Biology and management of goose weed (Sphenoclea zeylanica Gaertner) in wetland rice

Abstract

An investigation entitled ‘Biology and management of goose weed (Sphenoclea zeylanica Gaertner) in wetland rice’ was conducted at College of Agriculture, Vellayani during 2018-2020. The major objectives were to study the biology of the weed, its allelopathic effect on crop and also to develop an effective and economic management strategy using herbicides in wet seeded rice. The field experiment was undertaken at IFSRS, Karamana during kharif 2019. Weed biology was studied by observing randomly selected sample plants in weedy check plots starting from the emergence of the weed. The field experiment was laid out in randomized block design with eight treatments and three replications. The weed control treatments included T1: bensulfuron methyl + pretilachlor @ 60+600 g ha-1 at 5 days after sowing(DAS), T2: pyrazosulfuron ethyl @ 25g ha-1 at 5 DAS, T3: bispyribac sodium @ 25 g ha-1 at 15-20 DAS, T4 :penoxsulam + cyhalofop butyl 6% OD at 150 g ha-1 at 20 DAS, T5: metsulfuron methyl + chlorimuron ethyl @ 4g ha-1 at 20 DAS, T6: ethoxysulfuron @ 15 g ha-1 at 20 DAS, T7 : hand weeding at 20 and 40 DAS, T8 : weedy check ( unweeded control) and the treatments T1 to T6 were followed by hand weeding at 35-40 DAS. The lab experiment on allelopathic effect of goose weed on germination and growth of rice seedlings was evaluated with treatments T1: Fresh leaves aqueous extract 10%, T2: Dry leaves aqueous extract 10%, T3: Fresh stem aqueous extract 10%, T4: Dry stem aqueous extract 10%, T5: Fresh inflorescence aqueous extract 10%, T6: Dry inflorescence aqueous extract 10%, T7: Fresh whole plant aqueous extract before flowering 10%, T8: Fresh whole plant aqueous extract after flowering 10%, T9: Distilled water (control). The data on weed biology identified goose weed as an annual. The weed seeds took 3-7 days for germination, 15 days for flowering and 36 days for first spike maturity with an average duration of 69 days in wet seeded rice fields. The weed was observed to propagate by seeds with enormous seed production potential. The average dry matter produced per plant and total dry matter production were to the tune of 26.24 g per plant and 3.75 t ha-1 respectively in the weedy check. The weed was analysed to contain 1.306, 0.087 and 1.695 per cent N, P and K respectively. In the field experiment, Sphenoclea zeylanica was the dominant weed flora during all the growth stages of the crop. Initially, a lower weed density was recorded in T1, but taken over by T4 at 30, 45 and 60 DAS. The weed dry weight was the lowest in T1 at 15 and 30 DAS (0.08 and 6.41 g m-2), whereas at 45 and 60 DAS, T4 recorded the lowest values (1.35 and 4.61 g m-2). T1 registered lesser relative weed density of S. zeylanica up to one month and later by T4. Unweeded plot showed dominance of the weed over other flora with a relative density of 70.33 per cent. Though weed control efficiency was higher in T1 upto 30 DAS (99.28 and 96.22 per cent), T4 recorded higher values during critical stages of crop growth at 45 and 60 DAS (99.54 and 98.85 per cent). T4, T1 and T5 recorded minimum NPK removal and to be precise only one tenth of N removal registered in weedy check in comparison to others due to lower weed dry matter accumulation Among the weed management practices tested, T1 recorded higher plant height at 30, 60 DAS and at harvest. Both T1 and T4 recorded higher yield and yield attributes like number of panicles m-2(320 and 308.3), number of grains panicle-1 (173 and 177), grain yield (5461 and 5355 kg ha-1) and straw yield (7710 and 7646 kg ha-1). Bensulfuron methyl + pretilachlor @ 60+600 g ha-1 at 5 DAS followed by hand weeding at 35-40 DAS turned out to be the most economic weed management practice with a higher B: C ratio of 1.83. This was followed by penoxsulam + cyhalofop butyl 6% OD at 150 g ha-1 at 20 DAS followed by hand weeding at 35-40 DAS with a B: C ratio of 1.77. Higher nutrient uptake by the crop was noticed in bensulfuron methyl + pretilachlor (T1), T4 and T5 due to higher dry matter production. The extent of yield reduction due to presence of weeds in wet seeded rice was estimated to be 57 per cent. The study on allelopathic influence of goose weed revealed strong inhibitory influence for its dry leaves and dry inflorescence on germination percentage (92.67 and 80%) and dry weight (96.98 and 96.12%) of rice seedlings. Shoot length, root length, fresh weight, dry weight and vigour index were also recorded the lowest in T2 and T6. From the results of the study, it could be concluded that Sphenoclea zeylanica could become a serious weed in wetland rice fields being a prolific seed producer with high dry matter production. Application of bensulfuron methyl + pretilachlor @ 60+600 g ha-1at 5 DAS followed by hand weeding at 35-40 DAS was found to be the most effective and economic management strategy. The inference of allelopathic studies indicated that dry leaves and inflorescence of goose weed have strong inhibitory influence affecting germination and growth of rice.