João Guilherme Zanetti de Arantes

Interaction between burndown systems and post-emergence weed control affecting soybean development and yield

RESUMO - Este trabalho teve por objetivo avaliar a interacao entre sistemas de manejo e de controle de plantas daninhas em pos-emergencia na cultura da soja, cv. BRS 154, em plantio direto em areas com expressiva cobertura vegetal. Foram avaliados 13 tratamentos, compostos por um esquema fatorial (3x4)+1. Os fatores eram constituidos por tres sistemas de manejo (dessecacao imediatamente antes da semeadura, dessecacao 10 dias antes da semeadura e dessecacao antecipada, sendo esta composta por duas aplicacoes de manejo, a primeira 24 dias antes da semeadura e a segunda na data da semeadura), quatro formas de controle das plantas daninhas apos a emergencia da cultura (nenhum controle, capina manual das parcelas, aplicacao unica e aplicacao sequencial de herbicidas) e um tratamento adicional, constituido por uma testemunha absoluta (sem manejo e sem controle em pos-emergencia). Embora a dessecacao nos diferentes sistemas de manejo tenha sido eficiente, a antecipacao da dessecacao no manejo antecipado favoreceu a emergencia e o desenvolvimento inicial da soja, proporcionando maiores ganhos de produtividade, nas condicoes de infestacao apresentadas. O sistema de manejo afetou tambem o fluxo de emergencia das plantas daninhas apos a emergencia da soja, com menos reinfestacoes no sistema de manejo antecipado, em funcao do controle dos fluxos iniciais proporcionado pela segunda aplicacao deste sistema de manejo. O manejo realizado na data da semeadura e dez dias antes prejudicou o desenvolvimento da soja, resultando em menor produtividade. O manejo antecipado, quando comparado aos demais sistemas, proporcionou maior produtividade da soja. Palavras-chave: aplicacao sequencial, dessecacao, plantio direto.

Sistemas de manejo de plantas daninhas no desenvolvimento e na produtividade da soja

The choice of the adequate moment for the desiccation of the green cover that precedes the sowing is fundamental for the success of no-till soybeans. This context, the work was aimed to study two burndown systems: desiccation immediately before sowing (AP) and anticipated desiccation (MA), composed by two burndown herbicide applications. For MA, the first application of glyphosate (1240 g ha-1) occurred between 30 and 35 days before the sowing of the crop, and the second was done just before sowing. For AP, the applications (1080 to 1260 g ha-1 of glyphosate) occurred within 48 hours prior to sowing. The trials were developed in 2003/2004 growing season, in six localities in Parana State: Sertaozinho, Campo Mourao, Iretama, Pitanga, Boa Esperanca, and Mambore, in areas with high density of weeds preceding no-till soybean sowing. Evaluations related to weed control and soybean development and grain yield were performed. MA burndown systems provided improved control of weeds after crop emergence. Soybean plants from AP areas were shorter, in comparison to ME, evidencing a delay in the shoot growth. Reduction of grain yield was verified for all localities when AP burndown system was adopted, with reductions between 15% and 50%.

Efeito residual de flumioxazin sobre a emergência de plantas daninhas em solos de texturas distintas

This work aimed to evaluate the residual effect of flumioxazin on weed emergence in soils of distinct textures. Treatments were constituted by the combination of four periods of application (14, 10, 7 and 0 days before sowing) with two rates of flumioxazin (25 and 40 g ha-1), and no herbicide application for each weed species in soils with distinct textures. Residual activity of flumioxazin was evaluated by counting the emerged weeds for each species at 35 days after sowing. Control of initial flows of weed emergence varied with soil type, period of time between herbicide application and weed sowing. A. tenella, D. horizontalis, D. insularis, D. tortuosum, E. heterophylla, N. physaloides and S. latifolia, in both soils, were the most susceptible species to flumioxazin, applied at 25 and 40 g ha-1.

Efeito de subdoses de 2,4-D na produtividade do algodão e suscetibilidade da cultura em função de seu estádio de desenvolvimento

__________________________________ 1 T r ab lh op e s nt dfm o IV iW ScC g (D u, A -2 046 ).2 E ngo A ro om ,Pf. dj utD ep a iUv s l M a( ) - R F :(0XX44) 3261. 4407, rsojunior@uem.br, Bolsista CNPq. 3 E ngo A ro om ,M .Sc D ep atd i(U ) a - PR B l s CN q4 G r adu n oemAg i, B l stI cca Cif a e PD h (UEM) .N qRecebido pelo Conselho Editorial em: 3-3-2005 Aprovado pelo Conselho Editorial em: 10-7-2006

Estimativa do período que antecede a interferência de plantas daninhas na cultura da soja, Var. Coodetec 202, por meio de testemunhas duplas

This work aimed to evaluate the period before weed interference in soybeans, var. Coodetec 202, in a no-till area in Maringa, PR, using two-fold checks. The main weed in this area after crop installation was Bidens pilosa, averaging from 50 to70 plants m-2. Other minor weeds were Euphorbia heterophylla, Brachiaria plantaginea, Sida rhombifolia, Acanthospermum hispidum, Commelina benghalensis, Cenchrus echinatus and Desmodium tortuosum. The crop was kept free of weed interference during initial periods after crop emergence (7, 10, 14, 21, 28, 35, 42, 49 days after emergence and for the whole the crop cycle 118 days). After each consortium period, weeds were manually eliminated, as well as the new weeds thereafter, until crop harvest. Two additional standards with pre- and post-emergence herbicide treatments were also evaluated. For weed interference periods e > 14 days, there was a significant soybean yield decrease. Using two-fold checks, it was established that the period before weed interference must be10 days after soybean emergence. Yield losses ranged from 16.8% (weed interference for 14 days after crop emergence) to 28.03% (interference for the entire cycle). Yield loss estimate by delaying weed control up to 18 days after crop emergence (timing for post-emergence control) was 452 kg ha-1 (16,74%).