Water-seeding is a common cropping strategy in mechanized rice systems. Water-seeding of rice can suppress grass weeds, but it can encourage aquatic weeds and grass ecotypes that escape deep floodwater. In addition, water seeding prevents many cultural methods of weed control and limits available herbicides. Selection pressure from a limited palette of herbicides has resulted in widespread resistance in California rice. This study examined a novel combination of drill seeding and a stale seedbed (“stale-drill”) as a means to use a nonselective herbicide to manage weeds before rice emergence. In 2016 and 2017, rice cultivar ‘M-206’ was drilled at a rate of 120 kg ha−1 to 1.3-cm, 2.5-cm, and 5.1-cm depths. Planting rice deeper than 1.3 cm delayed emergence by 3 to 4 days. A postplant-burndown (PPB) treatment of glyphosate at 870 g ha−1 was applied just prior to rice emergence. Treatment delays had mixed effects on weed control. Glyphosate PPB was more effective at controlling Echinochloa spp. in 2017, reducing density by 30%, 48%, and 73% at 1.3-cm, 2.5-cm, and 5.1-cm seeding depths, respectively. The greatest overall weed control either year was found with glyphosate + pendimethalin followed by penoxsulam + cyhalofop at 1.3-cm planting depth. Rice stand and yield components were more strongly affected by planting depth in 2017 than in 2016, possibly owing to cool weather immediately after seeding. Yields in 2017 were reduced in deeper plantings by up to 72%. Therefore, if the stale-drill method is implemented with higher-vigor cultivars or higher seeding rates, we see potential in this method as a useful tool for reducing herbicide-resistant weeds in rice fields.
The article presents an annual field survey by the University of California as a manner of herbicide resistance management for California rice growers. Submitted weed seed samples are tested against registered herbicides which achieved no control that field season. All labelled herbicide
modes of action for each specific weed species were tested and applied according to their respective labels. Analyses of these experiments and survey data from 2015 to 2021 provide an active weed management decision-making framework for growers and a comprehensive overview of herbicide weed
management in California rice.
The continuous use of a water‐seeded cropping system for California rice (Oryza sativa L.), along with a limited palette of available herbicides, have selected for flood‐tolerant grasses, aquatic species, and herbicide‐resistant weed populations throughout the region. Alternative cropping methods such as stale‐seedbed and deeper drill seeding may be combined to allow novel herbicide modes of action and combat resistance while providing economically competitive yields. Two experiments were conducted to evaluate rice cultivars for vigorous traits that would facilitate such a stale‐drill cropping methodology. Four cultivars of California rice were grown in glasshouses and evaluated for differences in germination, elongation, emergence, and early season morphology. Cultivars M‐205 and M‐209 were found to have greater rates of total below‐soil elongation, and greater rates of mesocotyl and coleoptile elongation overall, across depths. M‐205 and M‐209 were also found to have higher rates of emergence across depths. Differences in aboveground growth parameters of emerged seedlings were only found at 0‐, 6.4‐, and 7.6‐cm planting depths. Based on observed below‐ and above‐soil growth and development, M‐205 and M‐209 exhibited greater vigor overall, as well as high levels of emergence from depths greater than 2 cm. Therefore, these cultivars should be suitable for stale‐drill seeding as a strategy for managing herbicide resistance in California.
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