Using undersown clovers as living mulches: effects on yields, lepidopterous pest infestations, and spider densities in a Hawaiian broccoli agroecosystem

A field study was conducted to examine the influence of undersowing broccoli (Brassica oleracea var. botrytis L.) with living mulches (cover crops grown concurrently with a primary crop) on lepidopteran pest and spider densities and crop yield. In the present study, broccoli was grown in bare ground or undersown in strawberry clover (Trifolium fragiferum L.), white clover (Trifolium repens L.), or yellow sweetclover (Melilotus officinalis L.). Lepidopteran egg and larval densities were significantly greater in broccoli monoculture compared with broccoli – living mulch habitats during the latter part of the broccoli growth cycle. Although spiders were found more frequently on bare ground broccoli during early crop growth, during the ladder growth period, spiders counts were significantly higher on broccoli in living mulch habitats. Lepidopteran contaminants of harvested broccoli heads were significantly fewer in undersown than in monoculture broccoli. Broccoli heads were of similar size in living mulch and bare ground habitats. Yellow sweetclover gave the earliest and greater coverage among the living mulches, but broccoli heads were significantly smaller in these plots compared with white clover and strawberry clover plots. We discuss the reasons for variation in arthropod population responses to habitat types and the implications of the current findings on the future use of living mulches to depress insect pest populations.