after the application of treatments, the cotton shoot was collected to quantify the dry mass accumulation. It was observed that the single fomesafen application or its association with diuron, trifluralin and prometryn affected the dry mass accumulation of the six cultivars. In general, the association of fomesafen with trifluralin was the most selective treatment. There is a differential response of cotton cultivars to fomesafen. The cultivar IMA CD 6001 LL was the most tolerant and IMA 8221 was the most sensible to fomesafen and its associations.