A handbbok on Weed Control in Rice.pdf

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Herbicides Chemical weed control in upland rice is economical and effective under certain conditions. It may be the only weed control method feasible for large-scale rice farms. Herbicides can complement other weed control methods or can be used in combina- tion with hand weeding to give acceptable weed control. For optimum effectiveness of preemergence herbicides, which require moist or wet soil, timely rains after application are essential. When residual herbicides are applied to soils that have remained dry for a long time, they give variable results. The persis- tence of many preemergence herbicides is so short, they cannot control successive flushes of weed seedlings. This makes follow-up hand weeding or application of a postemergence herbicide necessary. Among the preemergence herbicides, butachlor, oxadiazon, dinitramine, pendimethalin, thiobencarb, fluorodifen, and piperophos-dimethametryn have been widely tested. Postemergence herbicides such as propanil and MCPA are also effective. Herbicide combinations are often more effective than a single herbicide. Applying a preemergence herbicide such as oxadiazon, butachlor, or thiobencarb, followed by propanil 15-25 d later will provide better weed control than will any of these herbicides applied alone. Early postemergence application of a postemergence herbicide (eg, propanil) combined with a residual herbicide, done at the time the postemergence herbicide is most effective, has the advantages of providing season-long control and saving time and labor by combining two spraying operations. Table 8.1 and Figure 8.1 provide information on common herbicides that may be used in upland rice. 94 Weed control handbook Table 8.1. Herbicides suitable for use in upland rice. Herbicide Bentazon Bifenox Butachlor Butralin 2,4-D or MCPA Dinitramine Fluorodifen Oxadiazon Oxyfluorfen Pendimethalin Piperophos + dimethametryn Propanil Thiobencarb Rate (kg ai/ha) 1.0-2.0 2.0 2.0 2.0 0.5 1.5 2.5-4.0 0.75-1.5 0.35 2.0 1.0-2.0 3.0-6.0 3.0 Comments and source of information Selective postemergence control of certain broadleaf weeds and sedges (IRRI 1982). Does not control grasses. Apply postemergence when weeds are at the 4- to 10-leaf stages. Delayed application allows the weeds to exceed maximum size, resulting in inadequate control. Apply preemergence from seeding to early spikelet stage. Apply to moist soils for best results. Bifenox + propanil can be applied postemergence when rice has 2-3 leaves and weeds are 2.5 cm high (Akobundu 1987). Effective against grasses and broadleaf weeds; less effective against perennial sedges (IRRI 1975). Apply preemergence to control annual grasses (IRRI 1976). Apply as postemergence spray after tiller initiation, about 21-30 d after seeding (DAS) (Dixit and Singh 1981). Apply preemergence (IRRI 1978). Apply 0-3 DAS for residual preemergence control of annual grasses (De Datta 1972). Apply preemergence 0-2 DAS. Rice growth depression has been observed 15-20 d after emergence (IRRI 1975). Apply preemergence. May be moderately toxic to rice (IRRI 1983). Apply preemergence or early postemergence, combined with propanil (IRRI 1975). Excellent for control of Rottboellia cochinchinensis. Apply 4-6 DAS (Dubey et al 1980). Apply at 2- to 3-leaf stages of grass. High temperatures increase contact burn and may injure rice (IRRI 1980). Apply before 2-leaf stage of weeds and after 1-leaf stage of rice (IRRI 1988a).
Chapter 9 Weed control in deepwater and floating rice Deepwater and floating rice constitute about 11% of the world’s rice area (IRRI 1988b). They are grown in the deltas, estuaries, and river valleys of Bangladesh, Cambodia, India, Indonesia, Myanmar, Thailand, and Vietnam. In Africa, deepwater and floating rice-growing areas are found in the inland Niger River delta in Mali, in the Niger River delta, Nigeria, and in inland swamps. Deepwater and floating rice cultures Deepwater rice is grown in areas where the maximum depth of stand- ing water exceeds 50 cm for a signifi- cant period of rice growth. Where water depth is greater than 100 cm, the culture is referred to as floating rice or very deep water rice. Fields are not bunded and flooding usually occurs only during the later part of the growing season. Rice may grow under drought conditions for 40-60 d before flooding occurs. Weed problems Weeds are a major problem in deepwater and floating rice because rice normally is seeded into soils that may remain dry for 6-12 wk. Fields may also be flash flooded. The dry soil and intermittent flash flooding result in a broad spectrum of weeds-from upland to semiaquatic and aquatic- that successively compete with the rice crop. Weeds adapted to dryland compete at early crop stages, die upon flooding, and are succeeded by aquatic weeds. Before flooding, deepwater and floating rice may be infested by Echinochloa colona, Eleusine indica, Cyperus rotundus, C. iria, and C. difformis. These weeds also may compete with rice during the early stages of flooding. Deepwater and floating rice may suffer severe weed infestations during the preflood period. Weed problems are often aggravated by poor stand establishment due to drought. At the preflood stage, weeds reduce growth and tillering of rice plants and can reduce grain yield as much as 33% (De Datta and Hoque 1982). Total crop loss can occur if flooding is below normal. Minimizing competition from weeds at early rice growth stages largely determines how well deepwater and floating rice will tolerate stresses caused by flooding at later stages. Aquatic weeds that occur upon flooding are less a problem when stand establishment is good and rice tillering is adequate than when early weed competition is severe. In small cropping areas where farmers wet seed or transplant deepwater rice, puddling reduces weed infestation. Amphibious weeds, such as the wild rices, Scirpus sp., Sesbania sp., and Leersia hexandra, can compete with rice under dryland or flooded conditions. Eichhornia crassipes, Ipomoea aquatica, Monochoria vaginalis, and Pistia stratiotes are found in deepwater rice after flooding has occurred. Weeds such as the wild rices possess flood tolerance and elongation ability, and grow with rice in rising floodwater. Therefore, they are able to cause considerable yield losses. Masses of E. crassipes are usually introduced to the ricefield by water currents or strong winds. When this occurs, E. crassipes can completely smother the rice crop within a few days. In West Africa, the most troublesome weeds include E. stagnina and E. pyramidalis, and the wild rices Oryza longistaminata and O. barthii. Weed control before flooding The deepwater rice cycle has two distinct phases—before flooding and after flooding. Weed control methods can be described best within these phases. Deepwater rice before flooding is treated either as rainfed lowland rice or as upland rice, using the same weed control methods. Deepwater and floating rice 95
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1991 P.O. Box 933, 1099 Manila, Phi
Page 3 and 4:
Foreword Farmers everywhere search
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Contents FOREWORD PREFACE 1 S IGNIF
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Table 1.3. Weeds as secondary hosts
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horizontal leaves. Tall plants have
Page 11 and 12:
Chapter 2 Rice weeds of worldwide i
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Lowland rice weeds ASTERACEAE (Comp
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Lowland rice weeds / CYPERACEAE (se
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Lowland rice weeds / CYPERACEAE (se
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Lowland rice weeds / ONAGRACEAE (ev
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Mature plant Inflorescence Seed, ma
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Lowland rice weeds/POACEAE (grass f
Page 25 and 26:
Lowland rice weeds / POACEAE (grass
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Lowland rice weeds / PONTEDERIACEAE
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Upland rice weeds AIZOACEAE (carpet
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Upland rice weeds / ASTERACEAE (sun
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Upland rice weeds / CYPERACEAE (sed
Page 35 and 36:
Upland rice weeds / POACEAE (grass
Page 37 and 38:
Page 39 and 40:
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 and 72: Thiocarbamates Thiocarbamates are a
Page 73 and 74: Quinclorac. Quinclorac is a chino-
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: Hand weeding The weed-free period r
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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