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Seaweeds as alternative to chemical pesticides for the management of root diseases of sunflower and tomato
With the rising popularity of organic farming, due to adverse effect of chemicals, the seaweed fertilizer industry is growing rapidly worldwide. Seaweeds act as natural plant growth stimulator and enable the plants to withstand drought, disease or frost. Root diseases of tomato and sunflower caused by root rotting fungi, Fusarium spp., Rhizoctonia solani and Macrophomina phaseolina, and root knot nematode, Meloidogyne spp., are the major constraints in tomato and sunflower production. In our studies, ethanol and water extracts of several seaweeds showed significant nematicidal activity against Meloidogyne javanica. In this study, efficacy of three seaweeds Spatoglossum variabile, Melanothamnus afaqhusainii and Halimeda tuna was compared with a fungicide Topsin-M and a nematicide carbofuran both in screen house and under field condition. Seaweed and pesticides showed more or similar suppressive effect on root pathogens of tomato and sunflower by reducing fungal root infection and nematode's galls on roots and nematode's penetration in roots. However, mixed application of S. variabile with carbofuran caused maximum reduction in nematode's penetration in roots and produced greater fresh shoot weight, root length and maximum yield of tomato under field condition. Seaweeds offer a non-chemical means of disease control, which would also protect our environment from the use of hazardous chemicals.