The Efficacy of Companion Planting Rosemarius and Allium with Brassica spp to Control Cabbage Looper Damage


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By Julie Forkner

Advised by Dr. Mark Beaudreau
presented 07 Oct 1996

As the threat of environmental and human poisoning by agricultural pesticides looms, alternatives to chemical controls are increasingly needed. Companion planting offers a non-poisonous, safe way to reduce damage done by insects and other pests, as well as reducing the cost of other resources. According to the repellent crop set forth by the Rodale Institute, the smell of Rosemarinus (rosemary) and/or Allium (onions) will repel Pieris rapae and Trichopulsia ni when planted as companions with Brassica oleracea (cabbage), thus reducing damage by those insects to the cabbage. In this experiment, white cabbage cv. Early Jersey Wakefield was intercropped with white onions and prostrate rosemary. Two separate, consecutive experiments were run within the same growing season. Insect populations were measured periodically. Leaf area damage and biomass were assessed at the end of the growing period. Data on Trichoplusia ni was unobtainable due to low populations. An analysis of variance showed that in the first run, there was no significant difference in the amount of damage done to monocropped cabbage as compared to those grown with companions. However, the second run, more successful in terms of seedling survival and plant maturity, showed that cabbages grown with onions suffered significantly less damage than those grown alone or with rosemary, thus supporting the hypothesis that onions are repellent to cabbage moth caterpillars. Evidence suggests that osemary may be attracting Pieris rapae. More research on this observation is needed.