Diamondback moth (Plutella xylostella) (DBM) is a major pest of forage brassica crops in New Zealand This study evaluated the effects of DBM larval feeding on three forage brassica crops in a greenhouse experiment DBM eggs in batches of 5 10 or 50 were placed on 6weekold potted kale rape and turnip plants Plant growth and development (main stem diameter plant height total number of stems and leaves and dry matter weight of roots and foliage (including stems)) were measured at harvest Additionally the number of pupae recovered was recorded None of the measurements of plant growth was influenced (P>005) by DBM egg density Percentage pupal recovery was consistent between treatments Larger DBM population sizes may have been required to show an effect on plant growth Implications of these results for DBM pest management are discussed