An evaluation of some systemic fungicides for the control of Septoria leaf spot of tomato

Abstract

Three systemic fungicides viz. Thiophanate Methyl (Topsin M 70WP), Benomyl (Benlate 50WP) and Carbendazim (Bavistin 50WP) and a protectant, Mancozeb (Dithane M-45), were tested at Akomadan in Ghana for their efficacies and cost effectiveness against Septoria lycopersici Speg., which causes Septoria leaf spot of tomato. The optimal spray schedule for themost cost effective and most readily-available fungicide was also studied. In the dry season, when leaf spot was generally absent, no differences in efficacies of the fungicides could be detected. In the wet season, Septoria leaf spot severity was high and the three systemic fungicides were generally superior to the protectant, Dithane M-45. Among the systemics, Benlate and Topsin M performed similarly and were generally more efficacious than Bavistin. The cost effectiveness of the systemic fungicides in the wet season (indicated by benefit:cost indices (BCI) was highest for Topsin M (0.22-0.32 per cent) followed by Bavistin (0.11-0.23 per cent) and lowest for Benlate (0.07-0.13 per cent). Use of Topsin M (413 g a.i. /ha) at 1, 2 and 3-weekly applications, commencing 5 weeks after transplanting and terminating in the 9th week, resulted in area under disease progress curve (AUDPC) values of 26.83, 29.16 and 31.82 per cent wk, respectively. These values were all significantly lower (P=0.05) than the value of 38.73 per cent wk associated with the no fungicide treatment. Judicious pesticide use and possible measures for increasing tomato yields in the area are discussed.


(Ghana Journal of Agricultural Science, 1997, 30(1): 71-78)