Browsing by Author "Fischer, Albert"

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    Resistance to Bensulfuron-Methyl in Water Plantain (Alisma plantago-aquatica) Populations from Chilean Paddy Fields
    (CAMBRIDGE UNIV PRESS, 2008) Figueroa, Rodrioro; Gebauer, Marlene; Fischer, Albert; Kogan, Marcelo
    Bensulfuron-methyl (BSM) has been one of the most widely used herbicides in Chilean rice fields because it controls a wide spectrum of weeds and does not require field drainage for application. However, failures of BSM to control water plantain in rice fields have been noted since 2002. We assessed BSM effects on suspected resistant (CU1 and CU2) and Susceptible (AN I) water plantain accessions collected in Chilean rice fields during 2004 and 2005. BSM rates resulting in 50% growth reduction (GR(50)) of CU2 and CU1 plants were 12- and 33-fold higher than for ANI plants, respectively. Acetolactate synthase (ALS) activity assays in vitro Suggested resistance in CU1 and CU2 was due to an ALS enzyme with reduced BSM sensitivity compared to the AN I biotype. Resistance indices (RI), or ratios of the resistant to susceptible I-50 values (BSM rate to inhibit ALS-enzyme activity by, 50%), were 266 (CU2/AN1) and > 38,462 (CU1/AN1). This agreed with in vivo ALS activity assays where RI were 224 (CU2/AN1) and > 8,533 (CU1/AN1). Resistance levels detected in whole-plant or in vivo ALS activity assays were orders of magnitude lower than those detected in in vitro ALS activity studies suggesting nontarget site mechanisms may have mitigated BSM toxicity. However, a consistent ranking of BSM sensitivity levels (AN1 > CU2 > CU1) throughout all three types of assays suggests resistance is primarily endowed by low target site sensitivity. We conclude that Susceptible and resistant water plantain biotypes coexist in Chilean paddies, and the use of integrated weed management involving herbicides with a different mode of action would be imperative to prevent further evolution of resistance to BSM and possibly cross-resistance to other ALS inhibitors. In vitro ALS-enzyme assays provided the best discrimination of resistance levels between biotypes.
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    Using penoxsulam ALS inhibitor as a broad - spectrum herbicide in Chilean rice.
    (2011) Kogan Alterman, Marcelo; Gómez, Patricio; Fischer, Albert; Alister Herdener, Claudio Andrés
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    Using penoxsulam ALS inhibitor as a broad-spectrum herbicide in Chilean rice
    (2011) Kogan, Marcelo; Gomez, Patricio; Fischer, Albert; Alister, Claudio
    M. Kogan, P. Gomez, A. Fischer, and C. Alister. 2011. Using penoxsulam ALS inhibitor as a broad-spectrum herbicide in Chilean rice. Cien. Inv. Agr. 38(1): 83-93. The continuously-flooded rice production system in Chile has selected highly competitive aquatic weeds selection capable of reducing paddy yields by 25 to 50%. Penoxsulam is abroad-spectrum triazolopyrimidine (ALS inhibitor) commercially introduced in Chile in 2006, where Alisma plantago aquatica hads already evolved resistance to sulfonylurea herbicides (SU). Several field trials with water seeded rice were conducted during 2003 and 2004 in Chile to determine efficacy, timing of application, spectrum of control, and control of SU-resistant A. plantago aquatic(a with the herbicide penoxsulam, either in single applications or in sequence with other herbicides. Penoxsulam was applied a) 12 days after seeding (DAS) into the water (I W), b) in postemergence after draining the water from field (ADW) at 35 DAS ore) IW followed by ADW applications of MCPA, cyhalofop, bentazon, or triclopyr. Penoxsulam was tested at 20, 30, and 40 g a.i. ha(-1). Comparisons were made with recommended rates of other IW treatments (metsulfuron, bensulfuron and cyclosulfomuron) and sequential applications of molinate (IW) followed by ADW applications of MCPA, cyhalofop, bentazon, or triclopyr. One IW penoxsulam application was sufficient to achieve broad-spectrum control: Echinochloa spp. (100% control), A.plantago-aquatica (80 to 100%), Schoenoplectus mucronatus (50 to 80%), and Cyperus difformis (80 to 100%). Rice yields in penoxsulam-treated plots were 30 to 56% higher than in the untreated controls. Yields with penoxsulam IW (all rates) were similar (P > 0.05) to those obtained using molinate (IW) followed by ADW applications of bentazon or MCPA. Although penoxsulam is an ALS inhibitor, it controlled A. plantago-aquatica resistant to metsulfuron and bensulfuron.