Weed Control 90

Weed Control-90

Project Leader and Principal UC Investigators

D.E. Bayer, Professor, UC Davis

J.E. Hill, Extension Agronomist, UC Davis

S.R. Roberts, Staff Research Assoc., UC Davis

E. Roncoroni, Staff Research Assoc., UC Davis

S.C. Scardaci, Farm Advisor, Colusa County

J. Brandon, Laboratory Assistant

N. Itchizen

J. Breen, Research Assistant

To enhance California rice growers' ability to control weeds, researchers focus on three general objectives:

Always of central interest to growers are recent developments in use of rice herbicides. Combinations of Londax® with other herbicides were studied this past season.

Develop new chemical methods of weed control and improve the efficacy and safety of herbicides in use.
Continue development of an integrated rice management system for weed control.
Study the biology and physiology of rice weeds.

Continuing studies of Londax® indicate that lower than label rates and later application timing may control broadleaf weeds and sedges when preferred or necessary. In one experiment, Londax® controlled ricefield bulrush at the two, four and six leaf stage, but not at 30 days after seeding. Also no differences in ricefield bulrush control were observed at rates of 3/4 oz/A. Thus, growers who monitor weed growth and make timely applications, have low weed infestations or can justify it economically, may be' able to use less than label rates.

Because of the inconsistencies with preplant incorporated (PPI) Ordram® in controlling watergrass, growers typically use it in a postemergence application. But this increases the potential for residue to escape in ricefield drain water. An experiment was designed to determine the effectiveness of Londax® in controlling watergrass missed by a PPI application of Ordram®. Applied PPI at 3 lb/A, Ordram® alone gave moderate control. However, Ordram® applied PPI and followed by Londax® at 1 oz/A controlled watergrass 99 percent.

Early weed removal with Londax® also appears to improve nitrogen use efficiency by eliminating competition for nitrogen by the weeds. Similar yields were obtained at approximately 30 pounds less nitrogen in Londax® treated plots compared to MCPA treated plots. Details of this experiment are contained in the section summarizing the work of the rice breeding program.

Londax® studies support lower rates, later timing and enhanced nitrogen efficiency.

Combinations of Facet (BAS 514, an experimental rice herbicide) with Ordram® or Bolero® for watergrass control look promising, especially in view of the erratic results of Facet alone in previous studies. In one study to improve herbicide use, water was lowered one to two inches before herbicide application and maintained at that level for 60 days following treatment. Facet was then applied as a spray and followed with Ordram® or Bolero®. The Facet-Ordram® combination gave about 10 percent better watergrass control than the Facet-Bolero® plus Ordram® combination.

Although combinations of Facet with either Ordram® or Bolero® were more effective than combinations of Facet with Londax®, the latter combination gave near perfect control of rice field bulrush.

Other developments in weed control include:

Studies with the late postemergence grass herbicides, Poast® and Whip®, showed relatively poor watergrass control.
Greenhouse studies indicate that rice field bulrush is especially competitive once the weed canopy is allowed to reach the same height as rice.
A population of rice field bulrush reported to be resistant to Londax® in 1989 was found to be susceptible to the herbicide in a greenhouse experiment.
A new postemergence foliar-applied experimental herbicide looked promising for watergrass control at rates well below those of currently used herbicides.