Weed Control - 92 




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Project Leader and Principal UC Investigators

David E. Bayer, professor, Department of Botany, OF Davis

James E. Hill, extension agronomist, UCD Agronomy & Range Science

Theodore C. Foin, professor and chair, UCD Division of Environmental Studies

Principal UC Investigators

J. Webster, research associate, UCD Agronomy & Range Science

E. Roncoroni, research associate, UCD Department of Botany

S. Scardaci, UC Cooperative Extension farm advisor, Colusa/ Glenn/Yolo counties

C. Wick, UC Cooperative Extension farm advisor; Butte County

J. Williams, UC Cooperative Extension farm advisor, Sutter/ Yuba Counties

J. Breen, research assistant, UCD Agronomy & Range Science

G. Fitzgerald, research assistant, UCD -Agronomy & Range Science

T. Kraus, research assistant, UCD Agronomy & Range Science 

The biology of weeds important to rice culture, development of an integrated management system for weed control, and the effectiveness of new and existing herbicides are the three guiding objectives of this critically important ongoing research project. News that some weeds - California arrowhead and smallflower umbrellaplant - may be developing resistance to Londax®, is giving herbicide research a renewed sense of urgency.

Experimental herbicides

Findings from last year's examination of experimental herbicides include:

  • AC 322,140 effectively controlled broadleaf and sedge weeds, but slightly injured rice.
  • KIH 2023 provided acceptable watergrass control only up to the four- to five-leaf stage.

However, both these herbicides inhibit the same biochemical process in weeds as Londax®, thus limiting their potential for further study because of the resistance problems noted above..

Facet®'s facets

Continuing studies of Facet® produced contradictory results. In previous experiments, Facet® was unable to control watergrass alone. In 1992, however, this compound, provided adequate watergrass control in applications of 4-8 ounces active ingredient per acre. . Researchers have no explanation for the difference in control. In a related experiment, combinations of Facet® with low rates of Ordram® or Bolero® controlled watergrass - as it has in previous years.

Herbicide combinations

Preplant incorporated (PPI), treatments of Ordram® in combination with Londax® proved successful for the third consecutive year. Both PPI applications of Ordram® and a preflood surface (PFS) application of Bolero® controlled watergrass in combination with Londax®. Without Londax® however, watergrass control was unacceptable.

Efficacy studies

In the interest of limiting worker exposure during handling and loading, researchers tested two 15G formulations of Ordram® for dust emission and efficacy. Both were equal in weed control but one formulation rated better for dust emission.

Another experiment on preflood surface (PFS) applications of liquid Bolero® indicates that for best results it should be incorporated by the floodwater within three days of application.

Several. herbicides were tested in combination with Londax® for late, postemergence control of watergrass. Whip®, Poast® and KIH 2023 effectively controlled watergrass as late as the four-to five-leaf stage.

Growth model

Researchers have also developed growth models to predict the effectiveness of different weed management strategies. Their results, supported by experimental data, show that some important weeds, such as smallflower umbrellaplant and watergrass, should be controlled as early as possible. Other visually important weeds, such as annual arrowhead, are unlikely to have a significant impact on the rice crop.

Weed competition

An experiment to determine how weed abundance affects stand establishment confirmed that grass weeds are highest in drill-seeded rice and aquatic weeds are highest in water-seeded rice. In drill-seeded rice, competition from grass weeds was much higher than competition from broadleaf weeds in waterseeded rice, thus necessitating the use of grass herbicides to achieve a reasonable yield. If herbicides were unavailable, rotation between waterseeded and drill-seeded rice may provide some help in combatting weeds in fields where grass populations are low.

In greenhouse experiments researches were able to determine that the best method for applying the experimental grass herbicide KIH 6127 is through a preflood surface treatment and increased water depth.

Weed biology

In laboratory studies researchers found that the greatest number of apical buds on perennial arrowhead germinate while remaining buds lie dormant. Laboratory work also determined that ricefield bulrush can regenerate from rhizomes for several seasons, which explains this weed's pesistence. Ricefield bulrush arising from rhizomes also require higher rates of Londax® for their control.

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