Do Crop Rotations in Rice Reduce Weed and Echinochloa spp. Infestations? Recommendations for Integrated Weed Control

Abstract

The species belonging to the genus Echinochloa represent the main weeds in rice fields worldwide. Heavy soils are especially appropriate for this crop that is often grown in monoculture. A drought period in 2012 impeded farmers from sowing rice in some parts of the region of Aragon (northeastern Spain) and, unusually, they seeded alternative crops such as winter cereal, fescue (Festuca arundinacea), ryegrass (Lolium multiflorum) and lucerne (Medicago sativa). A total of 20 fields were selected, in which rice had been grown in monocrop until 2011 and several crop sequences were established afterwards; weed vegetation was recorded in spring, summer and autumn 2014-16 to find out if the crop rotations reduced weed infestations. Winter cereal and fescue were the crops with the highest soil cover; ryegrass and lucerne had difficulties in installation probably due to the heavy soil textures. Echinochloa spp. plants were found in the winter cereal stubble after having grown fescue for the previous two years and rice before that; in the forage fields, small plants of earing Echinochloa spp. adapted to mowing were detected. Recommendations for Integrated Weed Management that arise from the observations are ploughing the winter cereal stubble before seed shed of the emerged Echinochloa plants, assuring a high density of the forage crops, and efficient herbicide control in rice fields.