Cabbage Integrated Pest Management : An Ecological Guide.

Major Cabbage Insect PestsSome NPV study data from VietnamA vegetable FFS-graduate farmer group in Ha Tay village, near Hanoi, started experiments with theuse of NPV against Helicoverpa and Spodoptera on cabbage and tomato. The group did both pottingexperiments and field studies with NPV which was supplied by the National Institute of Plant Protection.Some of the conclusions that were drawn from their potting experiments :· Larvae that die from NPV change color from green to yellow, they diesslowly (several days), the skin breaks easily, then fluid comes out,and the caterpillar may hang down from the leaves.· Small larvae are more susceptible than larger sized larvae. Mortalityrates were 100% for small, 90% for medium and 85,5% for large sizedlarvae. The group concluded NPV should be applied to the field whenlarvae are still small.· NPV did not have any effect on natural enemies in jar experiments.· Larvae infected with NPV die within 3 to 4 days.· NPV-infected larvae eat less (area of leaf) than healthy larvae.· In jars, NPV was still viable after 2 days but this may not be the casein field where there is sunshine, rain, etc.In a field study, the farmer group found that NPV gave 80% control of armyworm.The farmers concluded that NPV is better than chemical pesticides because it gives equal or bettercontrol of the specific pests. In addition, it may spread through populations in the field. However, theyalso recognized that the effect of NPV is short (break-down by sunlight) so it needs to be appliedmore often. On-farm production of NPV has not been tried so far by this group (pers. comm. Ha Tayfarmer group, April 2000).In Indonesia, the Biological Control Research Center (of the National Institute of Plant Protection, Indonesia)has developed a method of production and application of NPV, which can be done by farmers. Usually,starter cultures of NPV are supplied by institutes such as the National Institute of Plant Protection. Seesection 6.3.3 for NPV production guidelines and some quality matter.Other natural enemies:Preparations of Bacillus thuringiensis (Bt) have been found to be effective against armyworms.In Lao PDR, the larval parasitoid Microplitis sp. was found parasitizing Spodoptera in cabbage andcauliflower (pers. comm. A.Westendorp, 2000).Management and control practicesPrevention activities:· Burning of crop stubble and removal of weeds help to lower the pest population. The armyworms maysurvive on crop stubble and weeds after harvest and infest a newly transplanted crop, causing cropinjury.· Flooding of the infested field to drown pupae and other soil-inhabiting pests may be an option whenirrigation facilities exist. This should be done before preparing the land for a new crop.· Ploughing the field will bring larvae and pupae to the soil surface for exposure to sunlight or predatorslike birds.93 Cabbage Ecological Guide - 2000