Field trial of eight varieties of brassica field crops in the Auckland district I. susceptibility to aphids and Virus Diseases

Under field conditions Broad-leaf Essex rape and Superlative swede were highly susceptible to cabbage aphid (Brevicoryne brassicae), Wye swede and chou moellier (marrow-stem kale) were moderately susceptible, Doon Spartan and Calder swedes were resistant and York Globe and Green Globe turnips were highly resistant. Varieties did not show the same order of resistance towards Myzus persicae as towards B. brassicae. Calder and Doon Spartan swedes and chou moellier were highly resistant to turnip mosaic, while these varieties together with Wye swede were moderately resistant to cauliflower mosaic. The turnip varieties had a high incidence of both virus diseases. Virus disease was the primary cause of plant mortality. The time of virus infection was correlated with aphid flights. It is suggested that part of the difference in virus incidence was due to vector behaviour. Chou moellier and Doon Spartan swede were outstanding for winter survival and yield. Calder and Wye swedes were next best, but none of the other varieties was satisfactory under the conditions of this trial.