Performance of different herbicides on pondweed (Potamogeton nodosus) in rice

Abstract

Pondweed is a rhizomatous perennial weed of aquatic habitats that has recently been adopted to rice ecosystems in northern Iran. Two field experiments were conducted at the Rice Research Institute of Iran to determine the impact of pondweed on rice yield and identify effective herbicides for pondweed control. The focus of the first study was to evaluate the efficacy of herbicides commonly used in Iranian rice, including butachlor, pretilachlor, oxadiargyl, pendimethalin, thiobencarb, and bensulfuron methyl. None of these herbicides effectively controlled pondweed except bensulfuron, which reduced pondweed biomass by ≥95% and produced 26% higher rough rice grain yield than the weedy check. The second experiment evaluated the efficacy of eight acetolactate synthase-inhibiting herbicides on pondweed control, rough rice yield, and pondweed regrowth. Herbicide efficacy varied from 36% to 100%. Five preemergence soil-applied herbicides, bensulfuron-methyl, metazosulfuron, flucetosulfuron, triafamone + ethoxysulfuron, and metsulfuron-methyl provided excellent control (≥98%) of pondweed. Postemergence herbicides penoxsulam, bispyribac-sodium, and pyribenzoxim provided 36%, 89%, and 93% pondweed control, respectively. Rough rice yields ranged from 107% to 124% in herbicide-treated plots compared with the weedy check. No significant differences were detected between the rough rice yield of hand-weeded control and foliar-applied herbicide treatments, whereas yields in soil-applied herbicide treatments were higher (≥119%) than the hand-weeded control. Pondweed regrowth was affected by herbicides and was variable. Soil-applied residual herbicides metazosulfuron, flucetosulfuron, and metsulfuron provided complete control of pondweed and prevented regrowth. In contrast, pondweed regrowth in other soil and foliar-applied herbicide treatments occurred, indicating that they have less translocation to underground vegetative rhizomes. This study shows that while most sulfonylurea herbicides can control pondweed effectively to achieve high rough rice yield, only a few soil-applied herbicides were able to prevent pondweed regrowth.

Herbicides for monochoria (Monochoria vaginalis) control in transplanted rice

“…Bispyribac-sodium, penoxsulam, penoxsulam plus cyhalofop, bentazon plus MCPA, 2,4-D plus MCPA, glyphosate, and 2,4-D when applied after rice harvest were found to control monochoria by 37%, 72%, 90%, 90%, 93%, 94%, and 98%, respectively, and all of them, except bispyribac-sodium, prevented monochoria flowering and seed production (BY, unpublished data). Bispyribac-sodium is more effective at controlling small weed seedlings than weeds that have already developed (Williams 1999;Yaghoubi 2017). Excellent control of monochoria by various foliar-applied herbicides, in addition to residual herbicides, indicates that the chemical management of monochoria in rice fields is very promising.…”

“…Currently, the transplanted rice weed management program in northern Iran consists of a combination of cultural (transplanting and flooding), mechanical (puddling and harrowing), and chemical (herbicide) interventions, coupled with hand-weeding (Yaghoubi 2017), with herbicides offering the most substantial contribution. The time needed for hand-weeding a rice field is about 450 h per hectare, which can be reduced to less than 40 h by applying herbicides, indicating a more than 90% reduction in time than required for hand-weeding.…”

“…The average precipitation in this region reaches 1,200 mm, and about 80% of that occurs after the cropping season in autumn and winter. Flooding occurs in the first half of the year during the cropping season, and then continuous rain in the second half makes the rice fields suitable for subaquatic and aquatic weeds to invade the transplanted rice paddies (Yaghoubi et al 2022). Currently, some aquatic or semiaquatic weeds such as bulrush [ Bolboschoenus planiculmis (F.Schmidt) T.V.Egorova], pondweed ( Potamogeton nodosus Poir.…”

Performance of different herbicides on pondweed (Potamogeton nodosus) in rice

“…Rice production is the most dominant economic, social, and agricultural activity in the northern part of Iran (Yaghoubi and Babaei 2013) and is the main occupation and source of income for approximately 700,000 families in the region. Approximately 437,000 ha of rice fields in Iran produce 1.99 million tons of rough rice yield (FAO 2019).…”

“…It is very common in swamps, ponds, streams, canals, ditches, and freshwater marshes in many areas of northern Iran. It has recently become adapted to flooded environments of rice production systems in this area (Yaghoubi and Babaei 2013). Approximately 10 species of Potamogeton have been documented in the country (Mozafarian 2018).…”