The effects of nitrogen and sulphur nutrition on the response of Brussels sprout plants to infestation by the aphid Brevicoryne brassicae

SUMMARY The effects of two levels each of nitrogen and sulphur nutrition and of infestation by Brevicoryne brassicae on the growth of Brussels sprout plants were studied in factorial experiments. All the plants receiving high nitrogen treatments grew more rapidly than those with low, but in infested plants the improvement in growth at the higher levels of nitrogen was offset by the increased size of aphid populations. Low sulphur nutrition increased the growth of plants receiving high nitrogen and of the aphids feeding on them. Leaf diffusive resistances and chlorophyll concentrations were greater with high nitrogen, but were significantly lowered by infestation in all nutrient treatments. Infestation decreased leaf total nitrogen concentration at the sites of feeding, but effects on soluble nitrogen were not significant. Removal of aphids 72 days after initial infestation did not cause marked plant recovery during the next 22 days. It is concluded that the benefits of increased yield resulting from high nitrogen levels must be balanced against the greater potential for damage by aphids.