Use of tropical basil to reduce Hellula undalis F. incidence on cabbage in south Benin

Vegetable plays an important role in most food safety programs around the world. In West Africa, they significantly contribute to the quality of the diet of the population and to the incomes of many families. Among these vegetables, cabbage (Brassica oleracea L.) is one of the most cultivated. However, its production is severely limited by the pest pressure. H. undalis is an important pest of this crop because each attack induces the total loss of the plant: the larva of this insect destroys the heart of the cabbage inducing the formation of cabbages with multi-head without commercial value. Field trials were conducted during the dry and rainy season at Abomey-Calavi in the south Benin to evaluate the potential of tropical basil (Ocimum gratissimum L.) for managing cabbage webworm H. undalis. Two intercropping modalities were evaluated and compared to the control (cabbage alone): (1) cabbage plants in alternated rows with tropical basil plants, and (2) cabbage plot framed by tropical basil plants. The number of H. undalis larvae was counted once a week for eight weeks. The proportions of marketable and the multi-head cabbages were evaluated at harvest. Four replicates were performed for each treatment.
The results have shown that there were relatively more numbers of H. undalis larvae on the cabbage alone, whereas lower numbers of larvae were counted when cabbage was planted with tropical basil. Generally, damages were also more on cabbage alone than cabbage intercropping with tropical basil. The marketable cabbage was relatively higher in the intercropping plots compared to cabbage alone. Among, both the intercropping design alternated row system showed the best results in terms of educing pest populations and damage than the cabbage plots framed by tropical basil.
In conclusion, intercropping tropical basil/cabbage plants reduces H. undalis infestations on cabbage and improves production. These results indicate that this traditional vegetable (tropical basil) could be used in integrated pest management programs for other vegetables also. Optimizing of this agro-ecological approach could minimize the use of synthetic pesticides and consequently improve food and environmental sanitary quality.