Abstract
As synthetic insecticides can have environmentally detrimental side effects, it is desirable to limit their use while still achieving good marketable yield. One approach is to apply pesticides only when needed, as determined by an action threshold (AT), defined as the number of pests per crop plant or damage intensity at which application is recommended. Another approach is to adopt alternative pesticides, such as botanical biopesticides, which can also be applied according to ATs. Here, ATs are developed in cabbage pest management using both approaches against the moths Plutella xylostella (L.), Helicoverpa armigera (Hubner) and Spodoptera litura (F.) and the aphid Brevicoryne brassicae (L.). Action thresholds were derived using fixed spraying regimes for the synthetic insecticides (imidacloprid and Voliam Flexi) and for azadirachtin, a neem-derived botanical. For synthetics, derived ATs are 40 individuals per plant for B. brassicae, 0.3 larvae for P. xylostella and 0.2 medium-sized larvae for H. atmigera and for S. litura. For H. armigera and S. litura, negative relationships between marketable yield and pest were found when larvae were medium or large sized, but not when larvae were small. Compared to synthetics, benefits of using neem formulations include higher action thresholds against P. xylostella (0.6/plant) and H. atmigera (0.4/plant) and an oviposition deterrent effect against S. litura. Overall, botanical insecticides were effective alternatives to synthetic pesticides. Although regional limits may apply to the accuracy of any ATs derived, the approach used towards their establishment is simple and transferable to other agricultural regions and crops.