Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) resistance to acetolactate synthase-inhibiting and other herbicides in rice in Turkey

Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) is one of the most yield-limiting weeds in rice in Turkey. Barnyardgrass resistance to common herbicides has been reported worldwide; however, such information is largely lacking in the country. The objective of this study was to determine the resistance spectrum of different barnyardgrass populations to the most commonly-used herbicides in rice in Turkey. The susceptibility of 40 barnyardgrass populations was evaluated. The samples were collected from fields with intensive rice cultivation in Balikesir and Çanakkale provinces. Seeds were picked from barnyardgrass plants suspected to be herbicide-resistant because of their survival in the rice fields after herbicides application. A total of 38 populations were resistant to penoxsulam, and the resistance index of these populations ranged from 2 to 39. A total of 24 out of the 38 barnyardgrass populations showed a GR50 (herbicide dose causing a 50% reduction in plant dry matter) value higher than the recommended penoxsulam dose (20.2 g a.i./ha) in rice. Among these 24 barnyardgrass populations, 25, 29.2 and 45.8% populations exhibited high, moderate and low level of penoxsulam resistance, respectively. From the penoxsulam-resistant populations (38), the response of 14 populations (low to high resistance to penoxsulam) to six commonly-used herbicides for barnyardgrass control in rice was evaluated. The selected 14 populations showed resistance to almost all herbicides tested, with the lowest average resistance being determined against profoxydim and the highest average resistance against molinate herbicide. Resistance levels against six commonly-used herbicides in rice ranged from 2 to 34.