Práticas culturais associadas ao controle químico de capim-arroz e arroz-vermelho na cultura do arroz irrigado.

Abstract

Barnyardgrass (Echinochloa spp.) and red rice (Oryza sativa) are considered the most important weeds in irrigated rice due to infestation level in cultivated areas, difficulties in control and interference on yield and quality of the final product. Chemical control using herbicides has been the primary method employed to control these species in rice fields. However, due to increasing and widespreading of weed-resistance to herbicides, often the control of these species has been unsatisfactory. In this context, the combination of cultural practices with chemical control becomes crucial for ensuring sustainability of the weed management programs by rationalizing herbicide use, and additionally by reducing environmental pollution. Therefore, the objectives of this work were: (i) evaluate herbicide efficiency on barnyardgrass control in two planting dates of rice under intermittent irrigation (Chapter I), (ii) to determine red rice emergence in response to planting dates and rice irrigation management (Chapter II), (iii) evaluate the sensitivity of the red rice biotypes to glyphosate and glufosinate, and the response of these biotypes to the imidazolinone at different planting dates (Chapter III). Based on the main results it can be concluded that herbicides with residual activity such as clomazone and formulated mixture of imazapyr and imazapic provide effective control (> 95%) of barnyardgrass, in despite of the rice planting date under intermittent irrigation management. Profoxydim and cyhalofop-butyl herbicide efficiency increase at november planting date. The highest weed control levels to tank mixtures of propanil plus clomazone are observed at September planting date. The presence of water layer reduces emergence of red rice, however, some biotypes have the ability to germinate and emerge even at 10-cm water depth. The emergence speed and seedlings number of red rice increase at november and december planting dates. Alternative herbicides such as glyphosate and glufosinate can be used to control red rice biotypes with resistance to imidazolinones. Sensitivity of the susceptible biotypes to imidazolinone is lower at september planting date, however, reistant biotype sensitivity to these herbicides is similar between planting dates evaluated.