Objectives

• Develop new chemical methods of weed control.
• Devise rice management systems that retard the competitive influence of weeds in rice.
• Learn more about weed germination, growth and development so that strategies can be improved for their control.

Rice weed control continues to be a high priority research area by the Rice Research Board. The need is not only to discover more effective herbicides but to find those that do not leave residues in drainage waters. Research emphasis in recent years has been to combine chemical and cultural practices to lessen the dependence on chemical-only control systems.

Londax, a new rice herbicide, provided 100 percent control of smallflower umbrellaplant.

There are five promising new herbicides for weed control in rice: Londax, Whip, BAS 514, Cinch and Sofit. A total of 28 experiments were conducted at four different locations, including the Rice Experiment Station at Biggs and the Rice Research Facility at Davis. Rice growers and agricultural chemical firms cooperated in these studies.

Excellent control of barnyardgrass, roughseed bulrush, arrowhead, red stem, smallflower umbrellaplant and ducksalad was obtained in three different locations using a combination of Ordram and Londax. Results were best at the 2-leaf stage of rice, but satisfactory control is possible at a later growth stage if the rate of application is increased. Londax used alone gave only partial control of barnyardgrass and excellent control of broadleaf species at rates of .5 to 1.5 ounce per acre applied at the 1- to 2-leaf stage of rice. Londax is compatible with Ordram and Bolero with respect to time of application and water management. Londax at 1 ounce per acre combined with either Bolero or Ordram at 4 pounds per acre provided nearly 100 percent weed control with a single application. Rice stands were not affected by Londax. Its low rate of application and adherence to soil particles may considerably reduce residue problems in drainage water.

Whip provided good barnyardgrass control but causes more injury to rice than Londax. Barnyardgrass control improved when Whip was applied in 10 gallons of water per acre in contrast with 40 gallons, and injury to rice was unchanged. Use of a surfactant or oil added to Whip improved weed control but caused more injury to rice. Further studies are needed with Whip to find a combination of water management and application timing to make it a useful rice herbicide. Whip is not persistent in either water or soil and should not provide a residue problem.

BAS 514 provided satisfactory weed control at 1 pound per acre or more without injury to rice when applied at the 2to 3-leaf stage of rice. Combining BAS 514 with other good broadleaf herbicides provided good broad-spectrum weed control. Further work is needed because weed control results with this chemical have not been consistent.

Studies on the germination, growth and development of weeds in rice are providing basic information that can be used for future strategies for chemical, biological and cultural practices which can be used singly or in combinations. Weed control is advancing rapidly and should eventually reduce herbicide residues in drainage waters.