All of the chemicals evaluated in field experiments, chloropicrin, D-D (1, 3-dichloropropene), MITC (methyl isothiocyanate), a mixture of D-D and MITC, metam-ammonium, DCIP (2, 2-dichlorodiisopropyl ether), and a mixture of chloropicrin and DCIP were effective for control of potato bacterial wilt caused by Pseudomonas solanacearum. Especially, injection of chloropicrin at 300l/ha, D-D at 400l/ha and a mixture of chloropicrin and DCIP at 300l/ha were highly effective. In these treated plots, the numbers of P. solanacearum in soil also decreased. A direct sterilizing effect of gas from these chemicals was recognized at 0.5mg/l of chloropicrin, at 5mg/l of MITC and at 10mg/l of D-D and DCIP in a 48 hour exposure test to the cultured pathogen. Results of the exposure test indicate that these chemicals have a direct effect in decreasing the density of the pathogen in soil and wilt incidence in the field.

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Rhizoctonia root rot of corn is a recently occurring disease which has been reported since 1980. To clarify the background of the disease's occurrence, 20 native varieties, 66 foreign varieties and 27 inbred lines were tested for resistance to the pathogen, Rhizoctonia solani AG 2-2. The commercial Fi variety P3358 was used as a standard. All of the 113 varieties or lines were found to be susceptible as well as the standard used. These results showed that corn was originally susceptible to R. solani AG2-2, and the disease's occurrence is not related with the corn variety. On the other hand, the pathogenicity of R. solani AG2-2 isolated from diseased plants of sugar beet and corn was compared through cross inoculation tests. The pathogenicity of corn strains was strong both to corn and sugar beet. The sugar-beet strains were more pathogenic to sugar beet, but clearly weaker to corn.

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Biological control and integrated control were tested for cabbage yellows caused by Fusarium oxysporum f. sp. conglutinans in a heavily infested field.
A single treatment of the suspensions of 3 mixed antagonists of Streptomyces sppor charcoal compost fixed with the antagonists, Bacillus subtilis and two isolates of Actinomycets slightly suppressed the disease incidence in the heavily infested field.
In order to protect plant from infested soil, a physical method of seedlings in small bags or long bags of woven polyester cloth ("root-proof" sheet) permeable to water and nutrients and placed into the planting holes was used. It suppressed the disease incidence drastically, especially when treated with biological control.
Cropping a resistant variety in the previous cultivation also suppressed the disease incidence in the next susceptible variety cultivated.
The population density of the pathogen in these cases was lowest inside of the "root-proof" bags, so the disease incidence did not appear to cause severe damage. While, antagonists treatments decreased the population density of the pathogen, the suppression of disease incidence did not appear to be so remarkable.
At the final check of disease incidence, I checked if plant roots were restricted inside the "root-proof" bags or not. In most cases, secondary roots grew out of the bags. However, they did not appear severely damaged.
These phenomena suggest the severity of disease was determined by the period of pathogen infection.

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Strawberry anthracnose has spread to major strawberry production areas with the change of varieties. The perfect stage of the pathogen was found in some areas of Japan, but was never found in Kyushu Island. We examined whether our isolates could form the perfect stage on nine agar media with or without illumination. Fifteen out of twenty-four isolates originating from the northern area of Kyushu formed perithecia and ascospores on oat meal agar (OMA). Formation of the perfect stage was superior on OMA than other media. The morphology and size of the perfect stage was similar to that of Glomerella cingulata. Benomyl resistance of the pathogen was also tested. Twelve isolates having 2, 000-4, 000 ppm MIC values were considered resistant strains and others having 2.5-20 ppm MIC values were considered susceptible strains.

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An isolate of tomato spotted wilt virus which was obtained from Cucumis sativus in vinyl house culture in Ishigaki Island, Okinawa seemed to be the same as TSWV-W. The percentage of infection of TSWV estimated by ELISA in the field was 64%. Cucumbers infected with TSWV showed star- or mesh-like chlorosis, chlorosis at the leaf edge and chlorotic spots. Masking of symptoms was observed after flowering stage of the host plant.

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[in Japanese]

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The satsuma dwarf virus recurs after 2-3 years when planted in an attacked orchard. Further, when the attacked tree is allowed to stand, this disease is propagated to the adjacent tree fundamentally affecting the management of citrus fruit in an attacked orchard. The authors conducted soil disinfection using soil burning, chemical disinfection with chloropicrin, deep tillage of infected soil and thorough disposal of infected roots in combination with deep tillage as post-measures in an orchard attacked by the satsuma dwarf virus in 1984. Thereafter, citrus virus free seedlings were planted and an ELISA test was performed. After 5 years there was recurrence in all of the post-measure groups at a low ratio. The test orchard was on a hillside and judging from the virus reaction observed in sakaki plants growing naturally in Doba, it is considered that the measures for complete soil disinfection are difficult in land of this sort.

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[in Japanese]

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The seasonal occurrence of loquat canker caused by Pseudomonas syringae pv. eriobotryae in spring buds and seasonal leaves in a field was surveyed for twenty years from 1970 to 1989. Severe occurrences of the disease were in 1981, 1985 and 1987 whereas the slight ones were in 1975 and 1977. The severity of disease development in spring leaves paralleled that in spring buds and the disease development in buds and leaves was affected by the precipitation and number of rainy days for about one month before and after the disease occurrence. The mean temperature in February and cold injury due to the occurrence of low temperatures during the sprouting season were the main factors for the development of canker lesions on spring buds. The disease infection did not decrease until 7 days after injury under high humidity conditions whereas the infection did not occur one day after injury under dry conditions. Branches and leaves of loquat were susceptible to the disease until five or six days after injury under high humidity conditions. The precipitation for five days after injury was closely related to the disease development, so that, much precipitation stimulated the occurrence of the disease. The density of phage of P. svringae pv. eriobotryae in rainwater was highest in the season from November to May and lowest from June to October based on three years of observations. There was a close relationship between the spread of canker lesions and the number of oriental fruit moth (Grapholita molesta Busck) living in lesions. From the result that the pathogenic bacterium was isolated from the body of the oriental fruit moth, it was suggested that the insect is able to propagate the canker disease.

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[in Japanese]

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Field surveys were couducted on the damage of sweet potato by sweetpotato weevil, Cylas formicarius (FABRICIUS) in sweet potato fields. Damage to sweet potato by larvae spread from vines to tubers, and also spread from the periphery of the field to the center. On the whole, the extent of damage by larvae to sweet potato vines and tubers was usually higher at the periphery of the field. The spatial distribution of damaged tubers in the field was analyzed by using the IWAO method (1968), and the result indicated a random distribution. Positive correlation was found between the number of punctures per tuber by feeding of adults and the degree of damage per tuber by larvae.

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Laboratory surveys were conducted to clarify the seasonal emergence of overwinting larvae and oviposition habit of sweetpotato vine borer, Omphisa anastomosalis GUENEE in Amami Oshima island in 1989-1991. Overwinting larvae collected in the field emerged from the begining of April to the middle of May. Most of the adults emerged by midnight from p. m. 8:00. to p. m. 12:00. Mating behavior were observed soon after emergence. Females began to oviposit within 1.5±0.5 days and longevity of females were 3.6±1.3 days. Females laid 130.0±79.3 eggs in life and most of the eggs were singly oviposited on the leaf and petiole of sweetpotato. Ovipositing, mating and flying were observed at night.

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[in Japanese]

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The survival of Meloidogyne incognita second stage juveniles (J2) and free living nematodes (F1) in soil infested with the nematophagous fungi Arthrobotrvs dactvloides (constricting rings) and Dactylella haptotvla (sticky knobs) was evaluated under various conditions. The system for testing survival consisted of 109 of an Andosol soil in 4.5cm diam petri dishes infested with a standard inoculum of 0.05g wet weight fungi/10 g soil. Nematodes were added in a 0. 5ml suspension of water. J2 survival was 8% of control when D. haptotvla was added to soil 2 days prior to adding nematodes but it was 85% in A. dactvloides infested soil under the same conditions. J2 numbers declined rapidly in D. haptotvla infested soil with 10% survival after 24 hours whereas J2 survival in A. dactvloides soil was 50% after 6 days. F1 nematode survival was affected in a similar way by both fungi. Steam sterilization did not appear to affect the trapping of J2 or F1 by either fungi under these experimental conditions.

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The effects of marketted forage crops on the population of root-knot nematode, Aleloidogvne incognita were tested using 2m×3m microplots. Guineagrass, cultivar Natsukaze (Panicum maximum) together with sun hemp cultivar Nemakorori (Crotalaria juncea, a green manure crop) suppressed the root-knot nematode population as low as fallow. Rohdesgrass cultivar Katambora (Chloris gayana) followed them, but sorghum cultivar Green Sorugo (Sorgum bicolor bicolor) and sudan grass cultivar Sudakkusu (S. bicolor drummondii) had inadequate or no suppressive effects. Growing guineagrass cultivar Natsukaze was regarded as a hopeful method to control root-knot nematode greenhouses vacant in summer.

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Characteristics of acetylcholinesterase (AChE) of Meloidogvne incognita and its inhibition by several insecticides were studied. When C-acetylcholine was used as a subsrate, AChE activity of lvi. incognita could be measured by using less than 10, 000 second stage larvae. Optimum pH for AChE activity was pH 7. 2-7. 7.
The AChE of M. incognita was strongly inhibited by carbofuran and diazoxon. Fenitrothion, diazinon, and parathion were less inhibitory to the AChE.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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The overwintering of the Hawaiian beet webworm, Hymenia recurvalis, pupae was examined in Nobeoka, Miyazaki Prefecture. The larvae were reared on Amaranthus lividus in Petri dishes during the autumn and the mature larvae were transfered for pupation to plastic containers containing a small amount of soil. These containers were kept outdoors in the shade and the emerged moths were recorded. The critical period during which the mature larvae were capable of emergeing was mid October in 1988 and late October in 1989, respectively. Thereafter no emerged moths were found. The depth of the cocoons in soil was also observed. The cocoons were found just below the soil surface to a depth of 3 cm and the depth didn't differ as the season progressed. These results suggest that the annual occurence of the pest in Nobeoka is caused by the migration of moths flying from overseas.

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Percent parasitism by Lysiphlebus japonicus ASHMEAD attacking the citrus brown aphid Toxoplera citricidus KIRKALDY were determined for host colonies of different sizes in field cages. The percent parasitism by the parasitoid was independent on the size of host colony. The number of adult parasitoids which attacked a colony were not different between colony sizes during two days after release of parasitoids. This lack of numerical response of the parasitoid seemed to be an important factor for the size-independent parasitization rate per colony.

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In a field application test, hanging polyurethane foam sheets (30×500mm) containing C. brongniartii (conidia 1.4×10 ⁸/cm ²), at the branching parts of fig trees (var. Houraishi) resulted in 62% mortality of yellowspotted longicorn adult beetles, P. hilaris, at the dosage of 2 sheets per tree. Pathogenicity of conidia on the polyurethane foam sheet applied to fig trees persisted for 45 days after application.

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[in Japanese]

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[in Japanese]

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The parasitization rate of the chestnut gall wasp, Dryocosmus kuriphilus YASUMATSU by the imported parasitoid, Torymus (Syntomaspis) sinensis KAMIJO has remained low and therefore the parasitoid has not yet effectively controlled the host cynipid. In order to determine the reasons, the detrimental effect of native facultative hyperparasitoids was investigated in an experimental orchard during 1989 to 90. As a result, it is suggested that parasitoid suffers a high mortality during the mature larval stage mainly due to the parasitization by several facultative hyperparasitoids such as an undetermined Eupelmus sp. and Eupelmus urozonus DALMAN.

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