Weed Control-89



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Project Leader and Principal UC Investigators

David Bayer, professor, Department of Botany, University of California, Davis

Jim Hill, Extension agronomist, Department of Agronomy and Range Science, University of California, Davis


Researchers continued their work to fine-tune chemical management of one of the rice growers' primary cultural problems-broadleaf and perennial weed control. Specific objectives emphasized improved efficacy and safety of herbicides now in use, development of integrated rice management systems and continued study of the biology and physiology of rice weeds.

Londax® flexibility

"Londax® may have even more flexibility in waterseeded rice than originally thought."

Further study of Londax® was encouraging. From experiments conducted at the Rice Experiment Station and UC Davis, researchers concluded that Londax® may have even more flexibility in water-seeded rice than originally thought. They and others have discovered that later applications and lower rates of the herbicide successfully controlled roughseed bulrush, smallflower umbrellaplant, redstem and California arrowhead without injuring the rice. Only ducksalad required very early timing for control. Researchers emphasize, however, that earlier control is best to reduce weed competition and obtain higher yields.

Londax® also proved effective at a low rate in tandem with another herbicide from the same chemical family, Ally®. Together they controlled roughseed bulrush and partially controlled watergrass at rates of one-third to one-tenth the use rate of Londax® alone. Such combinations may eventually further reduce the amount of herbicides required to control rice weeds.

Researchers continue to be encouraged by Londax® and turn attention toward improved management strategies

Facet,® MCPA research

Water management proved to be a more significant factor in effective use of Facet®. Lower water levels improved its ability to control watergrass. More study is needed to determine how to best fit Facet® into California rice production.

Early applications of MCPA following a Londax® treatment appeared to cause significantly more injury than MCPA alone, indicating that a minimum waiting period may be needed for these two herbicides to be used together effectively.

Only two new herbicides were available for testing during 1989-one from the FMC Corporation and the other from BASF. Neither herbicide looked very promising.

Weed biology

In greenhouses, growth chambers and laboratories, scientists also turned an analytical eye to the basic biology of two important weeds-roughseed bulrush and redstem.

Apparently, one reason why roughseed bulrush is so persistent is that its rhizomes, from which the plant regenerates itself, can survive long periods of time under adverse conditions.

Researchers also determined that redstem can establish itself after germinating late in a rice stand because it grows rapidly toward the canopy, branching out and flowering among the rice panicles.

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