Environmental Fate of Herbicides-75
 

 

 

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Project Leader and Principal UC Investigators

D.E. Cosby, Dept. of Toxicology, UC Davis

J.B. Bowers

C.J. Soderquist

William Draper

 

The Rice Research Board funded a UCD project on the environmental fate of herbicides so as to ensure maximum safety to people and the environment while controlling rice pests with chemicals. There are three objectives:

  1. To identify the environmental factors which govern the transport and chemical transformations of rice pesticides.
  2. To examine the distribution and dissipation of a pesticide in a rice field.
  3. To estimate the importance of environmental factors, to field application and the significance of pesticide decomposition products.

Previous findings in the UCD Environmental Toxicology Laboratory facilitated the EPA decision to retain MCPA for control of broadleaved weeds in California rice fields. Each year one or more chemicals are singled out for intensive research. Receiving major attention in 1975 was molinate (Ordram).

þ Ordram's environmental fate: about 90% of a post-flood application of Ordram (molinate) goes into the water, while 10% goes into the top 2 inches of soil. The soil residue remains unchanged for several months but the Ordram in the water is half gone in 3 days and 98% gone in 13 days. A final distribution shows 10% in the soil, where it is probably destroyed by microorganisms, 1-2% in rice plants and weeds, 4-5% photoxidized by sunlight, and 80-85% going into the atmosphere as vapor. Volatilization increases sharply as water temperatures rise.

 

A new chemical, bentazon, continues to show remarkable ability to control broadleaved weeds and cattails. Area free of weeds received 1 lb active ingredient bentazon after rice emergence.

READY-REFERENCE LISTING OF CHEMICALS FOR RICE PEST CONTROL:

Table 2 lists the status of the principal chemicals which have been tested for the control of rice yield-reducing pests. Many of these chemicals are mentioned in this report. Note that some are not yet registered for use, some are registered, and some have registrations pending. Consult your local agricultural commissioner concerning the current status and for use permits for those you need to use. Be sure you and your applicator follow the manufacturer's labeled instructions.

 
Table 2. 1976 status of chemicals useful in rice pest control*
HERBICIDES
Registered
  • Copper sulfate (several mfrs.): algae
  • MCPA (several mfrs.): broadleaved weeds
  • Ordram® (molinate) (Stauffer Chem. Co.): barnyardgrass
  • Silvex (several mfrs.): broadleaved weeds; river bulrush
  • 2,4,5-T (several mfrs.): broadleaved weeds
Registered for use south of Sankey Road Propanil (several mfrs.): barnyardgrass; broadleaved weeds; sedges
Registry applied for Basagran® (bentazon) (BASF): seedling cattails; sedges; river bulrush, broadleaved weeds
Exptl. label for 1000 acres in '76 Bolero® (benthiocarb) (Chevron Chem. Co.] barnyardgrass, sprangle. top; seedling cattails
Exptl. label received 1975 Hydrothol 191® (Pennwalt Corp, American pondweed and some other aquatics
Not registered for in-crop growing-season use Roundup® (glyphosate) (Monsanto Chem. Co.): rice levee weeds, including mature cattails
Not registered
  • Destun® (perfluidone) (3M): grasses and broadleaves; early postflood
  • Drepamon® (Hercules Chem. Co.): barnyardgrass; sprangletop
  • Simetryn® (CIBA-Giegy): algae; and in combination with other herbicides
FUNGICIDES
Registered
  • Captan SP®; Orthocide 50® (captan) (several mfrs.): seed treatment for seedling diseases
  • Difolatan 4F® (folcid) (Chevron Chem. Co.): seed treatment for seedling diseases
Registry applied for Du-ter® (triphenyletin hydroxide) (Thompson-Hayward Chem. Co.): stem rot
INSECTICIDES
Registered
  • Copper sulfate (several mfrs.): tadpole shrimp; algae
  • Malathion (several mfrs.): rice leaf miner
  • Parathion n (several mfrs.): tadpole shrimp; rice leaf miner; mosquitoes
  • Sevin® (carbaryl) (Union Carbide Chem. Co.): tadpole shrimp; leafhoppers
Registered for preflood and drained-field use Bux® (no generic name) (Chevron Chem. Co.): water weevils
Registered preflood only Furadan® (carbofuran) (Food Machinery Corp.): water weevils
Registered for mosquitoes only Lorsban® (Dursban® - chlorpyrifos) (Dow Chem. Co.): mosquitoes and midge larvae
Not registered Mesurol® (Chemagro Co.): midge larvae (not effective as seed treatment)
*Potential uses include some for which the compound may not currently be registered. See introductory paragraph to this section.

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