Managing Herbicide Resistance Using Alternative Rice Stand Establishement Techniques

FISCHER AJ1, MOECHNIG MJ1*, HILL JE1, MUTTERS RG2, LINQUIST B1 & GREER C3;;1PLANT SCIENCES DEPARTMENT, UNIVERSITY OF CALIFORNIA, DAVIS, CA 95616, USA; 2UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION, OROVILLE, CA 95965, USA; 3UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION, YUBA CITY, CA 95991, USA; * CURRENT ADDRESS: PLANT SCIENCE DEPARTMENT, SOUTH DAKOTA STATE UNIVERSITY, BROOKINGS, SD 57007, USA.

Widespread herbicide resistance in the major weeds of rice is a serious threat to the sustainability of rice production in California. Integrating cultural and chemical weed control practices may decrease weed management costs, delay the evolution of herbicide resistance, and reduce weed seed banks. Alternative rice establishment systems have been evaluated since 2004: conventional water-seeding,conventional drill-seeding, water-seeding after spring tillage and a stale seedbed, water-seeding after a stale seedbed without spring tillage, and drill-seeding after a stale seedbed without spring tillage. These systems allowed avoidance of problematic weeds or their control by herbicides to which they are not resistant and are not used in water-seeded rice (pendimethalin and glyphosate). Aquatic sedge and broadleaf weeds dominated the water-seeded systems, while aerobic drill-seeded seedbeds favored grasses (Echinochloa spp. and sprangletop). The stale seedbed technique (promotion of weed emergence with irrigation flushes, followed by pre-plant burn-down application of glyphosate) depleted weed populations from the upper soil layer diminishing the amounts of weeds emerging with the crop. When this technique was followed by no or limited soil disturbance prior to seeding rice, average weed recruitment was reduced by 81% and 61% in water seeded and drill-seeded rice, respectively. Thus, the lowest weed infestation occurred where rice was water-seeded after a stale seedbed without spring tillage. Drill-seeding allowed for the use of pendimethalin. Rice yields did not differ among these establishment systems. Therefore, the alternative rice establishment systems evaluated in this study may be used to effectively manipulate weed species recruitment and enable the use of herbicides that may control weed biotypes resistant to herbicides used in conventional water-seeded systems. Success in weed suppression is maximized if sufficient weed emergence is promoted prior to burn-down in the stale seedbed technique and with no spring tillage. Modelling of weed recruitment and growth is being evaluated to identify rotation options that may reduce the seed-banks of problematic weed species. Results from this research will be used to develop innovative integrated weed management programs for California rice for improved sustainability and effectiveness of resistance management. Key Words: Weed management, establishment systems, herbicide resistance, weed recruitment.

See handout provided during the rice cultural sytems water quality field demonstration on August 6, 2007 in Biggs, California.