Simple SummaryCabbage maggot is a devastating pest of cole crops such as broccoli, cauliflower, Brussels sprout, cabbage, and turnip in the Central Coast of California. Organic and conventional growers in the region have limited access to non-chemical management options. To develop a trap crop, understanding the relative susceptibility of brassicas to cabbage maggot is essential. Thus, brassicas were evaluated as companion plants with broccoli and lettuce after exposure to cabbage maggot flies. In 2013 and 2014, cabbage maggot flies were observed to lay more eggs at the base of turnip plants than broccoli. The larval feeding damage was greater on turnip than on broccoli. Lettuce (a non-brassicaceous crop) was included in the experiment to determine if it could suppress cabbage maggot attacks on broccoli. Lettuce did not reduce cabbage maggot infestation on broccoli after planting side-by-side. Additionally, the number of eggs and larval feeding damage were lower in cauliflower than in broccoli. Cabbage maggot infestation on cabbage was not different from that on broccoli. This study suggests that turnip should be further evaluated by planting on border rows of fields, or as an intercrop, to manage cabbage maggot in broccoli in the Central Coast of California.AbstractCabbage maggot,Delia radicum(L.) (Diptera: Anthomyiidae) is a serious pest ofBrassicasuch as broccoli (Brassica oleraceavar.italicaPlenck) and cauliflower (B. oleraceaL. var.botrytis) in California’s Central Coast. Since there are limited non-chemical options available for growers to manageD. radicum, there is an urgent need to develop alternative tactics. The objective of this study was to determine the effects of side-by-side plantings of turnip (Brassica rapavar.rapaL.), lettuce (Lactuca sativaL.), cauliflower, and cabbage (B. oleraceaL. var.capitata) with broccoli onD. radicuminfestation. In 2013 and 2014, the experiments were conducted in Salinas, California. Significantly greater numbers of eggs and larval feeding damage were found on turnip compared with broccoli. Lettuce (Asteraceae), a non-Brassicacrop, was compared with broccoli; however, lettuce did not reduce oviposition or larval feeding damage on broccoli. The larval feeding damage on cauliflower was significantly lower than on broccoli when planted side-by-side. The effects on cabbage were not significantly different from broccoli in terms of oviposition and larval feeding damage. This new information generated from the Central Coast of California will be further utilized to develop a trap crop to effectively tackle theD. radicumproblem inBrassicafields.