Cabbage Integrated Pest Management : An Ecological Guide.

Major Cabbage Insect PestsLarval development takes some 30 to 35 days. There usually are five instars.Pupation takes place in a silken cocoon, usually in the leaf litter or crop debris. In cabbages, the cocoonmay also be in the heart of the plant between leaves. The pupa is brown and about 20 mm long. Underoptimum conditions, development of the adult inside the cocoon takes about 15 days.In (sub)tropical areas there may be 5 generations per year or more as a result of continuous breeding.Even in temperate areas, the caterpillars continue to be active at low temperatures.Plant damageThe caterpillars of the semilooper eat large, irregular holes in the leaves. Young larvae skeletonize leaves,the older larvae eat the entire leaves, sometimes causing plant defoliation. As loopers mature, they movedeeper into the cabbage heads. They can consume large parts of the hearts of cabbages, and contaminatingit with frass. Plant development may be retarded and the quality of cabbages will go down.Compared to other caterpillars, cabbage loopers are not very destructive. Although one looper larvaedoes approximately three times the damage of one Pieris rapae larva and can consume almost 20 timesas much foliage as a diamondback moth larvae, their numbers are less and they do not eat deep in theheart of the cabbage.There are pheromones available for looper monitoring.Natural enemiesMany natural enemies are recorded for this species and natural field mortality may sometimes be high.Nuclear Polyhedrosis Virus (NPV) and Bacillus thuringiensis (Bt) are effective against this pest. However,some trials report that Bt is less effective against the cabbage looper.During the wet season, some fungus species may attack and kill the cabbage looper.Management and control practicesPrevention activities:· Removing or burning of crop residues and removal of weeds help to lower the pest population.Cabbage loopers may survive on crop stubble and weeds after harvest and infest a newly transplantedcrop, causing new crop injury.· Ploughing the field may bury crop residues containing looper pupae in the soil where they die.Once cabbage loopers are present in the field:· Hand collection of larvae may be possible for small plots. It may not be practical for cabbageproduction on larger scale.· Biological control with preparations of Bacillus thuringiensis (Bt) may be effective. Bt is mostlikely to be effective on young, active looper larvae exposed during time of application.· Chemical control has been difficult to achieve as the cabbage looper has developed resistance tomany insecticides including carbaryl, parathion, methomyl and others.99 Cabbage Ecological Guide - 2000