Comparison of the efficacy of penoxsulam with some common paddy rice herbicides

A two year study was carried out at Rice Research Institute of Iran in 2010 and 2012 in order to study the response of rice and paddy weeds to a new dual purpose herbicide penoxsulam in comparison with current used herbicides. First year treatments included penoxsulam doses in 24, 30, 36, 42 & 48 (gr.ai.ha-1), butachlor+bensulforunmethyl (BSM), butachlor+cinosulfuron and anilofos+Cinosulfuron and the second year treatments were penoxsulam at two levels (3 & 40 gr.ai.ha-1), oxadiargyl+BSM, thiobencarb (TB) and TB+BSM. All common herbicides were studied in recommended doses. Results showed penoxsulam phytotoxicity on rice 2 & 4 WAT was similar and more than current used herbicides respectively. Penoxsulam efficacy on barnyardgrass control in first and second year of trial was similar and less than current used herbicides. Also penoxsulam efficacy on sedges and broadleaf control was less than current used herbicides in both years. Decreased efficacy of penoxsulam in barnyardgrass control in the second year of study was probably because of water shortages and lack of permanent flooding. In first year of study average efficacy of butachlor+BSM or cinosulfuron to control “sedges and broadleaf” was 99, 89, and 85 % in 2, 4 and 10 WAT and penoxsulam in max recommended dose and similar rating times 61, 40 and 57 respectively. In second year of experiment penoxsulam max efficacy on ricefield bulrush (Schoenoplectus maritimus) and pondweed (Potamogeton nodusus) control was 31% and BSM in mixture with graminicides decreased their biomass more than 90% in 4-WAT. The highest grain yield 3650 kg/ha recorded in butachlor+cinosulfuron in first year. Butachlor + BSM yielded 291 kg/ha, statistically similar to hand weeded and recommended dose of penoxsulam. Dual purpose herbicide anilofos+ethoxysulfuron lacked enough efficacy on all weeds control and yielded similar to infested treatment statistically. Also the second year results confirmed the first year’s one, and showed mixture of graminicides (thiobencarb or oxadiargyl) with BSM had the highest grain yield (
3666 kg.ha-1) and penoxsulam in two investigated doses showed 25 and 48% less yield in comparison respectively. Based on results of this study penoxsulam in comparison with current used herbicides had more durable toxicity on rice, less consistency on barnyardgrass control and also lacked enough efficacy on two important perennial weed pondweed and ricefield bulrush.