Rice

Weed Management

Control Measures

Thorough puddling, proper levelling and irrigation management control germination and growth of weeds. Working with rotary weeder (push hoe) in line planting rice at 20,30 and 40 days of crop growth. Manual weeding (common practice) in random planting rice at 20 and 30 days after transplanting. Manual weeding is costly and also due to non-availability of labor now-a-days,other methods of weed control gaining importance.

Application Techniques

Herbicides which are in liquid and wettable powder formulations are applied with the help of knapsack sprayer by using flat-fan nozzle or impact nozzles otherwise known as deflected nozzles or floodzet nozzles. The application is usually made at low pressures ranging 15-25 PSI to avoid drift. To be more careful for avoiding drift to the plant portions, a protective shield may also be fixed over the nozzle. The herbicides with granular formulations are usually broadcasted by mixing with sand for obtaining even distribution. Sometimes when the sprayers are not readily available the liquid formulations at the rate of 1 lit is mixed with 20-25 Kgs of sand and broadcasted uniformly by maintaining 2 cm layer of water. Equipment used Hand sprayers The following procedure may be used to calibrate a sprayer having a relatively small spray tank capacity, such as the 2 to 5 gallons size commonly carried by hand, on the shoulder, or as a backpack. To properly calibrate such sprayer, they must be equipped with a pressure regulation valve located between the spray tank and the nozzle outlet so that a constant sprayer output maintained. Pour a known volume of water into the spray tank. Close spray tank and pump up pressure. At constant pressure and uniform speed, spray a known area. Determine the sprayer output for the area by substracting the amount of water remaining in the spray tank from the amount originally poured in the tank. Sprayer output for a given area may be adjusted by changing the pace or the nozzle orifice size or both. Generally the spray pressure remains set at about 25 Psi. If necessary, the sprayer output can be expressed as gal/A by dividing the area A (43,560ft2) by the area spayed (ft2), multiply this value by the volume of  water applied / area and conversion of gallons. (1gal = 128 fl oz = 3,785 ml) 1 fl oz = 29.57ml. The following procedure may be used to calibrate sprayer equipped with any type of spray nozzle designed to cover uniformly a given area with the spray mixture, at constant speed and spray pressure. Fill the spray tank completely with water. Select a safe speed (use bet 2 and 5 mph) for the terrain to be sprayed and use this speed during calibrations. Make off any convenient distance. Generally, the greater the distance the greater is the accuracy in determine sprayer output. Make one or more passes with the spray over the measured distance at the selected speed operation the sprayer only over measured distance. Determine the volume of water applied to the area by refilling the spray tank to its original water level and carefully note the no. of fluid ounces required. Calculate the area sprayed by multiplying the width of the area sprayed by the distance travelled measured in feet. Divide the no. of square feet in / A (43,560) by the no. of square feet in the area sprayed to obtain the no. of such plots / area. Multiply the no. of plots / area by the no. of fluid ounces applied / area. Divide the total no. of fluid ounces of water applied / area by the no. of fluid ounces in 1 gal (128fl oz) to obtain the sprayer output expressed in gallons of water / area. Machine (power ) sprayer calibration Proper sprayer calibration is essential to the application of the correct amount of herbicide. The volume of carrier applied by sprayer is governed by a 5 factors Speed of the sprayer and the area to be sprayed. Spray pressure used. Number of nozzles used. Size of the nozzle orifice opening. Viscosity of the liquid. Increasing the speed of the sprayer over the area sprayed (other factors remaining constant) results in less carrier applied to the area. Slower speed results in the application of a greater volume of carrier. The more commonly used speeds of ground equipment are between 2 and 5 miles/hr depends on lands. With other factors remaining constant, increasing the spray pressure results in a greater volume of carrier being applied to a given area. Conversely, a lower spray pressure results in less carrier applied. On general spray pressure of 15 to 40 ponds / square inch are used when applying weedicides. With the other factors remaining constant, any increase in the no. of nozzles used with the sprayer results in increased sprayer output. Added nozzles, however do not necessarily increase the volume / area applied. They may be spaced nearly to increase the area covered during each of the sprayer. Similarly a decrease in the no of nozzles used usually results in a smaller area sprayed, rather than a change in a vol / area. With the other factors remaining constant, the use of larger-size orifice nozzle tips results in a greater vol. of carrier being applied to a given area. Smaller size orifice tips will deliver a smaller vol. of carrier. With the other factor remaining constant, the lower the viscosity of the liquid carrier the greater the volume of carrier (or spray mixture) applied to a given area.The greater the viscosity the less applied. The most practical mean of changing sprayer output during calibration is to change the speed ornozzle orifice size or both. When adjusting sprayer output during calibration , it has been in mind that spray droplets become smaller as the spray pressure is increased or nozzle orifice size is decreased. The smaller the spray droplets, the greater is their tendency to drift from the target area with air movement. For uniform spray covers, proper nozzle tips must be used and the nozzle spacing must be adjusted properly for the land involved. Nozzle tips of the same orifice size must be used in all nozzles of the spray boom, otherwise sprayer output will not be uniform. Herbicide dosage calculations In general, the first steps in the procedure for calculation herbicide dosage are to be known. Which herbicide(s) to use for best results under your particular set of conditions. What the recommended dosage is for the herbicide How much herbicide(s) present in a given quantity of the commercial product to be used. The following general formulas may be used for solving most herbicide dosages. For liquid Formulations (Soluble, emulsifiable , flowable (slurry)) Pounds of active gradient / gallon of formula For dry formulate (wettable powder, granular pellets) Significance of symbols on the herbicides label Toxicity category Actual-oral toxicity LD50 mg/kg Color of Triangle Signal-word required on label Warnings symbol on the label Extremely toxicity 0 - 50 Red Poison Skull and cross bones Highly toxicity 51 - 500 Yellow Poison - Moderately toxicity 501 - 5000 Blue Danger - Slightly toxicity 5000 Green Caution -

Weedicides used in Rice

Benthiocarb

Chemical name: S - (4 - chlorophenyl) methyl dithyl - carbamotriate.

Common name: Benthiocarb (proposed withdrawn from ANSI) thiobencarb is being proposed.

Other name: Saturn, Saturno.

Action: pre emergence and early post emergence herbicide.

Chemical properties: Less soluble in water, very soluble in xylene, alcohol and acetone.

Toxicity: Acute oral LD50 (rat) 1903mg/kg

Signal word Caution:

Application Pre-emergence and early post-emergence herbicide for control of grasses, broad leaf weeds which infest rice fields, both wet seeded and dry seeded.

Formulations: E.C , 10% G.

Butachlor

Chemical name: 2 chloro - 2,6 - diethyl - N - (butoxy - methyl) acetanilide.

Common name: Butachlor

Other name: CP53619.

Action: Selective pre-emergence herbicide.

Chemical properties: Amber coloured oily liquid soluble in water specific gravity 16.5 at 250C

Toxicity: Acute oral LD50 (rat, 3120mg/kg; Dermal LD50 (rabbit) 2510 to 5010mg/kg

Signal word Caution: Application For pre-emergence control of annual grass and certain broad leafed weeds in both transplanted rice grown in certain Asian and South American area.

Formulations: 5% G, E.C

Oxadiazon

Chemical name: 2 - tertiary - butyl - 4 - (2,4 - dichloro - 5 isopropoxyphenyl), 2 1,3,4 - Oxadiazolin - 5 -one

Common name: Oxadiazone.

Other name: RP17623

Properties: White crystals M.P. at 88 - 900C insoluble in water soluble in Chlorinated hydrocarbons.

Toxicity: Acute oral LD50 in rats, greater than 8000mg/kg

Signal word Caution: Pre-emergence and early post-emergence control of annual grasses and broad leaf weeds.

Formulations: E.C and Granules.

Fluchloralin

Chemical name: N - (2 - chloro ethyl - a, a, a, - trifluro, - 2,6 dinitro  - N propyl - P - toluidine.

Common name: Fluchloralin

Action: Pre - plant incorporated herbicide

Chemical properties: Orange - yellow crystalline solid. M.P 42 - 730C

Toxicity: Acute oral LD50 (rat) - 1500mg/kg. Low order of toxicity to  wild fowl. Toxic to fish.

Signal word Caution: Antidote Treat symptomatically

Application Pre-plant and pre-emergence incorporated, for the control of annual grasses and certain broad leaf weeds

Formulations: E.C

2,4 - D

Chemical name: Lithium 2,4 - dichlorophenoxy acetate

Chemical properties: Non - volatile, water soluble metal salt

Toxicity: Acute oral LD50 (rat) - 850mg/kg.

Signal word Caution: Application Used as a post-emergence application for the control of  broad leaf weeds

Formulations: 5% G.

Lolop Granules

Chemical name: Pytolidynyl 2,4 - dichlorophenyl carbomate

Chemical properties: Approx. 850ppm soluble in water boils at  154 - 1550C Action Herbicide for paddy weeds

Toxicity: Acute oral LD50 (mouse) - 850mg/kg.

Formulations: 5% G

Nitrofen

Chemical name: 2,4 - dichloro phenyl P - nitrophenyl ether

Common name: Nitrofen

Other name: NIP

Action: Pre or post emergence

Chemical properties: M.P 62 - 650C

Toxicity: Acute oral LD50 (rat) - 2630mg/kg.

Application: Control of no. of weeds in rice. Incorporation not recommended.

Formulations: E.C 25%, W.P 50% and 7.7% G

MCPA

Chemical name: 4 - chloro - o - methyl oxy acetic acid

Common name: MCPA, metaxon

Other name: Agroxone, Rhonox

Action: Herbicide (hormone type)

Chemical properties: Like 2,4 - D except for replacement of one chlorine atom by a methyl group M.P 118 - 1190C soluble in water at room temp is 825ppm

Toxicity: Acute oral LD50 (rat) - 700 - 800mg/kg. Mouse 550mg/kg

Antidote: None, remove poison by inducing vomiting

Application: A translocated herbicide used as post-emergence for the control of annual and perennial broad leaf weeds

Formulations: Combinations With various free hormone type herbicide

Propanil

Chemical name: 3,4 - Dichloro phenyl propionanilide

Common name: Propanil

Other name: Bay 30130, Chemrice

Action: Selective post-emergence herbicide (contact type)

Chemical properties: Dark oily liquid M.P 90.6 - 91.60C

Toxicity: Acute oral LD50 (rat) - 1384mg/kg.

Application: For post-emergence application to kill barnyard grass and various water weeds in rice

Formulations: E.C 2%, 25%

Combinations: Propanil plus wydac

Propanide

Common name: Propanide

Action: Post-emergence herbicide

Chemical properties: It is crystallized substance slightly soluble in water, more soluble in organic solvents M.P 91 - 920C

Toxicity: Acute oral LD50 (rat) - 1300mg/kg.

Application: Effective for the control of barnyard grass

Bentazon

Chemical name: 3 - isopropyl - 1, H - 2, 1, 3 - benzothiadiazin (4) - 3H - one   2, 2 dioxide

Common name: Bentazon

Action: Herbicide

Chemical properties: White crystalline. M.P 132 - 1390C soluble in water, (0.05%), ethanol (86.1%), benzene (3.3%)

Toxicity: Acute oral LD50 (rat) - 1120mg/kg.

Signal word Warning: Application Selective post-emergence control of broad leaf weeds

Formulations: Soluble concentration as the sodium salt of bentozone

Pendimethaline

Chemical name: N - (1 - ethyl propyl) - 3,4 dimethyl - 1,2,6 dinitro benzenamine

Common name: Pendimethaline

Other name: Prowl, stomp

Action: Selective herbicide

Chemical properties: Orange - yellow crystalline M.P 54 - 580C soluble in water less than 0.5ppm at 200C soluble in chlorinated hydrocarbon and aromatic solvents

Toxicity: Acute oral LD50 (rat) - 1250mg/kg,    Dermal LD50 (rabbit) >5000mg/kg

Signal word Caution: Application Selective pre-plant incorporated - pre-emergence herbicide for the control of annual grass weeds and certain broad leaf weeds

Formations: E.C WP, G

Paraquat

Chemical name: 1,1-Dimethyl-4,4- bipyridinium ion Present as the dichloride salt.

Common name: Paraquat.

Other names: Dextrone, Gramoxone

Action: Contact herbicide & desiccant

Chemical Properties: The dichloride salt is freely soluble in water,sparingly in lower alcohols, Insoluble in hydrocarbons. Stable except under alkaline conditions. No measurable vapour pressure strongly absorbed and inactivated by soil particles.

Toxicity: Acute oral LD 50(rat), 150mg/kg

Aplications: For desiccation of seed crops, for non crop and industrial weed control in bearing and non-bearing fruit orchards, shade trees, and ornamentals. For killing potato vines and aquatic weed control. Formulations: Soluble dichloride conc (2 pounds/1000 gallon) Weedol is a granular formulation containing 2.5% w/w Paraquat ion as the dichloride salt with diquat

Dalapon

Chemical name: 2-2 dichloro propionic acid

Common name: Dalapon

Other names: Basfapon ,Unipon

Active: Selective herbicide

Chemical properties: The acid itself is not used directly. Commercial products usually contain 85% sodium salt or mixed sodium and magnesium salts of dalapon.

Toxicity: Acute oral LD 50 970 mg/kg

Signal word Caution: Antidote Treat symptomatically

Handling and Storage Caution

• Do not contaminate water, food or feed by storage or disposed of this product.
• Do not use spray equipment contaminated with this product for any purpose unless thoroughly cleaned with a suitable cleaner.

Applications

• Effective against quack grass , bermuda grass, johnson grasss and other perennial grasses Often it is used as a pre plant treatment to control established perennial grasses in crop land.
• It is translocated to the roots of most SPP and acts as a growth regulator.

Combinations

• Dowpon contains 46.7% dalapon sodium salt + 7.8% dalapon magnesium salt + 30.6% TCA sodium salt Chloropon is a mixture with 2,4-D

Combinations are

Pregloneweedol with diquat
Gramonol---- with monolinuron
Totarcol-----with dexruon
Pathcleer---with diquat and simazine

Glyphosate

Chemical name: N-(phosphonomethyl ) glycine

Common name: Glyphosate

Action: Herbicide

Toxicity: Acute oral LD 50,4300mg/kg

Signal word Caution: Application Shows much promise for the control of johnson grass applied just after harvest of such crops as grain sorghum and cotton. Pre emergence for the control of both perennial and annual weeds as a foliar application.

Molinate

Chemical name: S-Ethyl hexa hydro-1,H-azepine-1,carbo thionate

Common name: Molinate

Former name: Hydrum

Action: Selective herbicide

Toxicity: Acute oral LD 50 (male rat )501---720mg/kg Acute dermal LD50 2000mg/kg Rapidly metabolised.

Signal word Caution: Application Particularly effective for control of water grass in rice.

Formulations: Emulsifiable liquid (8 pounds/gallons) ,Grannules 5%

Combinations: With propanil for use on rice

Amitrole

Chemical name: 3, Amino-1,2,4-triazole

Common name: Amitrole 90,Amizole

Action: Non-selective, translocated

Application: Pre-emergence and post emergence

Uptake & mode of action: The chemical is absorbed by the foliage and roots and readily translocated to the meristematic zones.

Properties:

• Melting point is 153 to154 degree celsius
• Solubility: soluble in water 28 gms/100ml at 23 degree centigrade
• LD50value : 15000mg/kg

Weeds controlled

• Cyanodon dactylon
• Cyperus rotundus
• Typha spp.,
• Setaria spp.