A handbbok on Weed Control in Rice.pdf

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Reducing weeds in dry seeded rice culture is possible by practicing a stale seedbed. After land preparation, weeds are allowed to emerge follow- ing rain or irrigation, then destroyed by shallow cultivation or application of a nonresidual contact herbicide. The herbicide should be applied or cultivation done when most of the weeds have reached the 2- to 5-leaf stage. Rice is then seeded into the weed-free field. Planting method Rice seeds are broadcast seeded into dry or moist soil and covered by harrowing, or drilled 3-5 cm deep into the soil. High seeding rates can suppress weeds, but the cost of seeds should be considered against other direct control measures available because there is no yield advantage in increasing seed rates above 100 kg/ha. Cultivar Both short- and intermediate-statured cultivars are used for rice broadcast or drilled into dry soil. For broadcast seeded rice, the cultivar used should be stiff-strawed to avoid severe lodging. Water management Good water management is important in controlling weeds in broadcast or drill seeded flooded rice. After dry seeding, the soil may be intermittently flooded and drained to allow for rice emergence. The water level is then increased gradually for a few weeks until a continuous flood of 5-cm depth is maintained. Table 6.3 Herbicides suitable for use in broadcast or drill seeded, dry-sown irrigated rice. Herbicide Bentazon Butachlor Butralin 2,4-D or MCPA Molinate Oxadiazon Pendimethalin Piperophos + dimethametryn Propanil Thiobencarb Rate (kg ai/ha) 2.0 1.5-2.0 2.0 0.5-1.0 3.0-5.0 0.75-1.0 2.0 0.75-1.25 3.0-4.0 3.0 Hand weeding Interrow mechanical weeding is not possible in broadcast seeded rice. Even when seeds are drilled, the interrow spacing is so narrow that only hand or hoe weeding is possible. In this rice culture, two to three-timely hand weedings are sufficient to ensure optimum yields. The soil disturbance involved, however, can cause as much damage to rice as to weeds. The first weeding may be done between 14 and 21 d, depending on weed growth, followed by subsequent weedings when necessary. Comments and source of information Apply as a postemergence herbicide to control broadleaf weeds and sedges. Apply when weeds have germinated but are still small. Water level may be lowered to expose weeds 24 h. Raise water level after treatment (COPR 1976). Apply as preemergence spray 0-3 d after sowing (DAS) to control annual grasses and sedges (IRRI 1977). Apply as preemergence spray 2-3 DAS to control annual grasses (IRRI 1977). Apply 3-4 wk after seeding to control annual broadleaf weeds and sedges (COPR 1976). Apply from presowing to early postemergence to control grassy weeds (Smith 1971). Preemergence application should be 2-3 DAS (IRRI 1977). Apply at preemergence of rice (IRRI 1977). Apply early postemergence to control annual weeds (Green and Ebner 1972). Apply postemergence at the 2- to 3-leaf stages to control grasses and broadleaf weeds (COPR 1976). Apply preemergence immediately after covering the seeds with soil but before the first irrigation or ram. Irrigate 3-5 d after application (IRRI 1979). Herbicides The effects of herbicides are similar for broadcast seeded or drilled dry-sown rice and wet-sown flooded rice. Because of water management problems and difficulties in hand weeding, herbicides are particularly important in this rice culture. Covering the seeds with soil after drill or broadcast seeding increases the tolerance of rice for herbicides but decreases a rice seedling’s flooding tolerance. Butachlor, molinate, oxadiazon, propanil, and thiobencarb are used as Irrigated rice 79
6.4 Rice growth stages when herbicides can be applied in dry-seeded irrigated rice. Bars (–) show periods during which a particular herbicide is applied. *Timing of herbicide application is based on weed emergence and growth stage within the rice growth stage. preplant, preemergence, postemergence, or postflood treatment. Propanil is widely used as a postemergence herbicide, either in addition to or in place of a preemergence treatment. Preplanting herbi- cidal treatments, such as with glyphosate, may also control perennial weeds. Table 6.3 and Figure 6.4 outline the common herbicides and their times of application for this culture. 80 Weed control handbook Water seeded Water seeding of rice is practiced in several parts of Asia, including India, Sri Lanka, Malaysia, and Thailand. It is widely practiced in the USA, southern Europe, USSR, and Australia. Pregerminated rice is broadcast directly onto the flooded field. The rice, which is seeded into water 7-10 cm deep, sinks to the soil, germinates, and emerges from the water. The field remains flooded at a depth of 7-10 cm until a few weeks before maturity. In the USA, seeding into continuously flooded fields began in the 1930s as a cultural method to control E. crus-galli and later as part of a program to control red rice. Weed problems Many weeds and rice will germinate through either soil or water, but not through both. Water seeding takes advantage of that by establishing an early water covering to suppress weeds. Continuous flooding in water seeded rice culture, however, encour- ages aquatic weeds. Where continuous flooding is not maintained, many semiaquatic weeds typical of discontinuously flooded, dry seeded fields can be found in water seeded ricefields. Under such conditions. E. crus-galli, Lepfochloa sp., Aeschynomene virginica, and Sesbania exaltata are weed problems.
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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
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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
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Lowland rice weeds / CYPERACEAE (se
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Lowland rice weeds / CYPERACEAE (se
Page 19 and 20:
Lowland rice weeds / ONAGRACEAE (ev
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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 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: Table 6.2. Herbicides suitable for
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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A handbbok on Weed Control in Rice.pdf

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