Baseline sensitivity of penoxsulam to Echinochloa spp. accessions from Italian rice fields

Penoxsulam (triazolopyrimidine) is a new selective ALS-inhibitor herbicide for weed control in dry-seeded, water-seeded and transplanted rice, with high efficacy against Echinochloa species. The sensitivity to penoxsulam of nine Echinochloa populations collected in Italian rice fields was assessed in a dose-response study carried out in the greenhouse. The herbicide was applied at eight rates ranging from 0 to 160 g a.i. ha﷓1. Fresh weight and visual efficacy were assessed 21 days after treatment. The data of each population were expressed as percent of untreated control plants and fitted to a log-logistic model. The rates of herbicide for 80% and 90% of plant growth inhibition (GR80 and GR90, respectively) where calculated from the fitted equations.All tested populations showed to be highly sensitive to penoxsulam, with the highest level of control generally reached already at 20 g a.i. ha﷓1. The GR80 ranged between 2.7 and 9.8 g a.i. ha﷓1, while GR90 ranged between 3.2 and 19.2 g a.i. ha﷓1.