Integrated management of fusarium wilt of tomatoes using fungicides, organic matter and neem extract
Mugo, Dishon Njiru
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Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici (F. o. l.) is a major tomato production constraint in Kirinyaga district. This study was carried out to investigate the use of organic soil amendments and fungicides/biopesticides singly or in combination for the management of Fusarium wilt. The most popular tomato varieties in the region; Rio Grande, Onyx and Cal J were used. The varieties have high productivity, marketability and good keeping qualities. Wilting disease symptom was recorded by all the farmers interviewed. Five isolates of F. o. l; isolate 5, 6, 8, 9 and 11 were compared for their infection abilities on Rio Grande, Onyx and Cal J. Findings from greenhouse indicated that there was no significant difference ((P > 0.05) in Fusarium wilt percentage incidences on tomato plants as a result of infection by various isolates. However, a higher percentage incidence was recorded in tomato plants infected with isolate 6. Isolate 6 was more infective on Cal J (% incidence 85.00) than on Onyx (62.50%) and Rio Grande (36.00%). Three fungicides; Milraz, Ridomil and Ortiva were used in in vitro experiments to determine their inhibition abilities on hyphal growth. Higher inhibition on fungal hyphal growth was recorded in media treated with Ridomil (Mean diameter 26.24 ± 4.14 mm). Hyphae on media incorporated with Ortiva had bigger diameter (37.22 ± 5.12 mm) than Milraz (32.18 ± 4.77) but not significantly different. This finding therefore indicated that, Ridomil highly inhibited Fusarium hyphal growth compared to Milraz and Ortiva. A comparison in different rates of Neem Kernel Cake Powder (NKCP) showed that lower disease incidence (42.5 ± 19.8% ) and severity (34.3 ± 15.2% ) were recorded in plants in pots amended with 10 g NKCP than in pots treated with lower rates of 9 g, 7 g, 5 g and 3 g NKCP. Plants in pots treated with 3 g NKCP had the highest percentage disease incidence (67.5 ± 23.1) and severity (43.2 ± 20.5). Stem diameter and plant heights of the Fusarium wilt infected plants treated with 9 g and 10 g Neem extract were bigger than the rest of the treatment although the difference was not significant (p > 0.05). Findings from this experiment showed that, the most effective rate of the Neem cake powder was 10 g/pot. Plants grown in pots treated with “Fungicides + Neem cake powder +Organic matter” had lower disease incidences (mean 40.5%) than those grown in pots treated with other combinations of Fungicides, Neem cake powder and Organic matter. However, the differences in the disease incidences were not significant (P >0.05). Stem diameters and plant heights recorded from different treatments followed a similar trend although there was no significant difference (P>0.05). It was noted that taller plants had the biggest stem diameters, showing a significant relationship between the plant heights and the stem diameters (r = 0.833, P = 0.000). From the results of the study, the use of integrated approach was more effective than single methods in the management of Fusarium wilt of tomatoes. The farmers are therefore advised to use a combination of methods in order to effectively control the disease and improve crop performance.