Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

First Advisor

Raymond W. Schneider

Second Advisor

James L. Griffin


Field studies were conducted over three years to evaluate preplant postemergence herbicides for red rice control in rice under no-till water-seeded culture. Application of paraquat or sulfosate plus thiobencarb and paraquat alone 3 days before seeding (DBS) resulted in the greatest red rice control 11 weeks after seeding (WAS). Rice yield was increased and percent red rice in rice grain decreased when paraquat or sulfosate was applied in combination with thiobencarb compared with the nontreated control. Rice yield was increased when herbicides were applied 3 and 7 DBS as compared with 14 and 28 DBS. Aqueous extracts of cursed buttercup, low spearwort, and red rice reduced rice shoot length and dry weight at least 17 and 92%, respectively. In in vitro studies, rice radicle length and dry weight were reduced by several of the weed extracts. In greenhouse studies, addition of 16, 32, 64, 128, and 256 ppm of cressleaf groundsel extract reduced the pathogenic effect of Pythium arrhenomanes on rice by increasing rice emergence between 1.7 to 3.1 times when compared with the nontreated control. Colony radial growth of P. arrhenomanes strains was reduced between 12 and 100% with rates of 520 and 260 ppm or more of cressleaf groundsel extracts when compared with the nontreated control. Colony radial growth of P. irregulare was reduced between 23 and 43% with concentrations of 1020 ppm or more, while P. ultimum radial growth was reduced between 19 and 72% with 260 ppm or more. Weed biomass present at time of water-seeding in a no-till system can interfere with rice seed-soil contact resulting in stand reductions. The degree of rice stand reduction appears to be weed specific and is dependent on such factors as weed growth habit, herbicide susceptibility, size at application, and speed of herbicide kill. In a no-till system, soil residual injury to rice from preplant application of oxyfluorfen, 2,4-D, and triclopyr was greater under a water-seeded compared with a dry-seeded system. Quinclorac and thifensulfuron + tribenuron were least injurious to rice under both systems.