EFFECTS OF SOME FUNGICIDE ON INCIDENCE AND SEVERITY OF LEAF BLIGHT AND FRUIT ROT DISEASES OFCUCUMBER

Abstract

ABSTRACT Cucumber (Cucumis sativus L.) is a widely consumed fruit vegetable popular for its nutritional, economic, and health benefits. In Nigeria, its production is significantly threatened by Leaf Blight (LB) and Fruit Rot (FR) fungal diseases, causing yield losses of 60% to 76%, when not controlled. This study therefore evaluated the effects of three fungicides; FS (Five Star (Azoxystrobin 200 g/L + Difenoconazole 125 g/L SC), DF (Dew Force (Pyraclostrobin 40 g/L + Dithomethorm 72 g/L EC), and RG (Ridomil Gold (Metalaxyl 40 g/kg + Mancozeb 640 g/kg) for the management of incidence and severity of LB and FR diseases on two cucumber varieties, Amarsia Super F1 and Oliver Bold F1. The experiment was conducted during the 2023 and 2024 late and early planting seasons respectively, at the Federal University of Agriculture, Abeokuta. Treatments were arranged in a split-plot fitted into Randomized Complete Block Design with three replicates. Cucumber variety was the main plot, while fungicide treatments were assigned to sub plots. Fungicides were applied once in 2 Weeks After Sowing (WAS) for 5 consecutive weeks. Data on disease incidence and severity were collected. Analysis of Variance was performed and significant means were separated using DMRT at a 5% significance level. Fungal pathogens were isolated on Potato Dextrose Agar (PDA), and residue analysis was done via UV-visible spectrophotometer. Result shows that FS, RG, and DF reduced LB incidence to 33%, 44%, and 77% respectively at 5 WAS compared to control 100%. However, all treatments showed 100% LB incidence at 7 WAS. The DF fungicide had the lowest disease severity (1.33), followed by RG (1.67) and FS (2.00), while control had the highest (3.67). Fruit rot incidence was lowest on FS (5.56%), followed by DF (7.33%) and RG (9.22%), relative to 74% in the control. Disease severity was lowest in RG (0.22), DF (0.22), and FS (0.33), compared to 2.44 in the control. The FS fungicide enhanced the highest marketable fruit (91% = 5690.67g), followed by DF (89% = 4858.00g), and RG (84% = 3888.33g), compared to 35% yield and 720.67g weight in the control. Fungal species identified as associated with leaf blight symptoms included Aspergillus niger, Fusarium spp., Alternaria cucumerina, and Cercospora spp., while pathogenicity test confirmed Aspergillus flavus, Fusarium spp., and Pythium spp. as the causal organism for fruit rot disease. Residue analysis showed that Metalaxyl (0.000068 mg/kg), Mancozeb (0.000049 mg/kg), Azoxystrobin (0.000049 mg/kg), Difenoconazole (0.000032 mg/kg), Pyraclostrobin (0.000053 mg/kg) and Dithomethorm (0.000038 mg/kg) contamination of fruits remained within acceptable Maximum Residue Limits (MRLs).In conclusion, the three fungicides Five Star, Dew Force and Ridomil Gold along with early planting effectively reduced disease incidence and severity with good yield and had a standard safe residue level in cucumber fruits.