Efficacy of some new herbicides for barnyardgrass controlling (Echinochloa crus-galli (L.) P. Beauv) in different rice genotypes

Abstract

Background and Objectives: Barnyardgrass is the most important and most abundant weed of paddy fields in Iran and chemical control (butachlor) play a major role in its management. The usage of butachlor in most rice growing countries is restricted or prohibited due to health and environmental hazards, and its production and trade in Iran will be banned in the next future. Due to the dangers posed by widespread usage of herbicides integrated weed management with more weed competitive varieties to reduce herbicide dependence is taken into consideration. This study aimed to study the efficacy of some new herbicides for introducing as a substitute for butachlor and also to investigate the effect of rice cultivar on herbicide performance. Materials and Methods: The experiment was conducted as a factorial experiment based on randomized complete block design with three replications at Rice Research Institute of Iran-Rasht in 2018. Factors included rice genotypes (Hashemi, Khazar and Line 203 “Line”) and herbicide type (recommended dosage of butachlor, clomazone, pendimethalin and flucetosulfuron herbicides). Moreover, hand weeded and weedy plot were included to the experiment as controls. Results: The barnyardgrass biomass and rice yield were affected by rice genotype, herbicide type and their interaction. The barnyardgrass biomass in weedy control in Khazar, Hashemi and Line cultivars was 227.7, 246 and 334 g m-2, respectively, which in Khazar and Hashemi cultivars was 57% and 16% higher, compared with line respectively, indicating different ability of cultivars to inhibit the barnyardgrass growth. The reduction in grain yield of rice in weedy control in Khazar, Hashemi and Line cultivars was 63, 74 and 87%, respectively, compared to hand weeded control. More reduction in line grain yield despite more inhibitory effect on barnyardgrass is due to late maturing of this line and longer period of interference with barnyardgrass. The dry weight of barnyardgrass in plots treated with pendimethalin was similar to or less than the treatments treated with butachlor, flucetosulfuron and clomazone. Also rice yield in all genotypes in plots treated with pendimethalin herbicide was not statistically different from that in the plots treated with butachlor and hand weeded control treatment. The good efficacy of pendimethalin in controlling barnyardgrass and producing grain yield similar to butachlor and hand weeded control indicates the potential of this herbicide to be introduced as a replacement for butachlor. Also, the yield of line in plots treated with clomazone and flucetosulfuron was statistically similar to the yield of hand weeded control plot, while the yield of Hashemi and Khazar cultivars in plots treated with the two new above mentioned herbicides were significantly lower than hand weeded control. These results indicate the competitive advantage of line over Hashemi and Khazar cultivars in barnyardgrass control. Conclusion: In the last decade, more than 95 percent of paddy fields in the north of the country have been treated with butachlor herbicides for chemical control of barnyardgrass. In recent years, concerns have been raised about the adverse effects of butachlor on the health of the community and the environment, and the herbicide will be removed from the countries authorized pesticides list in the near future. Due to the good performance of pendimethalin in barnyardgrass control and the high grain yield in treated plots with this herbicide, it could be introduced as a butachlor substitute for barnyardgrass control in Iranian rice fields, although the cultivation of new competitor cultivars will also contribute to be successful.