Cabbage Integrated Pest Management : An Ecological Guide.

Major Cabbage Insect PestsParasitic wasps usually are more effective at low pest population densities, whereas predators are moreeffective at high population densities. Parasitism can be quantified by counting the number of emptywhitefly pupal cases with a circular exit hole (created by the emerging adult wasp) rather than a “T”shaped split (created by the normal adult whitefly emergence).In Cebu, the Philippines, field parasitism of whitefly by the parasitoid Encarsia sp. ranged from 75 to90%! (Ref. FAO-ICP progress report April 1996 – Feb 1999).Numbers and activity of whitefly parasites and predators can be encouraged by avoiding broad-spectruminsecticides, planting of refuge crops, and -in some areas- augmentative releases.Whitefly mortality from pathogenic fungi often reach high levels in greenhouses where relative humidity isconstantly high and spores naturally accumulate. Pathogenic fungi can be applied as a spray treatmentand are effective at any population density. Insect pathogens used for whitefly control must be appliedwith good coverage and under proper environmental conditions (high relative humidity) to be effective. Thefungus Verticillium lecanii is commercially available in Europe for the control of greenhouse whitefly.Other products are being tested in commercial production fields and greenhouses, but the economicfeasibility of their use has yet to be determined.Another fungus called Paecilomyces fumosoroseus is also commercially available for whitefly control. Itcan be applied as a spore solution and it has some activity against aphids, thrips and spider mites. InCebu, Philippines, Paecilomyces sp. was found native in the field (Ref. FAO-ICP progress report April1996 – Feb 1999).Management and control practicesWhitefly management in a crop will depend greatly on the severity of damage caused in that crop and thenumber of whiteflies required to cause this damage. Very few whiteflies are required to transmit viruses,so where this is the major concern, a farmer will want to avoid even small numbers of whiteflies. Wherelow levels of whiteflies are tolerable, which is the case in most cabbage growing areas, other methodssuch as biological control can be more effective.Prevention activities:· Plant resistant cabbage varieties where available. Check local seed supplier in areas where whiteflyis a serious problem.· Proper monitoring of the whitefly population should be done regularly to detect early infestation. Theeasiest method of monitoring for whiteflies is leaf inspection. Sampling 100 leaves per field (one leafon each of 100 randomly selected plants) can provide a very good estimate of the average whiteflypopulation density in the field, but fewer samples are usually all that is needed to make a controldecision.· The movement of whitefly adults can be monitored with yellow sticky traps. This method can providea relative measure of general population trends over an extended area. In China for example, thesetraps are widely used in both greenhouses and in the open field. Careful monitoring of the types andnumbers of insects caught on the traps should be done as yellow traps may also attract largenumbers of useful natural enemies! When this happens, the traps are better removed from the field.· Destroy old crop residues that harbor whitefly infestations unless large numbers of natural enemiesof whitefly are detected.· Susceptible crops should not be grown continuously because whitefly populations expand rapidly ifthere is a continuous supply of food.105 Cabbage Ecological Guide - 2000