A handbbok on Weed Control in Rice.pdf

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Land preparation Land preparation for dry seeded deepwater and floating rice is similar to that for upland rice. At planting, the seed bed should be weed free. Deep plowing and harrowing are recommended in the dry season if rhizo- matous perennials are a problem. Many deepwater and floating rice soils have a high clay content, and, the only time to plow them is often when they are dry and very hard. Cultivation must start early because the crop, which draws first on residual moisture and moisture from occasional show- ers, must reach the stage where it can elongate before flooding starts. The stale seedbed technique can be used to reduce weed problems, particularly infestation by wild rices. Planting method Broadcast seeding rice into dry soil is common in deepwater and floating rices. Transplanting or broadcasting pregerminated seeds into puddled soil is also practiced in some areas. If early flash floods occur, however, transplanting involves a greater risk of crop failure than does broadcast seeding. The rice seedling grows as an upland crop for 4-20 wk before flooding occurs. As the floodwaters rise, deepwater rice plants elongate to as tall as 6 m and form a dense mat on the water surface. Cultivar Rice cultivars with elongation ability, photoperiod sensitivity, drought tolerance at the seedling stage, and tolerance for stagnant water conditions at later growth stages are ideal for deepwater and floating rice. 96 Weed control handbook Table 9.1. Herbicides suitable for use in deepwater and floating rice. Herbicide Rate (kg ai/ha) Bentazon 2.0 Butachlor Butralin 2,4-D or MCPA Fluorodifen Oxadiazon Piperophos + dimethametryn Propanil Thiobencarb 1.0-2.0 2.0 0.5 2.5-4.0 0.75-1.0 1.0-2.0 3.0 2.0-4.0 Plant population Because of poor stand establishment, seeding rates tend to be high- 80-200 kg/ha. The crop produces nodal tillers at low plant densities, however, and a high seeding rate does not necessarily increase final grain yield. Nevertheless, the high seeding rate is a good agronomic practice because a high plant population allows rice to develop a canopy that suppresses weed growth. Crop rotations can help control or prevent the buildup of difficult-to- control weeds. In Bangladesh, farmers on the higher ridges of deepwater rice areas grow a crop of jute after one or more deepwater rice crops. The jute crop suppresses wild rice and other weeds. Comments and source of information Selective control of certain broadleaf weeds and sedges. Does not control grasses. Apply postemergence early, when weeds are at the 4- to 10-leaf stages. Delayed application allows weeds to exceed maximum size and results in inadequate control (COPR 1976). Effective against grasses and broadleaf weeds. Less effective against perennial sedges (COPR 1976). Apply preemergence to control annual grasses (COPR 1976). Apply as postemergence spray after rice tillering, 21-30 d after seeding (DAS) (COPR 1976). Apply preemergence 0-3 DAS to control residual annual grasses (COPR 1976). Apply 6-8 d after application (COPR 1976). Apply 4-6 DAS (COPR 1976). Apply at 2- to 3-leaf stages of grass (IRRI 1980). Apply before 2-leaf stage of weeds and after 1-leaf stage of rice (COPR 1976). Fertilizer Deposits of the silt carried by rivers during their annual floods provide high fertility for most deepwater and floating rice soils. The high soil fertility improves stand establishment and elongation ability of rice, but weeds also grow quickly and compete aggressively for nutrients, moisture, and light. Weeds must be controlled to maximize the nutrient uptake efficiency of the rice crop.
Hand weeding Hand weeding is the most effective weed control method in deepwater and floating rice. Weeding should be done 15-25 d after planting. Two to three hand weedings may be neces- sary, depending on the time of flooding. Weeds germinate earlier and grow more vigorously than rice during the preflood period. Mechanical weeding, combined with hand weeding for weed removal within the rows, may be effective when rice is row-seeded. Herbicides Most common weeds present before flooding can be controlled by the herbicides recommended for upland rice. Butachlor, oxadiazon, pendimethalin, thiobencarb, piperophos-dimethametryn, and oxyfluorfen are effective when applied preemergence. Postemergence herbicides such as propanil, 2-4D, and MCPA are also effective in controlling weeds such as I. aquatica. Residual herbicides give variable results when applied to dry soils or when flash floods occur soon after application. Glyphosate can be 9.1 Rice growth stages when herbicides can be applied on deepwater and floating rice. Bars (—) show periods when a particular herbicide can be applied. *Timing of herbicide application is based on weed emergence and growth stage within the rice growth stage. used to control O. longistaminata during fallow. Table 9.1 and Figure 9.1 provide information on herbicides and their appropriate times of application. Deepwater and floating rice 97
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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
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 and 94: Hand weeding The weed-free period r
Page 95: Chapter 9 Weed control in deepwater
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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A handbbok on Weed Control in Rice.pdf

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