Biology and management of Sacciolepis interrupta (Wild.) Stapf in rice
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Date
2020
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Department of Agronomy, College of Horticulture, Vellanikkara
Abstract
Sacciolepis interrupta is a tropical grass weed which mimics rice crop at early stages of growth and of late has been appearing as a major weed in many rice growing areas. In India, it is reported in rice growing areas of eastern India and Kerala. In Kerala, the occurrence of S. interrupta was earlier confined to semi dry rice cultivation in Palakkad districts however, now it has been reported in wet seeded as well as transplanted rice culture in other parts of the State. Knowledge on biology and ecology of weeds and their interaction with crops play a key role in weed management. The research programme entitled ‘Biology and management of Sacciolepis interrupta (Willd.) Stapf in rice’, included field survey, laboratory, pot culture and field experiments to study the biology, growth, propagation, dormancy and germination requirements of S. interrupta. The study assessed the efficacy of different pre and post-emergence herbicides, individually as well as in an integrated manner, so as to develop an effective recommendation for management of S. interrupta in direct seeded rice. Surveys were conducted twice in the major rice tracts of Kerala viz., Kole, Kuttanad and Palakkad. The results of the survey suggested the probability of S. interrupta becoming a problem weed in rice tracts of Kerala, and attaining the status of a dominant weed like weedy rice. The density and dominance indices clearly indicated the severity of this weed in the surveyed areas. Based on morphological characters of different morphotypes found in the surveyed areas, S. interrupta could be grouped into three groups: A, B and C, which might have evolved as an adaptation to the existing habitat, cultural practices and climatic conditions. Group A (green variegated) refered to morphotypes from Palakkad with medium stature and narrow light green leaves and having green coloured panicles (4-6 nos./plant), oblong spikelets (311-348 spikelets/panicle), and spikelet length and width varying between 4.6-4.8 mm and 0.9-1.3 mm respectively. Group B (purple variegated) from Kole tract, with tall statured plants and narrow dark green leaves,
had purple coloured panicles (4-6 nos./plant), and enlongated spikelets (311-348 spikelets/panicle), with spikelet length of 4.6-4.8 mm and width of about 0.9-1.3 mm. Kuttanad tract types were categorized into Group C (green-purple variegated), which were short statured, profuse tillering plants with broad dark green leaves having bicoloured green and purple panicles (6-8 nos./plant), oblong to bulged spikelets (378-391 spikelets/panicle), and short spikelets with length of 4.1-4.5 mm and width of 1.6-1.8 mm. Sacciolepis interrupta is a C4, grass weed having fibrous root system, and stems were erect or leaning with creeping or geniculate habit. Nodes were glabrous with roots at lower nodes. Leaves were lanceolate; either glabrous or sparsely pilose. The plant height varied from 70 to 112 cm, and inflorescence was an erect, compact, terminal panicle, about 8 to 30 cm long, of either interrupted or spiciform type. The spikelets were ovate or lanceolate, either green or green with violet variegations and about 2.1 to 4.8 mm long. The flowers of S. interrupta were violet or purple or white in colour. The seeds were very small, oval to oblong in shape, light brown to dark brown in colour, and 1000 seed weight varied from 2.2 g to 4.2 g. Germination studies revealed that seeds of S. interrupta were dispersed with high levels of induced dormancy and were able to germinate both in upland as well as flooded conditions. Seed germination was strongly influenced by seasonal variations in temperature and light. Higher temperatures of 330C to 380C with continuous light of 14 hours triggered germination. Seeds placed on soil surface and at 2 cm depth had higher rate of germination and emergence. Seed longevity studies revealed prolonged seed persistence of upto one year. A persistent seed bank due to secondary dormancy favoured the periodic reappearance of species and increase in the soil seed bank. Different methods of propagation i.e., by seeds, culm cuttings and root clumps were observed. High regeneration capacity of different plant parts promoted its survival and spread. Field experiments were conducted in 2017 and 2019 at Chithali, Palakkad in a farmers’ field where the infestation of Sacciolepis was very high. Different pre-
and post-emergence herbicides and integrated methods were tested for management of S. interrupta. The pre-emergence herbicide treatments included oxyflourfen, pretilachlor, pendimethalin, oxadiargyl, stale seedbed for 14 days, hand weeding at 20 and 40 DAS, and unweeded control. Hand weeding was the most efficient method for control of S. interrupta. Stale seedbed was found to give efficient control of the weed by depleting the soil seed bank. Among pre-emergence herbicides, oxyfluorfen @ 0.15 kg/ha and oxadiargyl @ 0.10 kg/ha were found effective, however, weed control lasted only upto 30 DAS. The post-emergence treatments included cyhalofop-butyl, bispyribac sodium, penoxsulam, fenoxaprop–p–ethyl, two commericial pre-mix formulations triafamone + ethoxysulfuron and cyhalofop-butyl+ penoxsulam, hand weeding at 20 and 40 DAS, and unweeded control. Fenoxaprop-p-ethyl @ 0.06 kg/ha and cyhalofop-butyl @ 0.08 kg/ha was found to be better post-emergence herbicides, resulting in improved yield attributes and grain yield of 2299 kg/ha and 1983 kg/ha respectively. Integrated weed management treatments included stale seed bed + fenoxaprop–p–ethyl, stale seed bed + cyhalofop-butyl, stale seed bed + hand weeding, oxyfluorfen + fenoxaprop–p–ethyl, oxyfluorfen + cyhalofop-butyl, oxyfluorfen + hand weeding @ 45 DAS, hand weeding at 20 and 45 DAS and unweeded control. Stale seed bed followed by hand weeding at 45 DAS or pre-emergence application of oxyfluorfen @ 0.15 kg/ha followed by hand weeding at 45 DAS, could be recommended as an integrated method for control of S. interrupta, as these treatments gave significantly higher weed control efficiency and resulted in high grain yields and B:C ratios of 4239 kg/ha and 1.9; 4079 kg/ha and 1.8 respectively.
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PhD