Abstract Double rice‐cropping areas in the dry and wet seasons have been increasing in Myanmar, and hybrid rice has been cultivated throughout the country. However, weeds are often not adequately managed. Therefore, the objective of this study was to investigate the effect of weed infestation on rice production of three hybrid varieties (Palethwe 1, Palethwe 3, and Palethwe Basmati) and three inbred varieties (Manaw Thu Kha, Shwe Thwe Yin, and Sin Thwe Latt) in the dry and wet seasons in a lowland rice field. In the dry and wet seasons, 19 ‐ 20 weed species were naturally infested into the fields. Limnocharis flava was the most abundant weed in both seasons. Weed dry weight and rice grain yield showed a negative linear relationship in both seasons. Manaw Thu Kha showed the highest yield loss in the un‐weeded fields in both seasons, while Sin Thwe Latt and Palethwe Basmati showed the lowest yield loss in the dry season and wet season, respectively. Sin Thwe Latt recorded the lowest yield loss of 30.21% on average in both seasons, and the highest yield loss of 60.37% was recorded for Manaw Thu Kha. The average rice grain yield loss of all the varieties in the un‐weeded fields was 64.37 and 33.66% for the dry and wet seasons, respectively. Thus, the yield loss in the dry season was 1.9‐times greater than that in the wet season. The present research suggests that adequate weed management is necessary for rice cultivation, especially in the dry season in Myanmar.
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