Extracts of five plants, namely Argemone mexicana, Artemisia absinthium, Cassia occidentalis, Cymbopogon citratus and Siegesbeckia orientalis were tested for their antifeedant and insecticidal effects on third-instar larvae of the cabbage webworm, Crocidolomia binotalis, which is presently one of the most important pests of cruciferous crops in Mauritius. All the five plant species investigated showed significant antifeedant properties, with A. mexicana showing the highest control potential of the five plant species studied against C. binotalis.

An economic threshold on fresh cabbage affected by Plutella xylostella (L.) and Crocidolomia binotalis Z., based on visual estimates of defoliation and a determination of this damage on the marketable yield was developed. An initial survey of unprotected cabbage field for determination of general levels of number of holes caused by feeding of both the lepidopterous pests formed a prerequisite for conducting visual damage threshold experiments. Maintaining a low visual damage threshold of up to 1.0 mean hole (mean of two leaves) on the wrapper leaves, after initial protection of primordia, was found to be an effective alternative in reducing present reliance on weekly or fortnightly sprays for the control of both the pests on cabbage. The possibility of eliminating precupping sprays is supported by the study since the larval populations causing damage to either outer leaves or leaves about to cover the head did not reduce the yield to a significant extent. The use of thresholds based on larval counts of either P. xylostella or C. binotalis failed to give enough lead time during scouting and resulted in loss of marketability.

Various planting patterns of cabbage and tomato were investigated to assess whether such a cultural practice could fcring about reduction in the incidence of Plutella xylostella (L.) and Crocidolomia binotalis Z. on cabbage. No reduction in the larval incidence of both the pests was observed when different combinations of cabbage and tomato were planted at the same time. A slight reduction in the incidence of both the lepidopterans had ensued in all the planting patterns, when cabbage was planted 15 days later than tomato. Maximum reduction, however, was observed following planting pattern of one row cabbage and one row tomato (cabbage planted 30 days later than tomato). It is further opined that this type of cultural practice cannot be used as a sole control measure for both the pests, since the marketable yield of cabbage recorded in the promising intercrop combination was well below the attainable yield that could be expected when insecticide sprays are undertaken on pure cabbage. Significant reduction in net return was also obtained following this cultural practice as compared to cabbage receiving insecticidal sprays based on different management programmes.