Integration of Thymol, Soil Improvers and Biostimulants for Management of Tomato Pests, Diseases, Nematodes and Rhizosphere Microbial Dynamics Kirinyaga County, Kenya
Wafula, Geoffrey Ongoya
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Soil-borne pathogens, root knot nematodes and insect pests remain a major constraint to tomato Solanum lycopersicum L. (Solanales; Solanaceae) production in Kenya. The study was carried out with an aim of evaluating the effect of integrating selected plant essential oils, soil improvers and bio-stimulants on rhizosphere microbial, soil-borne pathogens, nematodes and insect pests of tomato. The plant essential oil used (treatments) in this study were thyme oil, bio-stimulants (Trichoderma harzianum), sea weed (Ascophyllum nodosum and Fucus vesiculosus), a sea weed with humic acids, a sea weed with amino acids, peptides and an amino acid; while the soil improver was based on pellets of plant-based raw materials and seaweeds containing 7.5% N in pure vegetable form, soft ground potassium sulphate with magnesium (4% K2O) and soft ground rock phosphate (2% P2O5). The study was conducted in farmer fields in Kimbimbi and Kagio in Kirinyaga County from September 2016 to July 2017 and in the greenhouse at Kenyatta University from February to October 2018. Data collection was carried out on soil-borne diseases, insect pest population and diversity, plant growth and yield parameters. It was subjected to ANOVA using Genstat statistical packages and means were separated using Fisher’s Least Significant Difference (LSD) at P≤0.05. The results indicated that thyme oil was effective in suppressing the fusarium wilt and early blight by between 49.2% to 65.9% and 58.9% to 84.8%, respectively. Plant essential oils were effective in the management of thrips (mainly Frankliniella occidentalis) and whitefly (Mainly Bemisia tabaci and Trialeurodes vaporariorum) infestations causing a reduction in infestation of between 47% to 68.6 % and 41.3% to 66.2%, respectively. The application of the soil improver had a positive effect on the microbial population of fungi resulting in an increase of active fungi at the soil rhizosphere of tomato plants of up to 292%. Application of T. harzianum was effective in the management of Fusarium wilt (39.6% to 48.6% reduction) and root knot nematodes (48.8% to 60.9% reduction). The integration of thyme oil, soil improver, T. harzianum and bio-stimulants was effective in the management of a reduction of up to 66.9% for Fusarium Wilt, 83.4% for early blight, 60% for root knot nematodes, 66% for thrips and 47.3% for whitefly as well as increasing yield of tomato by up to 125.6%. Based on these results, the integration of thyme oils, Trichoderma harzianum and bio-stimulants can be recommended for management of, fusarium wilt, early blight, root knot nematodes, thrips and whitefly in tomato production.