RECENT PROGRESS IN INTEGRATED PEST MANAGEMENT OF VEGETABLES

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1 RECENT PROGRESS IN INTEGRATED PEST MANAGEMENT OF VEGETABLES Eizi Yano Division of Entomology, National Institute of Agro-Environmental Sciences, 3-1-1, Kannondai, Tsukuba, Ibaraki 305, Japan ABSTRACT Biological control is expected to become the basic system of IPM to control vegetable pests in Japan, as part of safe and labor-saving crop production both in greenhouses and in the field. Growers using greenhouses in Japan have their choice of eight species of commercially produced natural enemies. However, extreme temperature conditions in greenhouses, delay of release and the effect of chemicals are major limiting factors affecting the control capability of natural enemies in commercial greenhouses. Recent trials carried on IPM in the field are based on conservation of indigenous polyphagous predators, using selective pesticides. INTRODUCTION The basis of integrated pest management (IPM) for vegetables is the use of natural enemies. Seasonal inoculative release of natural enemies is the key technology in IPM to control greenhouse pests. In contrast, it is the conservation of indigenous natural enemies which is essential in IPM to control vegetable pests in the field. In Japan, protected cultivation in glass and plastic greenhouses has made rapid progress since the 1960s, and the total protected area is about 50,000 ha. Biological control of glasshouse pests using arthropod natural enemies has become important since the 1970s in Western Europe (Ravensberg 1992). Biological control is also expected to become the basic system of pest control in Japan for safe and labor-saving crop production in greenhouses (Yano 1993). Eight species of natural enemies were available for commercial use in greenhouses in Cultural control measures such as field hygiene or prevention of pest immigration are fundamental for the effective control of pests. Several kinds of plastic and other materials (nets, screens etc.) have been developed for the physical control of greenhouse pests, and are widely used in Japan (Yano 1996a). The application of selective pesticides and ecologically selective ways of using pesticides are also important in making pesticides compatible with the use of natural enemies in integrated control. Integrated use of natural enemies and other compatible control measures for each crop are essential for commercial application. Recently, some trials have been carried out to develop IPM for vegetables in the field. These are based on the conservation of indigenous polyphagous predators such as Orius spp. in eggplant fields and spiders in cabbage fields. Conservation is made possible through the use of selective chemicals. Vegetation management for conserving natural enemies has also been important in some studies. INTEGRATED PEST MANAGEMENT FOR PROTECTED CROPS The Greenhouse Environment in Japan Several differences are found between the greenhouse environment in Japan compared to Western Europe. In Japan, it is characterized by: Cultivation in small plastic greenhouses; High temperatures from spring to autumn and relatively low temperatures in winter; High humidity all year round; Immigration of pests from surrounding landscape because there is poor isolation from the outside environment. Keywords: Biological control, IPM, Japan, vegetable pests 1

2 These conditions cause several problems in pest and disease control, including a need for frequent applications of pesticides and fungicides, rapid population growth of pests, and unfavorable conditions for some of the natural enemies. Chemical control of pests is not easy, and is always accompanied by the risk of development of resistance to pesticides. Most greenhouse pests in Japan are cosmopolitan. They are all small in size, and suck fluids from plants. They belong to several groups of insects or mites, such as aphids, whitefly, thrips, mites and leafminers. In addition, there are sometimes outbreaks of noctuid moths in greenhouses in the southwestern part of Japan. Another important fact is that several exotic pests are causing serious damage to protected cultivation. Following the rapid development of greenhouse cultivation in the 1960s, Trialeurodes vaporariorum invaded Japan in 1974, and Thrips palmi around More recently, new strains of Bemisia tabaci (B. argentifolii), Liriomyza trifolii and Frankliniella occidentalis were reported as new pests around Another important factor is the high level of activity by indigenous natural enemies, which sometimes completely suppresses the pests in greenhouses. History of Biological Control for Protected Crops in Japan Phytoseiulus persimilis has a long history of study in Japan, where it was introduced in A voluntary research group was formed for fundamental and applied studies on its use as a predator (Mori and Shinkaji 1977). After this study, several production facilities for the predator were constructed and the predators produced were distributed in several prefectures. However, its use by farmers was not developed until recently, because of the limited supply, and the lack of integrated control systems for greenhouse crops. Although P. persimilis was registered as a biotic pesticide and commercialized in 1995 for controlling spider mites on strawberries, the area of use is limited. Encarsia formosa was imported from the UK in 1975, the year after the first recognition of the occurrence of Trialeurodes vaporariorum in Japan. The effects of temperature and release methods on the control capability of E. formosa were evaluated in greenhouse trials, and in a simulation model of the host-parasite population interaction (Yano 1989a,b, Yano 1987, 1990). The use of imported bumble bees, Bombus terrestris, for pollination is increasing among tomato growers in Japan. This is helpful for the production of good quality fruits, but the application of insecticides must be regulated after bumble bees are introduced into greenhouses. E. formosa is expected to give good control of whitefly provided care is taken in pesticide applications. After its registration as a biotic pesticide in 1995, the area in which the parasite is being released is increasing. The use of P. persimilis and E. formosa is not sufficient to develop a full system of IPM for a particular greenhouse crop. Aphids, as indigenous pests, are very difficult to control. Pests imported after 1980 have also become a major problem for many crops. There are two approaches to the biological control of pests. One is the use of imported natural enemies which are commercially produced in Europe and North America. Natural enemies imported by private companies are being tested in many agricultural experimental stations in Japan for possible registration as biotic pesticides for commercial use (Table 1). Trials are not always successful. This is partly due to the lack of sufficient experience of these exotic natural enemies on the part of the researchers involved. Another approach is the use of indigenous natural enemies. Although most serious pests are exotic species from abroad, indigenous natural enemies can be used to control them if they are released by seasonal inoculative release. This procedure is preferable to the use of imported species, from the point of view of the possible effect of imported species on indigenous species in agro-ecosystems. Promising results were obtained in the use of Orius sauteri for the biological control of Thrips palmi. It suppressed the increase of T. palmi on eggplant in greenhouse trials (Kawai 1995). Since O. sauteri is expected to be an effective biocontrol agent for T. palmi on greenhouse eggplant (Yano 1996b), rearing techniques in the laboratory are being developed using eggs of Ephestia kuehniella or acarid mites. Biological studies on development and predation are also being carried out, using T. palmi or aphids. A simulation model is being developed for evaluating the effectiveness of O. sauteri under different conditions. Factors Limiting the Use of Natural Enemies Technically, temperature extremes in greenhouses and the effect of chemicals are the two major factors affecting the control capability of P. persimilis in commercial greenhouses. Monitoring of early infestations by spider mites to determine the time of introduction of P. persimilis is also crucial for the 2

3 Table 1. Imported natural enemies to be registered for commercial use commercial use of this predatory mite, because spider mite outbreaks in Japan are more likely to occur in spring. Delay of release in greenhouse and low temperatures in winter are two major factors in the failure of E. formosa to control whitefly. Monitoring of the early infestation by whitefly is of paramount importance, because delay in the release of E. formosa is a major reason for its failure. Trapping of adult whitefly by yellow sticky traps, and checking the occurrence of adults on each plant based on binomial sampling, have been developed as effective monitoring methods. Most insecticides are harmful to E. formosa except for some insect growth regulators, while many acaricides and fungicides are less harmful. The most important technical factor in commercializing natural enemies is to integrate their use with other control measures. If the control measures for other pests are incompatible, the practical use of natural enemies is almost impossible. Social limiting factors in biological control are: Low tolerance of pest damage; Poor supply of natural enemies; Poor advisory services for farmers; Need for registration (Yano 1993). The low tolerance of pest damage among consumers is the main difficulty in use of biological control in flower production. Lack of a system for supplying enough natural enemies of good quality is another limiting factor in Japan. Most private companies in Japan have only recently become interested in biological control. However, many commercialized species of natural enemies are imported by private companies, and the production of indigenous natural enemies has now begun in Japan. If these natural enemies are commercialized after registration, sufficient numbers of natural enemies can be supplied. A good advisory service for farmers is very important to obtain good performance by natural enemies. At present, natural enemies used in protected culture must be registered as biotic pesticides. Present registration system based on that used for chemical insecticides is expected to be simplified in the near future. Cultural and Physical Control Although cultural and physical control measures do not have a curative effect after heavy infestations of greenhouse pests, their preventive effect on the rapid increase of pests is of great importance in integrated control. Their effectiveness is related to their impact on population build-up or dispersal. Thrips palmi is a species of subtropical or tropical origin, and unable to survive in the field in Japan over the winter (Ikeda 1983). The suppression of T. palmi in greenhouses before winter should decrease population densities in the following season. It is also difficult for the new strain of Bemisia tabaci (B. argentifolii) also to survive over the winter. Most greenhouse pests are polyphagous, and can eat many kinds of crops and weeds as host plants. If suitable host crops are cultivated, or host weeds grow near greenhouses, the pests can migrate from the greenhouse to surrounding fields and vice versa. Host weeds growing in greenhouses are also important for the survival of pests after harvesting. Removal of host weeds inside and near greenhouses and avoidance of cultivation of host crops are a fundamental part of preventive cultural control. Helgesen and Tauber (1974) pointed out three possible routes of introduction of Trialeurodes vaporariorum into greenhouses: 3

4 Artificial introduction of infested seedlings; Infestation from weeds or other crops in the greenhouse; Infestation from host plants outside but near the greenhouse. This suggests several possibilities for control by preventing the artificial introduction or dispersal of pests. These include the cultivation of clean seedlings in nurseries, removal of host weeds from greenhouses and the use of netting to cover the openings of greenhouses to prevent the immigration of pests from outside. These techniques are also applicable to other pests. Plastic films which absorb ultraviolet rays (UVA) are commonly used to cover plastic greenhouses in Japan. One important and interesting effect of this practice is to prevent the immigration of pests from outside. It is effective against aphids, whiteflies and thrips. Another important physical control measure is the use of colored traps. Winged aphids and whitefly adults are attracted to yellow, while adult thrips prefer white or blue. Many types of colored sticky traps have been developed, and are used for mass trapping or monitoring of these pests. Their main practical prupose is to monitor the effectiveness of chemical or biological control. Yellow sticky traps can also be used to determine the optimum time of release for Encarsia formosa, and to evaluate its effectiveness. Future Prospects for Integrated Pest Management Since the number of natural enemies available for biological control is limited, the integrated use of natural enemies and other control measures is essential for commercial application. Suitable crops for integrated control using natural enemies are those attacked by a small number of serious pests, those for which a low level of pest damage is tolerable, and those which require insect pollinators. Tomato and strawberry are both promising crops for integrated control in Japan. Fortunately, E. formosa can be used on tomato, and P. persimilis on strawberry. Table 2 shows a hypothetical integrated control scheme for tomato, combining natural enemies and selective pesticides. Two major problems are the control of the new strain of B. tabaci, and control of L. trifolii. E. formosa is not very effective against B. tabaci, but use of a parasitoid species, Eretmocerus eremicus, is promising. Indigenous parasites are expected to control L. trifolii on tomato. Sporadic increases in aphids can be controlled by the application of a selective pesticide, pirimicarb, or the application of a non-persistent chemical such as dichlorvos. Noctuid moths sometimes cause severe damage in south-western Japan, but can be controlled by Bacillus thuringiensis or insect growth regulators.. Soil application of systemic pesticides, and spot treatment with non-selective pesticides, are also possible options in integrated control. In Western Europe, integration of natural enemies and selective pesticides is emphasized (Ravensberg 1992). However, the greenhouse environment in Japan is less favorable for biological control, because of the temperature extremes and poor isolation of the greenhouse environment from its surroundings. Integration with other control techniques is needed for more satisfactory biological control. Cultural methods such as removal of host weeds are fundamental. Once pests become established in a greenhouse, their number increases almost exponentially in the high temperatures which occur from spring to autumn. In such cases, delaying the release of natural enemies often results in the failure of biological control. Monitoring to detect early infestation by pests in greenhouses is crucial for successful biological control. The use of resistant varieties of crops should also be explored. Partial resistance is adequate for integrated control (de Ponti et al. 1983). In conclusion, the integration of all possible pest control methods is needed for successful and use of natural enemies in Japan. INTEGRATED PEST MANAGEMENT IN THE FIELD Integrated Control of Thrips palmi in Eggplant Fields The effectiveness of Orius sauteri in suppressing T. palmi has been evaluated in several different ways in Okayama Prefecture. Eggplant grown in pots were introduced into a screen-house, and both T. palmi and O. sauteri were released. After the plants had been sprayed with fenthion, which controls O. sauteri but does not affect T. palmi populations, T. palmi increased rapidly. If no fenthion was applied, T. palmi was kept to a very low level (Nagai et al. 1988). Similar experiments were carried out in open fields of eggplant. When the eggplant were treated with fenthion, the peak density of T. palmi was four times as large as on the untreated plants (Nagai 1990a). 4

5 Table 2. A hypothetical system for integrated control of tomato pests Further experiments were also conducted using the selective pesticide pyriproxyfen, which has a control effect on the pupal stage of T. palmi but is harmless to O. sauteri. T. palmi on eggplant decreased rapidly after this pesticide was applied, due to the combined effect of the pesticide and O. sauteri (Nagai 1990b). The effectiveness of an IPM program which combined naturally occurring Orius spp. with selective pesticides was evaluated in eggplant fields in Fukuoka Prefecture (Takemoto and Ohno 1996). In most of the fields surveyed, the number of insecticide applications needed and the damage to the eggplant by T. palmi were both markedly reduced in comparison with fields given conventional treatment. In the fields with successful IPM, indigenous thrips species had been abundant when Orius spp. colonized the eggplant fields. With regard to the vegetation around the eggplant fields, O. sauteri was predominant on white clover and O. nagaii on paddy rice. It is likely that the surrounding vegetation serves as a reservoir for Orius populations on eggplant. Table 3 shows the list of selective pesticides applied in IPM fields. Indigenous natural enemies were conserved in the IPM system, and effectively suppressed other pests such as cotton aphids, spider mites, and broad mites. IPM of Cabbage Pests The key pest of cabbage in Japan is the diamondback moth (DBM). Resurgence and the development of resistance to insecticides is serious in this pest. IPM is based on the non-chemical control of DBM, combined with selective chemicals to control other pests. There are several options for the non-chemical control of DBM. Commercialized sex pheromone dispensers are promising but have some limitations. A net screen is an effective way of excluding DBM. Field hygiene is fundamental to prevent the migration of DBM into the field from surrounding areas (Tanaka 1993). If effective populations of natural enemies occur in the field, conserving them is an effective way of suppressing outbreaks of DBM. A system of selective pesticides has been proposed to conserve natural enemies (Nemoto, personal communication). REFERENCES De Ponti, O.M.B., M.M. Steenhuis, and P. Elzinga Partial resistance of tomato to the greenhouse whitefly (Trialeurodes vaporariorum Westw.) to promote its biological control. Mededlingen van de Faculteit Landbouwwetenschappen Rijksuniversiteit Gent. 48,2: Helgesen, R.G. and M.J. Tauber Biological control of greenhouse whitefly, Trialeurodes vaporariorum (Aleyrodidae: Homoptera), on short-term crops by ma- 5

6 Table 3. A list of selective chemicals applied in IPM fields of eggplants (Takemoto and Ohno 1996) nipulating biotic and abiotic factors. Canadian Entomologist 106: Ikeda, F Ecology and control of Thrips palmi Karny on the muskmelon in greenhouses in Shizuoka Prefecture. Shokubutsu Boeki (Plant Protection) 37: (In Japanese). Kawai, A Control of Thrips palmi Karny (Thysanoptera: Thripidae) by Orius spp. (Heteroptera: Anthocoridae) on greenhouse eggplant. Applied Entomology and Zoology 30: 1-7. Mori, H. and N. Shinkaji Biological control of tetranychid mites by Phytoseiulus persimilis Athias-Henriot in Japan. Japan Plant Protection Association, Tokyo (In Japanese). Nagai, K. 1990a. Suppressive effect of Orius sp. (Hemiptera; Anthocoridae) reared on Thrips palmi Karny (Thysanoptera: Thripidae). Japanese Journal of Applied Entomology and Zoology 34: (In Japanese). Nagai, K. 1990b. Effects of a juvenile hormone mimic material, 4 - phenoxyphenyl (RS) (2 - pyridyloxy) propyl ether, on Thrips palmi Karny (Thysanoptera: Thripidae) and its predator Orius sp. (Hemiptera: Anthocoridae). Applied Entomology and Zoology 25: Nagai, K., T. Hiramatsu and T. Henmi Predatory effect of Orius sp. (Hemiptera: Anthocoridae) on the density of Thrips palmi Karny (Thysanoptera: Thripidae) on eggplant. Japanese Journal of Applied Entomology and Zoology 32: (In Japanese). Ravensberg, W.J The use of beneficial organisms for pest control under practical conditions. Pflanzenshutz- Nachrichten Bayer 45/1992 1: (English edition). Tanaka, H The Diamonback Moth. Nobunkyo, Tokyo. (In Japanese). Takemoto, H. and K. Ohno Integrated pest management of Thrips palmi in eggplant fields, with conservation of natural enemies: Effects of surroundings and thrips community on the colonization of Orius spp. Proceedings, International Workshop on the Pest Management Strategies in Asian Monsoon Agroecosystems. N. Hokyo and G. Norton (Eds.). 320pp. Kyushu National Agricultural Experiment Station, pp Yano, E Control of the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) by the integrated use of yellow sticky traps and the parasite Encarsia formosa Gahan (Hymenoptera: Aphelinidae). Applied Entomology and Zoology 22: Yano, E. 1989a. A simulation study of population interaction between the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae), and the parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae). I. Description of the model. Researches on Population Ecology 31: Yano, E. 1989b. A simulation study of population interaction between the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae), and the parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae). II. Simulation analysis of population dynamics and strategy of biological control. Researches 6

7 on Population Ecology 31: Yano, E Use of Encarsia formosa (Hymenoptera, Aphelinidae) to control the greenhouse whitefly, Trialeurodes vaporariorum (Homoptera, Aleyrodidae), in Japan. In: The Use of Natural Enemies to Control Agricultural Pests, Food and Fertilizer Technology Center for the Asian and Pacific Region, Taipei, Taiwan, ROC, pp Yano, E Prospects for biological control in protected crops in Japan. Bulletin OILB/SROP 16,2: Yano, E. 1996a. Recent advances in biological and integrated control of glasshouse pests in Japan. In: Proceedings, International Workshop on the Pest Management Strategies in Asian Monsoon Agroecosystems, N. Hokyo and G. Norton (eds.). 320pp. Kyushu National Agricultural Experiment Station, pp Yano, E. 1996b. Biology of Orius sauteri (Poppius) and its potential as a biocontrol agent for Thrips palmi Karny. Bulletin OILB/SROP 19,1: DISCUSSION A participant from Taiwan noted that in Japan, natural enemies are registered as biopesticides. She pointed out that this is not required in Taiwan, and asked what kind of data are needed for registration in Japan. Dr. Yano replied that in Japan, if natural enemies are sold are sold to farmers as commercial products, the law requires that they should be registered. Those producing the product are asked to carry out experiments to demonstrate its effectiveness. Six trials in two years are common. However, what procedure should be followed in registering natural enemies and other biological products is still under discussion at the Ministry of Agriculture, Forestry and Fisheries. Participants at the seminar discussed greenhouse pests, and the immigration of insects into the greenhouse. One participant asked about emigration, and whether greenhouses may serve as a refuge in winter for insect pests which in summer move out onto crops. Dr. Yano agreed that a greenhouse may be a reserve for insect pests which cannot overwinter in Japan. This is why control from spring to autumn is important, to reduce the general density of such pests. In spring or autumn there is often an insect outbreak in the greenhouse, and insects emigrate. It was pointed out that Bemisia in central Asia survives the winter in greenhouses, from where it emerges in spring to attack cotton and other crops. Bemisia was not a serious pest problem in the area until greenhouses came into use a few years ago. 7