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The perfect stage of Gibberella fujikuroi (Sawada) S.Ito., Bakanae disease fungusof rice plants, was often found on diseased rice stems in siverely infested fields inautumn. It was distributed widely throughout Miyagi prefecture.

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One hundred and twenty isolates of Pseudocercosporella herpotrichoides, causal fungus of eyespot of wheat, were tested for sensitivity to benzimidazoles (thiophanatemethy 1 and benomyl). They were divided into three types; sensitive, moderately resistant and highly resistant, of which minimum inhibitary concentration (MIC) to benomyl is 2mg, 20mg and > 200mg/l, respectively. Surveys of 2 78 winter wheat fields randomly selected in Hokkaido in 19 8 9, showed that benzimidazoleresistant strains were common and widespread. Resistant strains were obtained from 65.5% of fields and the proportion of resistant isolates was 5 0.0%. In the eastern region, where benzimidazole fungicides have been applied to control sclerotinia snow mold, most of all strains were resistant to benzimidazole. Experiments in three fields, where the frequency of resistant isolates was different, suggested that benzimidazole fungicides were able to control eyespot in such fields as frequency of resistant isolates were below 30%.

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Carrot bacterial gall, caused by Rhizobacter daucus Goto et Kuwata 1988, has been one of the majour soil-borne disease of carrot (Daucus carota L.) in Aomori prefecture. D if f erence in disease severity of several carrot cultivars were estimated under naturally infested field conditions and pot experiment with infested soil. C ultivar “Y oumei-gosun” showed significantly less disease severity than those as “H arumaki-kinkougosun” and the others.

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Garlic cv.“Fukuchi howaito” showing mosaic symptoms on leaves, were collected in Aomori prefecture. And the detection of garlic latent virus (GLV) from these plants were carried out by inoculation test and dot immunobinding assay (DIBA).All Fukuchi howaito tested were not infected with GLV. Several cultivars of garlic collected from southwestern parts of Japan were found to be infected with GLV. GLV in Rakkyo (Allium chinense) produced necrotic and chlorotic local lesions on Chenopodium amarnticolor, C. quinoa, Tetragonia expansa and broad bean.

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Some viruses isolated from some vegetables and legumes in Nanbu rigion of Aomori prefecture, were identified by means of inoculation of saps into test plants, electron microscopy in observation of infected leaves using the dip method and serological test. Tobacco mosaic virus was isolated from tomato cv.“momotaro” induced necrosis on fruits and leaves. Turnip mosaic virus was isolated from Chinese cabbage and Japanese radish. Cucumber mosaic virus was isolated from Japanese radish. Two strain of bean yellow mosaic virus were isolated from broad bean, pea, French bean and white clover. White clover mosaic virus was isolated from white clover.

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One virus, spherical particle with ca. 3Onm in diameter, isolated from Gentian showing mosaic on the leaves, was identified as an isolate of cucumber mosaic virus (CMV). A Gentian isolated of CMV reacted with CMV-O antiserum. The another type of viruses, spherical particle with ca. 25nm in diameter, was isolated from both Gentian showing necrotic spot on the leaves and Prairie Gentian showing chlorotic line pattern on the top leaves. The virus was identified as isolates of broad bean wilt virus (BBWV). They were divided into two isolates of BBWV by the experiments based on host range and antigenic properties against the antiserum of carrot isolate.

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Distribution of benomyl-resistant strains of Venturia nashicola Tanaka et Yamamoto was surveyed in 1979-1982 and 1989 at several orchards located in Miyagi prefecture. The detection rate of isolates resistant to benomyl was more than 85% in 1979 through 1989. Although the detection rate of highly resistant isolates are reduced, weakly resistant and intermediately resistant isolates are not reduced by discontinued spray applications of thiophanate-methyl and/or benomyl.

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Size-controlling rootstocks have generally been selfrooted by grafting their scions on rootstocks cuttings of Malus prunifolia BORKHAUSEN var.ringo ASAMI in Japan. In Aomori Prefecture, the rootstocks have widely been used without removing a rooted portion of M. prunifolia ringo.Thus a rootstock is composed of two rooted portions;M. prunifolia and the size-controlling rootstock.If either a size-controlling rootstock or a cultiver scion carriesapple chlorotic leaf spot virus (ACLSV), the virus will cause innerbark necrosis andpittig on M. prunifolia ringo.
Effect of the ACLSV on the occurrence of white root rot caused by Rosellinia necatrix BERL.or violet root rot caused by Helicobasidium mompa TANAKA was evaluated in the field.Seedlings of M.scheidekeri Z.which is susceptible to the ACLSV were used as the rootstock.After planting apple trees in an orchard infested with high density of pathogenic fungi, half of them were inoculated with the ACLSV and others were left free from the virus.The trees inoculated with the ACLSV were more susceptible to the two fungi than ACLSV-free trees.According to the survey at an orchard where the violet root rot was predominant, trees showing necrosis symptoms induced by ACLSV on the part of M. prunifolia ringo were more affected by H. mompa than those without the symptoms.

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Feeding inhibitory responses of adult rice water weevil, Lissorhoptrus oryzophilus Kuschel to methanol extracts of non-host plants were examined by the application of the extracts on rice leaf surface.Only the extracts of Solidago gigantea and S. altissima inhibited feeding among 20 plants (dicotyledon) examined. S. gigantea and altissima would contain feeding deterrents of rice water weevil.Non acceptance of the other non-host plants may result from the absence of feeding stimulants and/or physical factors, e.g.leaf shape and hardness.

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Individuals of the green rice leafhopper, Nephotettix cincticeps, used in this study were collected from four regions in Miyagi Prefecture. Population less susceptible to malathion and fenobucarb occurred at first in some regions. Median lehtal dose of malathion in population from Rokugo, Sendai was 68.4 μg/g. As malathion had been used broadly in Miyagi Prefecture, this less susceptibility may be related to the extent of control using malathion. However, in spite of few number of applications, susceptibility to fenobucarb decreased in populations from two regions which were especially less susceptible to malathion.

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Developmental periods of the small brown planthopper, Laodelphax striatellus Fall'en were examined at five temperature conditions. Developmental velocity was linearly related to the temperature from 15 to 25°C. Within the range of these temperatures, developmental zeros of egg, female nymph and male nymph were 10.5°C, 11.2°C and 11.0°C, respectively. At high temperatures of 30°C or 32.5°C, developmental velocities were not accelerated linearly with increasing temperature and their variations were larger than at low temperatures.

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In Morioka City which is in the inland area of Iwate Prefecture, the population density of A.solani on the soybean fields became maximum in June. On the other hand, in Taneichi Town which is in the Pacific coast area, population growth of A.solani was delayed and the density of aphids became maximum in July.The density of aphids in Taneichi Town reached to higher level than in Morioka City: the peak value of the mean density of A. solani on six varieties of soybeans in Taneichi Town became 2.6 fold of one in Morioka City.
The mean temperature of a day in Taneichi Town was 3.1-3.7°C lower than in Morioka City from June to July in 1989 and these lower temparature is a suitable condition for the survival and reproduction of A.solani. So it was assumed that differences on the population growth and the peak level of the density of A.solani between in Morioka City and in Taneichi Town were partly caused by the difference on the daily temperature between the two places.
Th reproduction of A.solani was ceased by the insecticide (ethylthiomethone) application either in Morioka City or in Taneichi Town.The incidence of the soybean dwarf disease was also decreased by the insecticide application in Taneichi Town.The same application, however, was not effective in Morioka City. Without the insecticide application, the percentages of the soybean dwarf incidence in Taneichi Town were higher than in Morioka City.It was supposed that high percentages of the soybean dwarf incidence in Taneichi Town were due to the frequent transmission of the soybean dwarf virus caused by the high density population of A.solani in the soybean fields.

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The peak densities of A. solani populations were varied among six varieties of soybeans (Okusirome, Ohousyu, Suzukari, Tsurukogane, Wasesuzunari, Raiden) in 1989.In Morioka City, the maximum value of the peak density was observed on Tsurukogane and the minimum value was on Suzukari.In Taneichi Town, on the other hand, the maximum value was observed on Wasesuzunari and the minimum value was on Okusirome.The incidences of the soybean dwarf disease were also varied among the varieties of soybeans.In Morioka City, the maximum value of the incidence of the disease was observed on Suzukari and the minimum value was on Ohousyu.In Taneichi, on the other hand, the maximum value was observed on Suzukari or on Wasesuzunari and the minimum value was on Tsurukogane. Ohousyu and Tsurukogane are known as the resistant varieties to the soybean dwarf disease and the incidences of the disease on these varieties were always lower than on the other varieties.Although the values of the peak density of aphids and the incidence of the soybean dwarf disease were varied among the varieties of soybeans, there was no significant relationships between the aphid density and the incidence of the soybean dwarf disease.

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