Effects of irrigated rice sowing season and imazapyr + imazapic time of application on rice grain yield and red rice management

Irrigated rice sowing season and red rice competition are among the main factors affecting grain yield. The objective of this work was to evaluate the sowing date of irrigated rice and moments of application of the herbicide imazapyr + imazapic to control red rice management and irrigated rice grain yield. Eight experiments were performed at the following dates (09/30, 10/19, 11/08 and 12/01) for the 2010/2011 harvest season and (09/27, 10/17, 11/08 and 12/05) for the 2011/2012 harvest season. The treatments were: application of the herbicide imazapyr + imazapic at doses of 105+35 g ha-1 in pre-emergence (PRE); 52.5+17.5 g ha‑1 in pre-emergence and 52.5+17.5 g ha-1 in post-emergence (PRE + POST); and 105+35 g ha-1 in post- emergence (POST), and a control without application and no weeding. The cultivar Puitá Inta CL was used and a randomized block design with four replicates. A joint analysis of the experiments was carried out. There was less emergence of red rice and higher grain yield of the irrigated rice at the early periods (09/30/10 and 09/27/11), with 10,578 and 8,653 kg ha-1, respectively. At the end of the season (12/01/10 and 12/05/11), there was greater reduction of the red rice seed bank. Sowing at the beginning of the recommended period provided more irrigated rice grain yield. The application of imazapyr + imazapic at a dose of 52.5+17.5 g ha-1 in PRE + 52.5+17.5 g ha-1 POST, and 105+35 g ha-1 only in PRE and POST was effective in the control of red rice. A época de semeadura de arroz irrigado e a competição com arroz-vermelho estão entre os principais fatores que alteram o rendimento de grãos da cultura. O objetivo deste estudo foi avaliar épocas de semeadura do arroz irrigado e dos momentos de aplicação do herbicida imazapyr+imazapic no controle de arroz-vermelho e no rendimento de grãos de arroz irrigado. Realizaram-se oito experimentos nas seguintes épocas: (30/09, 19/10, 08/11 e 01/12) safra 2010/11 e (27/09, 17/10, 08/11 e 05/12) safra 2011/12. Os tratamentos avaliados foram: aplicação do herbicida imazapyr+imazapic nas doses de 105+35 g ha-1 em pré-emergência (PRE); 52,5+17,5 g ha-1 em pré-emergência e 52,5+17,5 g ha-1 em pós-emergência (PRE+POS); e 105+35 g ha-1 em pós-emergência (POS), além de uma testemunha sem aplicação e sem capina. O cultivar utilizado foi Puitá Inta CL, e o delineamento utilizado foi blocos ao acaso em quatro repetições. Realizou-se análise conjunta dos experimentos em cada safra. Ocorreu menor emergência de arr