Comparative Efficacy of Systemic and Combination Fungicides for the Control of Alternaria Leaf Spot of Cabbage
2023
Patience U. Ishieze | Chinedu F. Amuji | Kevin I. Ugwuoke | Paul K. Baiyeri | Michael O. Eze
Alternaria leaf spot of cabbage, caused by the <i>Alternaria brassicicola</i>, affects leaves of cabbages and often results in head rots causing severe decline in yield. In this work, the effects of systemic and combination fungicides on <i>A. brassicicola</i> mycelia growth in vitro and disease severity in field trials were investigated. The results of in vitro evaluation revealed that both fungicides significantly inhibited (<i>p</i> < 0.05) the growth of <i>A. brassicicola</i> under in vitro conditions. However, metalaxyl-M 6% was less effective with 100 μg/mL having only 30 ± 3.5% inhibition. On the other hand, 100 μg/mL of mancozeb 63% + carbendazim 12% had 94 ± 3.5% growth inhibition of <i>A. brassicicola,</i> respectively, under the same conditions. Dose-response analysis of the efficacy of the two fungicides showed that the LC<sub>50</sub> of metalaxyl-M 6% and mancozeb 63% + carbendazim 12% were 125.52 ppm and 57.22 ppm, respectively, indicating the superiority of combination fungicide over systemic fungicide alone. Field studies showed that while manure type significantly impacted on biomass production (<i>p</i> < 0.001), it did not significantly affect disease severity. On the other hand, the frequency of fungicide application impacted on disease severity, with biweekly application leading to a significant reduction in disease severity after 10 weeks.
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