Barnyardgrass control with pre-emergent herbicides in no-till irrigated rice

Resumo

The adoption of no-till drilled rice by some producers, facilitated by increasing crop rotations and integration with cattle breading, has led to varying ryegrass residue volumes. Herbicide efficiency may vary accordingly to their physicochemical characteristics, interaction with pasture residue, moisture and rainfall availability. Our aim was to investigate the influence of ryegrass residue volume on barnyardgrass control in irrigated rice established in no-till drilling systems. The experiment was conducted during the 2018/19 and 2019/20 crop seasons using a factorial scheme within a randomized block design and four replicates. Factor A was determined by the ryegrass residue volumes, and Factor B was defined by the spraying of pre-emergent herbicides. Barnyardgrass control varied depending on residue volume and soil moisture post-herbicide spraying. Pendimethalin provided poor weed control under conditions of lower post-spraying moisture and higher ryegrass residue volume but resulted in higher panicle density at the end of the cycle. In contrast, the performance of clomazone, [imazapic + imazapyr] and penoxsulam was less affected by these factors. Herbicide efficacy indirectly influenced grain yield, as it was higher in rainy years with greater ryegrass residue volume. Due to its high lipophilicity, pendimethalin's performance was compromised with higher residue volume and low rainfall and should be avoided under these conditions. Clomazone, penoxsulam and [imazapyr + imazapic] were more consistent regardless of residue volume and rainfall.