A handbbok on Weed Control in Rice.pdf

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Weed control after flooding Weed control after flooding in deep water and floating rice is mainly done by hand. Farmers in some areas grow a strip of Sesbania aculeata or Aeschynomene aspera along the borders of deepwater and floating ricefields to provide a barrier against the entry of E. crassipes and other weeds into the fields. Barricades of bamboo poles and bars are sometimes installed. Hand weeding Attempts to weed deepwater and floating rice from boats-a difficult task-have been made in cases of severe weed infestation. In Mali, farmers hand weed after flooding to minimize competition from O. longistaminata and O. barthii. Perennial E. stagnina is also removed by hand. Herbicides Herbicides are effective in deepwater and floating rice only before flooding. 98 Weed control handbook
Chapter 10 Management of some difficult weeds in rice Many weeds can be controlled effectively only by using a combination of methods. Using only one weed control method leads to a buildup of weed problems. This chapter gives informa- tion on how intractable rice weeds can be managed through an integrated approach. Scirpus maritimus Scirpus maritimus, a perennial sedge that spreads by tubers, is widespread in lowland rice in several countries in Asia, Europe, and temperate climate USA (see page 000). S. maritimus is a very competitive weed: it produces numerous tubers, has fast shoot growth, is able to emerge through fields with standing water, and has rapid nutrient uptake. Season-long competition from S. maritimus can reduce rice yields 60-100%. Its tubers and buds can remain dormant in the soil, making this weed difficult to eradicate. S. maritimus is most competitive from its early growth stages to 80 d after germination. The S. maritimus -free period required in rice is the first 4 wk. Cultural control Cultural control of S. maritimus involves tillage, crop rotation, and water management. Depth and type of primary cultivation greatly affect the S. maritimus population. Shallow cultivation and zero tillage encourage emergence of tubers retained on the soil surface, resulting in rapid population buildup. Deep plowing buries the tubers and results in growth of fewer seedlings. The practice of zero tillage leads to the buildup of a S. maritimus population, but minimum tillage can be as effective as conventional tillage in limiting its growth. The weed persists under continuously wet conditions but diminishes dramatically with time under continuously dry conditions. A year of rotation of an upland crop with lowland rice will reduce the preva- lence of S. maritimus. Hand weeding Hand weeding is effective in control- ling S. maritimus. The rice crop should be kept weed-free for at least the first 4 wk. This makes several hand weed- ings necessary, because S. maritimus tubers germinate within 5 d after harrowing and grow rapidly. Herbicides Herbicides effective against S. maritimus in transplanted and direct seeded flooded rice include bentazon, fenoxaprop, propanil, 2,4-D, and bensulfuron. 2,4-D at 0.5 kg ai/ha is best applied when S. maritimus has 6-8 leaves. 2,4-D applied preemergence does not control the weed, although it may reduce the stand of annual grasses. Bentazon at 1-2 kg ai/ha should be applied at the 6- to 8-leaf stage (about 25 d after sowing [DASI). Bensulfuron at 50 g ai/ ha applied at 6-8 DAS or DT (2- to 3-leaf stage of the weed) effectively controls S. maritimus and annual weeds. Integrated control Integration of all workable weed control practices can provide effective and economical control of S. maritimus. Such integration should begin by creating an environment favorable to rice growth but unfavorable to weed growth. This includes using well- adapted, high-yielding rice cultivars; appropriate fertilizers; good management; and crop rotation. Weed control efficiency is improved by integrating the use of herbicides and hand weeding. The rotational crops used depend on the region; maize, sorghum, and soybean are becoming increasingly important. Difficult weeds 99
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1991 P.O. Box 933, 1099 Manila, Phi
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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
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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
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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
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Upland rice weeds / POACEAE (grass
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Page 41 and 42:
Upland rice weeds / PORTULACACEAE (
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Deepwater weeds / CONVOLVULACEAE (m
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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 and 94: Hand weeding The weed-free period r
Page 95 and 96: Chapter 9 Weed control in deepwater
Page 97: Hand weeding Hand weeding is the mo
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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