Susceptibility of five cabbage varieties to attack by aphids (Hemiptera: Aphididae) in the Accra plains of Ghana

Abstract

We investigated the susceptibility of five cab bage varieties (‘Oxylus’, ‘Super Cross’, ‘Vantar F1 Hy brid’, ‘Santa’F1 and ‘Fortune’) to aphids. Trials were set up in the Accra plains for two rainy seasons in 2017. The first trial examined aphid infestation and the second included weekly blanket spray of neem oil at 0.48 L/ha (60 ml/15 L water) during the second rainy season. Five systematically sampled cabbage leaves per plot were examined for the numbers of aphids and associated nat ural enemies (predators). Symptoms of aphid attack (in cidence and severity of infestation) were also recorded. Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) were the two aphid species observed and their numbers differed signif icantly between varieties in both seasons during the first but not the second trial. Few aphids settled on ‘Oxylus’, while more occurred on ‘Fortune’. L. e. pseudobrassicae was the most abundant aphid on all the varieties. Aphid numbers were significantly decreased by neem applica tion. Occurrence of natural enemies did not differ signif icantly between varieties, except for spiders during the major rainy season. There was no significant difference in aphid infestation between varieties during the first season as all of them completely succumbed to the infestation, while in the second season aphid incidence and severity of infestation was highest on ‘Fortune’, with ‘Oxylus’ being the least attacked by aphids. The crop yield was zero during the first season without protection for all the varieties. However, in the second season, lower yields (0.19–3.66 t/ha) was obtained with cabbage without pro tection, and much higher yields (14.8–21.1 t/ha) were obtained on neem-treated plots.