Efficacy of Fungicides for In vitro Control of Date Palm Black Scorch Disease Agent (Thielaviopsis paradoxa)

Seven fungicides (Bayleton, Benlate, Tilt, Vitavax, Antracol, Copper-oxychloride and Soufrel) were evaluated for the in vitro chemical control of Thielaviopsis paradoxa (de Seynes) Von Hӧhn. isolated from symptomatic date palm fronds showing typical symptoms of black scorch disease. The pathogen growth was assessed by inoculating plates containing potato dextrose agar (PDA)-fungicide mix at 10, 50 and 100 ppm a.i. of the respective fungicides with plugs from 4-day-old fungus culture. All tested fungicides caused significant reductions in the mycelial growth of the pathogen with significant variations in their efficacies. The systemic fungicides were found to be superior to the non-systemic ones and their inhibitive effective, with the exception of Bayleton, was profoundly stable. The ED50 values indicated that Benlate, Tilt and Vitavax ranked on the top (ED50 = 4 and 5 ppm), Bayleton and Antracol were intermediate (ED50 = 14 and 20 ppm respectively) while Copper- oxychloride was the least efficacious fungicide in this respect (ED50 = 100 ppm). However, the antifungal activity of all tested fungicides appeared to be fungistatic since the treated fungus presumed growth in few to several days of incubation in clean PDA plates.