ALTERNATIVE RICE STAND ESTABLISHMENT TECHNIQUES FOR MANAGING HERBICIDE RESISTANCE AND WEED RECRUITMENT

Five rice stand establishment systems have been evaluated yearly in northern California since 2004: 1) conventional water-seeded rice, 2) conventional drill-seeding, 3) water-seeding after spring tillage and a stale seedbed, 4) water-seeding after a stale seedbed without spring tillage, and 5) drill-seeding after a stale seedbed without spring tillage. Aquatic sedge and broadleaf weeds dominated the water-seeded systems, while the aerobic drill-seeded systems favored Echinochloa species and Leptochloa fascicularis. The stale seedbed technique (promotion of weed emergence with irrigation flushes, followed by pre-planting application of glyphosate) depleted weed populations from the upper soil layer and diminished weed emergence with the crop. If this technique was followed by no or limited soil disturbance prior to seeding rice, weed control required thereafter was minimal. In a fifth year, when drill-seeded plots with heavy E. crus-galli and L. fascicularis infestations were switched to water seeding after a stale seedbed without spring tillage, weeds were almost eliminated using only glyphosate.