Weed Control-75
 

 

 

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Project Leader and Principal UC Investigators

D.E. Bayer, Weed Control in Rice

Bill B. Fisher

D.M. Brandon

C.M. Wick

J.F. Williams

Ken Mueller

Ernie Roncoroni

N.B. Akesson, Increased Effeciency and Reducing Conamination from Chemical Applications to Rice

W.E. Yates

D.E. Bayer

Rice Co. Farm Advisors

 

CROP PROTECTION

Pest-control research projects funded by the Board have helped provide the management answers needed by growers:

  • to avoid hazards to nontarget plants (for example, to surrounding fields and orchards or to later crops grown in rotation with rice);
  • to protect downstream water quality both for agriculture and for domestic use;
  • to prevent long-term build-up of residues in treated rice fields;
  • to meet increasingly stringent state and federal air and water standards (and perhaps even influence them by providing research facts);
  • to assist profitable utilization of residue-free rice and rice by-products;
  • to assure a toxicologically "clean" operation to an environmentally alarmed public and foreign markets;
  • to make the most efficient use of costly pesticides.

The higher the potential yields of rice varieties, the greater the losses can be to diseases and insect and weed pests. Pest research generated by your Rice Research Board is outlined next.

 

þ University of California researchers and local rice farm advisors cooperated with the manufacturer of Hydrothol 191 in research that led to its registration for large-scale experimental testing in California in 1975. This new herbicide has given outstanding control of American pondweed, significantly increasing economic yield where infestations were heavy. Because regrowth of American pondweed is almost entirely from winter buds, timely applications prevent winter bud formation and suppress regrowth so that retreatment may not be necessary in succeeding years.

Competition between weeds and rice plants is most severe during early development of the rice. For example, barnyardgrass control is most critical during the first 28 to 30 days of growth of the rice plant, declining in benefits thereafter. Compounds below, soon to be registered, will assist economic weed control, improve rice yields, and increase per-acre income.

þ Tests of four new herbicides by UC weed control scientists herald a new era of chemical tools for rice weed control. Each herbicide is at a different stage of EPA clearance for use in rice. Benthiocarb (Bolero) is a useful alternate to molinate (Ordram) and controls sprangletop, ducksalad, waterhyssop, and southern naiad in addition to watergrass. Benthiocarb will be licensed for experimental field use in 1976 on about 1000 acres in California. Work in 1975 showed that bentazon (Basagran) has been very effective for the control of river bulrush, seedling cattails, and other sedges and broadleaved weeds. Bentazon also looked promising in granular combinations with molinate. Bentazon is already registered for commercial use on soybeans in southern states, and it is likely to be approved for commercial use on rice in California and the southern states under EPA experimental permit in 1976. Glyphosate (Roundup) is very effective in controlling mature cattails, dallisgrass, johnsongrass, and other weeds on rice levees. Drepamon applied preflood and early postflood looks very promising for the control of barnyardgrass and sprangletop besides showing some activity against redstem and roughseed bulrush. These last two compounds will likely not receive California rice-use registration in 1976.

As soon as Bolero, Roundup, Basagran, and Drepamon become available for use in California rice production, research will already have developed details on how and when to use each herbicide.

Three trials were conducted in Yuba County to evaluate MCPA injury on rice in relation to time of nitrogen fertilizer application and the resulting influence on rice root development. Two major trends were apparent: 1) Late applications of MCPA (65 days after seeding) were more injurious to yields than were earlier applications (35 to 45 days after seeding). 2) Top-dressing with nitrogen 10 days before, at the time of, or 10 days after applying MCPA had no apparent effect on rice yields. Laboratory studies have shown a high correlation between rice root development and injury related to MCPA. Rice that is healthy at the time of application and has a well developed root system shows little or no injury, whereas rice with a reduced root system shows more severe symptoms. The increased yield from the early application of MCPA results from the reduction of weed competition.

Cooperative studies with the Department of Agricultural Engineering on ways of controlling or reducing drift have suggested that thickeners such as Nalco-Trol reduce drift but do not eliminate it. A helicopter equipped with a Microfoil boom applied propanil to a 100-acre field for barnyardgrass control in rice. Propanil drift was reduced but not eliminated; yellow spotting developed on young prune trees nearby. Ground-rig-applied propanil data (incomplete) show no damage resulting to adjacent prune trees and that spotting would be unlikely beyond 1/2 mile. More tests with ground-rig-applied propanil are needed in 1976.

þ Granular formulations of Ordram, Bolero, and Drepamon performed better than sprayable formulations applied at the same times and rates, although the weed control and yield increase differences were not as great as found last year with Ordram and Bolero.

Other (currently unregistered) herbicides continuing to show promise were Simetryn, and perfluidone (Destun); and preliminary trials indicated that 3 additional compounds may also be useful. Simetryn was found very promising as an algacide, as a submersed or emerged aquatic herbicide, as an additive to other herbicides in seed coatings, and in granular combinations with molinate, benthiocarb, or Drepamon. Perfluidone gave good broad-spectrum weed control but further work is needed to learn how it should be used more safely and effectively under California conditions.

Among phenoxy-acid herbicides that are currently registered and might be considered for use in rice as alternatives to MCPA in areas approved for such phenoxy applications, formulations of silvex and 2,4,5-T were found more safe and efficacious than formulations of 2.4,-D. Silvex was of special interest because it gave nearly as good control of river bulrush as bentazon, so it could be used for that purpose until bentazon becomes available.

 

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