A handbbok on Weed Control in Rice.pdf

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Bensulfuron controls many broadleaf weeds and sedges. It can be applied as preemergence or early postemergence treatment. When used in combination with a grass herbicide such as thiobencarb, molinate, or butachlor, bensulfuron provides excellent weed control. Application can be made up to the 3-leaf stage of the weeds. Bensulfuron provides good control of S. maritimus when applied 6-12 d after emergence of the weed (Bernasor and De Datta 1986). Water solubility at 25 °C is 120 mg/liter. LD 50 in rats is 75,000 mg/kg. LC 50 (96 h) for rainbow trout is >150 mg/liter. Polycyclic alkanoic acids Polycyclic alkanoic acids control grass weeds. In general, polycyclic alkanoic acids are lost from the soil through biodegradation, rather than through leaching or volatilization. Rainfall after foliar application can greatly reduce herbicide absorption because of a reduced amount of herbicide in contact with the plant. One example of the group is fenoxaprop. Herbicides such as MCPA, 2,4-D, and bentazon antagonize polycyclic alkanoic acids. Fenoxaprop. Fenoxaprop (0.03-0.05 kg ai/ha) is a postemergence, selective herbicide for control of annual and perennial grassy weeds. It is a contact herbicide that is partly systemic. Rice is tolerant from the 3-leaf stage to early tillering. Fenoxaprop has no soil activity. It should not be applied with phenoxy compounds. Water solubility at 25 °C is 0.8 mg/liter. LD 50 is 2,357 mg/kg. Miscellaneous herbicides Several herbicides do not clearly fall into any of the groupings. These herbicides differ in chemistry, selectivity, and mode of action. Bentazon, chlomethoxynil, cinmethylin, oxadiazon, and quinclorac are examples. Bentazon. Bentazon (1-2 kg ai/ha) selectively controls a number of broadleaf weeds and sedges, primarily by contact action. Broadleaf weeds at the 2- to 10-leaf stage are controlled most readily. Delay in application will result in inadequate control. In irrigated rice, bentazon should be applied only to weeds that have emerged above the water level. Bentazon does not control grasses and has no known preemergence activity. Available commercial mixtures include bentazon + MCPA and bentazon + propanil. Water solubility is 500 mg/liter. LD 50 for rats is about 1,100 mg/kg. It has low fish toxicity. LC 50 (96 h) for rainbow trout is 510 mg/liter. Chlomethoxynil (chlometoxyfen). Chlomethoxynil is used at 1.5-2.5 kg ai/ha in transplanted and upland rice. It is applied 3-8 d after transplanting rice. Water solubility is 0.3 mg/liter at 15 °C. LD 50 for mice is 3,300 mg/kg. LC 50 (40 h) for carp is 237 mg/liter. Cinmethylin. Cinmethylin provides excellent control of grasses and moderate suppression of broadleaf weeds and sedges. It has been tested at 100-200 g ai/ha for transplanted rice 4-9 d after transplanting and at 100 g ai/ha for direct seeded rice 7-9 d after seeding. Water solubility is 61 mg/liter. LD 50 is 3,900 mg/kg. Oxadiazon. Oxadiazon is a preemergence herbicide applied at 0.5-0.75 kg ai/ha. Uptake by weed seedling shoots causes plant death because root uptake is low. Its postemergence activity against grasses is limited. Because it has low water solubility and high adsorption, oxadiazon is not leached and has good persistence. It can be used in transplanted and direct seeded rice. Commercial mixed formulations include oxadiazon + 2,4-D and oxadiazon + propanil. Oxadiazon can be specifically formulated to be applied directly onto the surface of the ricefield floodwater. A shaker bottle with a calibrated stopper is used to spread oxadiazon directly onto the water without any dilution. The field should be flooded 3-5 cm at application and water should not be disturbed for 2-5 d after application. Water solubility is 0.7 mg/liter at 20 °C. LD 50 for rats is more than 8,000 mg/kg. LC 50 (96 h) for rainbow trout is 1-9 mg/liter; for catfish, ³15.4 mg/liter. Piperophos. Piperophos is a piperidine compound used as a preemergence and postemergence herbicide. It controls annual grasses and sedges. The commercial product containing piperophos + dimethametryn in the ratio 4:l is used in rice to control most annual weeds. It is applied at 1-2 kg ai/ha at the 2- to 4-leaf stage of weed. It has good selectivity in transplanted and upland rice. Principal herbicides 71
Quinclorac. Quinclorac is a chino- line-carboxylic acid compound used as a selective preplant, preemergence, and postemergence herbicide. It has been experimentally tested in rice at 125-300 g ai/ha for grass weed control. Organic matter in the soil will decrease herbicidal activity. Early postemergence application when grass weeds are at the 1- to 3-leaf stage will give the best results. Although results are best when quinclorac is applied onto saturated soil, it can also be applied onto dry soil or into standing water not deeper than 5 cm. Quinclorac can be safely used in dry seeded and water seeded rice when application is made postemergence, from the 1- to 2-leaf stage onward. It may be tank-mixed with other rice herbicides. Oral LD 50 , is 2,610 mg/kg. Differences in herbicide tolerance among rice cultivars Rice cultivars may vary in their tolerance for or susceptibility to herbicides. Broadleaf herbicides are expected to have little effect on rice. The differences in sensitivity to 2,4-D and MCPA (phenoxy acetic acid herbicides) that has been observed is due to differences in the growth stage of the cultivars at the time of herbicide application. 72 Weed control handbook Susceptibility of rice cultivars to grass herbicides has been observed with propanil, butachlor, thiobencarb, pendimethalin, molinate, and piperophos-dimethametryn. For example, IR5, IR28, and IR46 are susceptible to thiobencarb (Shin et a1 1989). Indica varieties are usually more susceptible to simetryn than are japonica varieties. On the other hand, bensulfuron has good crop safety on indica rice varieties but less crop safety on japonica types. Cultivar tolerance may be due to differences in growth rate, growth stage, morphology, physi- ology, and biochemistry. Herbicide selectivity is relative and can be overcome by increasing dosage and by changes in environmental conditions. Herbicide label informa- tion should be followed at all times to prevent severe damage to the rice crop.
Page 1 and 2:
1991 P.O. Box 933, 1099 Manila, Phi
Page 3 and 4:
Foreword Farmers everywhere search
Page 5 and 6:
Contents FOREWORD PREFACE 1 S IGNIF
Page 7 and 8:
Table 1.3. Weeds as secondary hosts
Page 9 and 10:
horizontal leaves. Tall plants have
Page 11 and 12:
Chapter 2 Rice weeds of worldwide i
Page 13 and 14:
Lowland rice weeds ASTERACEAE (Comp
Page 15 and 16:
Lowland rice weeds / CYPERACEAE (se
Page 17 and 18:
Lowland rice weeds / CYPERACEAE (se
Page 19 and 20:
Lowland rice weeds / ONAGRACEAE (ev
Page 21 and 22: Mature plant Inflorescence Seed, ma
Page 23 and 24: Lowland rice weeds/POACEAE (grass f
Page 25 and 26: Lowland rice weeds / POACEAE (grass
Page 27 and 28: Lowland rice weeds / PONTEDERIACEAE
Page 29 and 30: Upland rice weeds AIZOACEAE (carpet
Page 31 and 32: Upland rice weeds / ASTERACEAE (sun
Page 33 and 34: Upland rice weeds / CYPERACEAE (sed
Page 35 and 36: Upland rice weeds / POACEAE (grass
Page 41 and 42: Upland rice weeds / PORTULACACEAE (
Page 43 and 44: Deepwater weeds / CONVOLVULACEAE (m
Page 45 and 46: Wetland tillage is common in most t
Page 47 and 48: leaf size), with the resultant shad
Page 49 and 50: Economics of control The economic b
Page 51 and 52: Chapter 4 Principles of herbicide u
Page 53 and 54: Preemergence herbicide application
Page 55 and 56: and behavior in the crop environmen
Page 57 and 58: Table 4.1. Meanings of signal words
Page 59 and 60: 4.3 Controlled-droplet applicators
Page 61 and 62: amount after spraying is 8 liters,
Page 63 and 64: The decision to spray should be mad
Page 65 and 66: farmers, however, should wear cloth
Page 67 and 68: Table 5.1. Susceptibilitles a of im
Page 69 and 70: Propanil can be used at 3-4 kg ai/h
Page 71: Thiocarbamates Thiocarbamates are a
Page 75 and 76: Planting method Transplanting into
Page 77 and 78: Direct seeded on puddled soil In di
Page 79 and 80: Table 6.2. Herbicides suitable for
Page 81 and 82: 6.4 Rice growth stages when herbici
Page 83 and 84: Fertilizer Incorporating N and P fe
Page 85 and 86: Nurseries Seedling nurseries should
Page 87 and 88: Land preparation Leveling the puddl
Page 89 and 90: Land preparation Land preparation s
Page 91 and 92: Chapter 8 Weed control in upland ri
Page 93 and 94: Hand weeding The weed-free period r
Page 95 and 96: Chapter 9 Weed control in deepwater
Page 97 and 98: Hand weeding Hand weeding is the mo
Page 99 and 100: Chapter 10 Management of some diffi
Page 101 and 102: Wild rices The important wild rices
Page 103 and 104: Herbicides For effective control of
Page 105 and 106: IRRI-International Rice Research In
Page 107 and 108: B. Conversion table for granular fo
Page 109 and 110: Index A Absorption of herbicide, 50
Page 111 and 112: in deepwater and floating rice, 96
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