[in Japanese]

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Recently, the occurrence of the so-called pseudo-sheath blight, similar to the lesions of rice sheath blight caused by Rhizoctonia solani (AG- 1, sasakii type), is causing problems at harvesting time of rice plant. The lesions are mainly caused by the following three fungi, culture type III B of Rhizoctonia solani (brwon sheath blight), Sclerotium oryzae-sativae (brown sclerotium disease) and Rhizoctonia oryzae (bordered sheath spot) . The symptoms induced by artificial inoculation of these fungi were compared with the symptoms of sheath blight. Type III B of R. solani and S. oryzae-sativae were mainly isolated from pseudo-sheath blight lesions of rice plants collected from paddy fields at harvesting time

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The moisture level required for the control of potato common scab caused by Streptomyces scabies (illegal name) was analysed in composing several moisture regimes. Limit of irrigation point to control scab seemed to correspond to pF 2. 2-2. 3, and these values were suitable for maximum potato production. A significantly lower scab incidence resulted from irrigation was recorded in soils with a low pH value (pH 5. 2-5. 4) unlike in those with a higher pH value (pH 6. 0-6. 5). Therefore irrigation and fungicide treatment (PCNB and Trichlamide) were tested to evaluate their effect on scab in fields with a high pH value, where no scab reduction by irrigation had been achieved. An additive effect between irrigation and chemical treatment was eventually observed.

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[in Japanese]

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Occurrence of leaf yellow and wilt disease of eggplant from spring to autumn in the field in 1982 and in semi-forcing culture in vinyl houses in 1984 was observed in Saga prefecture. One kind of the fungus, Verticillium sp. which was isolated with a high frequency from vessel tissues of the infected plants caused wilting of eggplant seedlings by artificial inoculation. The optimum temperature for mycelial growth of the fungus on PDA medium was 20-25C and limited mycelial growth was observed even at 30C. Based on the results of a morphological comparison of the isolates with standard fungus and pathogenicity against test plants, the fungus isolated from eggplant was identified as Verticillium dahliae KLEBAHN.

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[in Japanese]

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[in Japanese]

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Four methods of detection of Rhizoctonia spp. in the soil of Japanese radish fields were compared to analyse the ecological behavior of the fungus. In the soil of the fields, a higher frequency of Rhizoctonia spp. was observed with the bait methods using stem of flax or straw of barley than with the plant debris method and the contact slide method. Besides, as a trapping plant, the stem of flax was superior to the straw of barley. By artificial inoculation of soil in pot experiments, the detection ability of these methods ranked as follows: the bait method using stem of flax> the bait method using straw of barley> the contact slide method> the plant debris method. It was considered that the bait method with flax was more effective even in the soil with a low density of the fungus. The contact slide method did not enable to isolate the fungus. Thus, it is suggested that the bait method with flax may be a suitable method to detect and isolate Rhizoctonia spp. in the soil of Japanese radish fields.

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Field surveys of soil-borne diseases revealed that the first outbreak of root rot of Chinese cabbage had occurred in Kikuchi and Kamoto Districts in Kumamoto Prefecture in 1984, though the disease had not been reported hitherto in Kyushu. The disease was prevalent at the rate of about 19 to 80 per cent in seven out of twelve cabbage fields surveyed which consisted of diluvium humic soil (loam). Serious outbreaks of the disease were exclusively observed in fields under reated cultivation of cruciferous crops, and in those where the crops had been planted earlier during the end of July to the middle of August ahead of the usual schedule for autumn-winter cultivation. Affected cabbages showed symptoms from the beginning of September to the middle of October. Some of the plants died or were severely affected due to root constriction, one of the typical symptoms. Aphanomyces sp. was observed in diseased cabbages, and was isolated from the seedlings with damping off in three kinds of cruciferous crops which were planted on the soil samples collected from the fields affected with the disease. The pathogen was identified as Aphanomyces raphani KENDRICK on the basis of its morphological characters and host range. The pathogen was detected in 10 fields out of 19 where cruciferous crops were cultivated in the districts.

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Onions grown in the recently reclaimed area of Ariake polder land in Saga prefecture were found to be less resistant to black mold caused by Aspergillus niger VAN TIEGHEM than those grown in areas cultivated for a longer period of time. The contents of Mg++ and Na+ and K+ in the soil of the recently reclaimed areas were about two times higher than those in the soil of the areas cultivated for a long period of time. In a water culture experiment, Ca++ absorption by onion grown in liquid medium with high contents of Mg++ and Na+ decreased when compared to that of onion grown in a solution with low contents of Mg++ and Na+. On the other hand, the onions cultured in a medium with high contents of Mg++ and Na+ showed an incresed susceptibility to the disease. Based on the results of experiments on the inhibition of the antagonistic absorption by Mg++ and Na+, negative correlations between Ca++ content in onion bulbs and the susceptibility of onion to the disease were detected.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Two Japonica type breeding lines of rice, Saikai 165 and Saikai 168 bred from a highly resistant variety, Mudgo, were tested to evaluate the mechanism of resistance to the brown planthopper, Nilaparvata lugens STAL. The nymphs caged on the breeding lines at the early tillering stage did not exhibit a high mortality nor a low rate of adult emergence, but showed a slightly slower rate of growth than those on a susceptible variety, Asominori. The longevity of the adult females was similar between the breeding lines and the susceptible variety, but egg production on the breeding lines was reduced to 1/2-1/4 at the tillering stage of rice. The breeding lines were less preferred by the macropterous females both in the laboratory and in the field tests. In the field tests conducted in 1981 and 1983, the population density of the brown planthopper re-mained significantly low until harvest time in the breeding lines, while the density increased in the succeeding generation and hopperburn occurred in the susceptible variety. It is suggested that the mechanism of resistance resulting in the suppression of the planthopper population was mainly associated with non-preference and to some extent with antibiosis.

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[in Japanese]

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The rice leaf roller moths of the 3rd generation occurring in fall showed signifi-cantly greater sizes than those occurring in the other seasons. Field collections of the final instar larvae in the paddy fields among the different growing stages and laboratory rearing experiments under various daylength and temperature conditions were performed to analyse the environmental factors controlling the body size of the moths. Young host plants, low temperature and long daylength increased the body size of the insects. Temperature had the most pronounced effect on the body size changes. The relative growth ratio of the body, "wing loading index (pupal weight/square of forewing length)", increased with pupal weight, while these increase rates seemed to be different between populations growing in different temperatures, i. e., moths reared at 26 *C had relatively smaller wings than those reared at 21°C for the same pupal weight. The main cause of the appearance of bigger moths in fall is considered to be the low temperature prevailing during the growing period of the generation.

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Invasion of the rice water weevil (Lissorhoptrus oryzophilus KUSCHEL) in Fukuoka Prefecture was first confirmed in June 1983. The occurrence was limited to only five paddy fields on the small island of "Oshima" and 9 adult weevils were collected in 15a paddy fields in the first survey. In the following year, however, the weevil spread to the whole area of the island, and the adults were observed in paddy fields as far as 1.6 km apart from the sites where they first occurred. In the same year the weevil occurred in Shingu town and Iizuka city. Shortly after transplanting was performed on May 8, overwintered adults invaded the paddy fields and started to infect rice seedlings. Adult density increased rapidly to reach a peak at the end of May, but it decreased rapidly in early June. Two-year survey on Oshima island showed that the weevil maintained a high reproductive rate in the years immediately after the initial invasion.

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Diazinon, isoxathion and cartap were sprayed on rice plants. The amount of the insecticides recovered from rice plants were measured by GLC at intervals. Furthermore, experiments to investigate the cause of pesticide disappearance from rice plants were also performed. Initial deposition ratios of diazinon, isoxathion and cartap on rice plants were 5.90, 18.4 and 7.79% respectively. In the case of organophosphates, the disappearance curve of pesticides on rice plants consisted of two periods apparently. In the initial period (0-1day), the amounts of diazinon and isoxathion decreased very rapidly, the half lives of these insecticides being 0.35 and 0.92 day, but in the later period (3-15 days), the disappearance of the insecticides was very slow, the half lives being 4.8 and 5.0 days, respectively. Photodecomposition and volatilization tests were carried out using test tubes (Pyrex glass tube covered with aluminum foil, Pyrex glass tube, and quartz tube) and Petri dishes. Diazinon, isoxathion and cartap were slightly decomposed by sunlight.. Diazinon was very volatile, and only 0.1% remained in Petri dishes 8 hours after application, but 92.0% of cartap remained in the Petri dishes 8 hours after application. In conclusion, volatilizaton was the most important factor, for the disappearance of diazinon and isoxathion on rice plants, while the role of photodecomposition was negligible.

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The appearance of pesticide residues in paddy, irrigation, and creek water was monitored in Saga Agricultural Experiment Station, in 1981 for chlormethoxynil, CNP (chlornitrofen), oxadiazon and pyrazolate, and in 1983 for CNP, simetryn, oxadiazon and diazinon. When the precipitation was low, 20% of diazinon, 3% of simetryn and 0.05% of benthiocarb, CNP, and chlormethoxynil applied on paddy fields were estimated to reach the water. When the precipitation exceeded 70mm, 3% of oxadiazon and pyrazolate applied on paddy fields was recovered in the water.

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Eggs and adults of phytopahgous stink bugs were subjected to a census at intervals of 1 week in a soybean field in Fukuoka during the period from late June to mid October in 1984. Eggs and adults of four stink bugs, Riptortus clavatus, Piezodorus hybneri, Eysarcoris guttiger and Megacopta punctissimum were detected in the census field. Egg parasitism of these stink bugs involved four parasitoid species: Ooencyrtus nezarae collected from all the four host species, Telenomus sp. from P. hybneri and E. guttiger, Ooencyrtus sp. from R. clavatus and P. hybneri, and Gryon hakonensis from R. clavatus. Although parasitism of host eggs by G. hakonensis and Ooencyrtus sp. was found only during the period from late July to early August, parasitism by O. nezarae and Telenomus sp. was continuously observed throughout the census period. This seasonal pattern of parasitism by the latter two species may be ascribed to the reproduction in the census field associated with their short generation times and the continuous host supply for a long period.

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The occurrence of the soybean pod gall midge, Asphondylia sp. and its ectoparasitoid, Philomacroploea pleuralis was studied in Kagoshima Prefecture in 1951-52 and in Kanto district in 1956-57. These studies showed that there were 2 peaks of occurrence in the middle of June and the middle of September in Kagoshima, and 1 peak around the middle of September in the Kanto district. The parasitoid was considered to be one of the effective agents of control of the gall midge population, because of its relatively high percentage of parasitism in both the area. However, no detailed information is available on the biology of the parasitoid. The changes in the age structure observed in the present study revealed that P. pleuralis had at least 2 generations from June to November, and the parasitic activity of the wasp declined from August to September. The relationship between the density of the parasitoid and that of the soybean pod gall midge was not clear. The pattern of seasonal changes in the percentage parasitism observed in the period 1980-82 was similar to that in 1951-52, but the percentages were not as high as those recorded about 30 years ago. In recent years many paddy fields have been converted into soybean fields. The soybean pod gall midge has been noted to occur in such newly established soybean fields soon after the beginning of cultivation. It is remarkable that P. pleuralis was found in the present study to attack the host midge immediately after the invasion of the gall midge to the drained soybean fields. This finding suggests that P. pleuralis had been present somewhere near the soybean fields attacking hosts other than the soybean pod gall midge.

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[in Japanese]

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Developmental process in the larval stages of three major sweet potato defoliators, Aedia leucomelas LINNE, Agrius convolvuli LINNE and Brachmia triannulella (HERRICH-SCHAFFER), was examined to obtain basic information for the analysis of population changes in the field. Larvae of A. leucomelas were reared under different conditions of temperature and day length on mature or immature sweet potato leaves. Most of the larvae were in the 5th or 6th instar, but the total developmental period was almost identical at 25°C. The number of moltings was more affected by the quality of food than by the temperature and day length. The mean growth rate of the head capsule width of the 5th and 6th instar forms was 1.901 and 1.547, respectively. In A. convolvuli, all larvae fed the sweet potato leves developed to the 5th instar at 25°C in the laboratory. The mean growth rate of the head capsule width was 1.701, which corresponds to DYAR's formula. It was confirmed that larvae of B. triannulella were in the 4th or 5th instar. When they were reared on sweet potato leaves in June, 5th instar forms appeared at the rate of about 40 percent. The mean growth rate of the head capsule width of the 4th and 5th instar forms was 1.628 and 1.429, respectivery.

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Interspecific competition between T. palmi and A. gossypii was examined in potted and open field eggplant. In potted eggplant, the population of T. palmi become extinct regardless of the initial densities of these two species. When A. gossypii invaded and reproduced in open field eggplant, the population of T. palmi decreased rapidly. A. gossypii always defeats T. palmi and T. palmi is eliminated in the interspecific competition between these two species on eggplant.

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[in Japanese]

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[in Japanese]

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The diamondback moth, Plutella xylostella L., is known to be resistant to various kinds of insecticides. In Japan some strains of the moth are resistant to organophosphorus and carbamate insecticides, but no obvious resistance was previously observed for pyrethroid insecticides. This paper is intended to report a new evidence of the declined susceptibility of the diamondback moth to pyrethroid insecticides. A first failure in controlling the moth population with a mixture of fenvalerate and malathion was noted at a cabbage field in Mizobe, Kagoshima Prefecture in summer of 1984. In that field, a mixture of 0.01% fenvalerate and 0.03% malathion has been sprayed since summer of 1983 at a rate of 200 to 300l per 10 a. LC₅₀ values were determined in the laboratory by the leaf or body dipping method. The laboratory experiments indicated that the diamondback moth extremely reduced its susceptibility to the pyrethroids tested. The moth was also reconfirmed to be less susceptible to organophosphate and carbamate insecticides, but it was still susceptible to Bacillus thuringiensis preparations.

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Soil samples taken from a sweet potato field on August 20, after a period of drought lasting approximately one month when weeds were wilting in the daytime, and on Aug. 28, 8 days after the beginning of rain, were divided into two parts, ie. fine soil and aggregated soil (more than 5 mm in diameter), by sifting with a 5 mm aperture sieve. Root fragments caught on the sieve were also collected to obtain egg-masses. Nematodes were extracted from the two soils by the double-layer centrifugal-flotation method and a combination of this method and Baermann funnel method. Nearly twice as many eggs and ten times more hatched larvae per egg-mass as well as a significantly higher proportion of second-larval-stage eggs were observed within the egg-masses collected on Aug. 20 as compared to those collected on Aug. 28. Approximately 3, 000 living larvae per 100 ml of soil, most of which were physiologically young in terms of their food reserves, were extracted on Aug. 20, while the number of larvae on Aug. 28 (after the rain) showed a drastic increase (about 6, 000). Both the increasing rate of larvae caused by the rain and the proportion of living larvae in the fine soil were higher than in the aggregated soil. These results indicate that hatching of eggs and emergence of larvae from egg-masses are remarkably suppressed by drought which ordinarily occurs in summer in Kyushu, and larvae in soil can well withstand such conditions. Drought is considered to affect the pattern of seasonal population changes of this nematode.

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Investigations were carried out on the nemastatic effects of nematicides (MK-166 and oxamyl) on embryonic development, larval emergence from egg masses, and egg-laying activity of female adults of the root-knot nematode, Meloidogyne incognita. The embryonic development of eggs laid in equilibrated saline solution was more retarded by MK-166 (88-350 ppm) than by oxamyl for the same dosage of the product. Seasonal variations of the susceptibility should be taken into account for the evaluation of the chemicals. The larval emergence from egg masses was more inhibited by MK-166 (88-350ppm) than by oxamyl. The egg masses should be, exposed to the chemicals for at least 2 weeks. Both chemicals most affected the development of nematodes 6 to 10 days after the penetration to host plants at 18.4°C, bringing about the highest depression of egg-laying activity of the females.

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