60 Pest management for Head Cabbage Production on Guam R. Muniappan and Mari Marutani Agricultural Experiment Station, College of Agriculture and Life Sciences, University of Guam, Mangilao, GU 96923 USA Abstract Cruciferous crops on Guam are infested by cabbage webworm, Hellula undalis (F.), cabbage cluster caterpillar, Crocidolomia pavonana Zeller, mustard aphid, Lipaphis erysimi (Davis), armyworm, Spodoptera litura (F.), flea hopper, Halticus tibialis (Reuter), fire ant, Solenopsis geminata (F.), leaf miners, Liriomyza spp., diamondback moth, Plutella xylostella (L.), corn earworm, Helicoverpa armigera (Hübner), and garden looper, Chrysodeixis chalcites (Esper.). Because cabbage (Brassica oleracea var. capitata L.) is one of the economically important vegetables on Guam, we have been developing an integrated pest management program for this crop. Hellula undalis is a serious problem on seedlings in nurseries as well as transplanted young plants in the field. Naled was effective in contolling this pest on young seedlings. Radish (Raphanus sativus L.) and green mustard (B. juncea L.) can be utilized as trap crops in the field for this pest. Similarly, the incidence of C. pavonana on cabbage was curtailed by growing Chinese cabbage (B. pekinensis (Lour.) Rupr. cv. Tempest), or flowering green mustard next to cabbage. The population of H. tibialis on cabbage was also considerably reduced when it was grown with radish, Chinese cabbage or mustard as trap crops. Liriomyza spp. population was very low as the introduced parasites effectively suppressed them. Spodoptera litura was attracted to cabbage more than other crucifers. Pydrin (fenvalerate) is effective in controlling this pest. Solenopsis geminata occasionally became a problem in newly transplanted fields during the dry season. Drenching with diazinon controlled this ant. Diamondback moth was a serious problem in one of the trials conducted in 1988. Seasonal variation in occurrence of this pest was evident and it was noted only in the dry season. Information on diamondback moth in terms of host preference and effective insecticides remains to be determined. Introduction Crucifers constitute one of the common groups of vegetables grown in Guam and other Micronesian islands. Main cruciferous crops include cabbage (Brassica oleracea var. capitata L.), Chinese cabbage (B. pekinensis (Lour.) Rupr.), pak choi (B. chinensis L.), and radish (Raphanus sativus L.). On Guam, a total of 10 arthropod pests have been recognized in association with cruciferous crops: the cabbage webworm, Hellula undalis (F.) (Lepidoptera: Pyralidae), cabbage cluster caterpillar, Crocidolomia puvonana (F.) (Lepidoptera:Pyralidae), mustard aphid, Lipaphis erysimi (Davis) (Homoptera:Aphididae), corn earworm, Helicoverpa armigera (Hübner) (Lepidoptera:Noctuidae), armyworm, Spodoptera litura (F.) (Lepidoptera:Noctuidae), diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera:Yponomeutidae), garden looper, Chrysodeixis chalcites (Esper.) (Lepidoptera:Noctuidae), flea hopper, Halticus tibialis (Reuter) (Hemiptera: Miridae), fire ant, Solenopsis geminata (F.) (Hymenoptera:Formicidae), and leaf 54 1 542 Muniappan and Marutani miners, Liriomyza spp. (Diptera: Agromyzidae) (Stevens and Muniappan 1977). Hellula undalis, C. pavonana and DBM are mostly host-specific to cruciferous crops while the rest have a wider host range. Hellula undalis is native to the Old World. At present, it has spread to parts of Australia and to the Pacific islands. Distribution of this insect primarily depends on flying ability of the moth (Shirai and Kawamoto 1990). In Taiwan, Chinese cabbage is more heavily infested by H. undalis than common cabbage, and the infestation is only seen during the months of June- October (Talekar and Lee 1985). Application of Bacillus thuringiensis Berliner has been found not to be effective to control this pest in Singapore (Chang and Pegn 1971) and in Hawaii (Tanada 1956). Crocidolomia pavonana is a native of Africa and Asia, and is now distributed in tropical regions of Africa, Asia, Australia, and Pacific islands (Waterhouse and Norris 1987). Several studies on chemical control of C.pavonana have been documented. Fullerton (1979), for example, reported excellent control of this pest with fenvalerate and cypermethrin in the Cook Islands. In Papua New Guinea, Thistleton (1979) recommended acephate, tetrachlorvinphos and permethrin, and in Malaysia, B. thuringiensis was recommended by Ooi (1980). DBM, a cosmopolitan species of Mediterranean origin, has been studied extensively in many countries. Talekar et al. (1985) compiled information on various aspects of DBM including biology, ecology, sex pheromone, cultural control, biological control, chemical control, insecticide resistance, and integrated control. Recently, trap cropping with mustard was found to reduce the infestation on cabbage in India (Srinivasan and Krishna Moorthy 1988). In recent years, cultivation of some crucifers on Guam has decreased due to pest problems. Farmers either indiscriminately use available pesticides to overcome the problem or grow crops other than crucifers. Frequent applications of organophosphorus, carbamate or synthetic pyrethroid insecticides have led to the development of insect resistance to chemicals and have also resulted in failure of establishment of parasites or disappearance of the established parasites of DBM such as Cotesia plutellae (Kurdj.) (Hymenoptera:Braconidae), Thyraeella collaris (Grav .) (Hymenoptera:Ichneumonidae) , Tetrastichus sokolowskii Kurdj . (Hymenoptera : Eulophidae), and Diadegma insulare (Cresson) (Hymenoptera:Ichneumonidae) (Muniappan, R., unpublished data). Although Cotesia variventris (Hymenoptera:Braconidae) and Meteorus sp. (Hymenoptera: Braconidae), two larval parasites of H. armigera and S. litura, and Telenomus sp., an egg parasite of S. litura, were commonly found during 1976-78, they were rare in 1988-90. Obviously, either biological control or application of pesticides alone cannot be adopted as a sole control measure to overcome such a complex pest problem. We, therefore, explored alternative control measures and developed an integrated pest control program for the production of crucifers, especially cabbage on Guam. Occurrence of Pests on Guam More than 30 field experiments and surveys of farmers’ fields during 1988-90 confirmed occurrence of some pests on cruciferous crops reported by Stevens and Muniappan in 1977. Hellula undalis attacked young seedlings of crucifers in the nursery before transplanting and young plants in fields. It caused damage on terminal shoots and midribs of leaves. In severe cases, such damage to apical meristems resulted in the development of multiple heads of cabbage which were small and unmarketable. Spodoptera litura was another common pest that often attacked cabbage. There was a spatial variation in occurrence of this pest. Similarly, DBM was abundant at certain areas of the island, and also there was a seasonal difference in the incidence of this pest. It was found mostly during the dry season. During 1988-89, C. pavonana was found only occasionally, however in 1990, C. pavonana was one of the major pests on crucifers in the fields. Helicoverpa armigera, C. chalcites, H. tibialis, S. geminata, L. erysimi and Liriomyza spp. were of minor importance during this study. Pest Management on Guam 543 Host Preference Five trials were conducted at four different locations on Guam to find out host preference of pests on crucifers. All trials were arranged in a randomized complete block design with 3-4 replications and each plot consisted of four rows with a distance of 1 m between rows. The distance between adjacent plants within a row was 0.46 m or less depending on the type of plants. There were eight or more plants in a row and the population of each pest was recorded by counting the number of individuals on sampled plants in the inner rows of the plot. Cabbage and Chinese cabbage were germinated in trays and 3-4-week-old seedlings were transplanted in the fields. All other crops were sown directly in the fields. Prior to planting, all fields were thoroughly prepared by disc plowing and tilling. Then a complete fertilizer of 10-20-20 (N-P2O5-K2O)at 1102 kg/ha was applied and incorporated in the furrows. The fields were irrigated using drip systems. Hand-weeding and application of insecticides and fungicides were done when needed. All data were transformed to square root (X+0.5) before performing analysis of variance and means separation was done by Duncan’s multiple range test (SAS Institute 1985). The first trial was initiated on 12 October 1988 at Dededo in the central-northern part of the island. Tested plants included cabbage cv. KK Cross, Chinese cabbage cv. Tropicana, broccoli (B. oleracea var. italica), pak choi, rape (B. napus cv. Dwarf Essex) and radish cv. Relish Cross. There were three replications. DBM was the major pest in this trial. DBM started to appear on 3 November and the population increased so rapidly during the trial that on 25 November there was an average of 31.6 larvae and pupae/10 plants. Although there was no significant difference (P = 0.05) in the number of DBM among the crops tested, radish had the lowest number (17.3/10 plants) and cabbage had the highest number of insects (40.0/10 plants) on 25 November. Other pests found during the trial were C. chalcites, H. undalis, S. litura, H. tibialis, Aulacophora foveicollis (Lucas) (Coleoptera:Chrysomelidae) (a pest of cucurbits) and Liriomyza spp. Because of a low