根こぶ病は絶対寄生性の原生生物Plasmodiophora brassicaeによって引き起こされるアブラナ科作物の難防除土壌病害の一つである。我々は，キャベツ（Brassica oleracea L. var. capitata）の根こぶ病抵抗性品種および罹病性品種の連作が，根こぶ病の発病と土壌中の病原菌密度に与える影響を圃場レベルで調べた。抵抗性品種‘BCR龍月’および罹病性品種‘おきな’をそれぞれ4期繰り返し栽培したところ，罹病性品種連作区と比較して抵抗性品種連作区では土壌菌密度の有意な減少がみられた。一方，同期間を休閑とした無栽培対照区においても抵抗性品種連作区とほぼ同等の減少がみられ，両区間で有意差は認められなかった。上記の試験を行った後の試験区画にて罹病性品種‘おきな’を栽培したところ，無栽培対照区と比較して抵抗性品種連作区では発病が抑制される傾向にあった。また，‘BCR龍月’を栽培したところ，発病はほとんどみられなかったが，大型のこぶを持つ罹病性個体が1個体生じた。そこで，その原因菌（Shimo-22DM）を分離し，同抵抗性品種への再接種を行ったところ，明確な病徴はみられず，非親和性の菌群である可能性が示唆された。結論として，圃場での抵抗性品種の連作により，自然減の寄与があるものの，罹病性品種の栽培と収穫が可能なレベルまで土壌菌密度を低減できることが示された。
Considering the growing global demand for matcha, the Shizuoka prefectural government is promoting the export of matcha prepared from cover-cultured tea. To improve matcha production, it is important to investigate the characteristics of pest incidence under covering culture and develop suitable pest management strategies. In this study, we investigated the effects of direct tea plant covering and copper fungicide application to curb the incidence of tea anthracnose (Discula theae-sinensis (I. Miyake) Moriwaki & Toy. Sato), the most serious tea disease that occurs primarily during or after the second tea season. Our results indicated that the incidence of tea anthracnose decreased when cover culture treatment was used compared to that with no-cover treatment during the second tea season. In addition, the tea plants grown under cover and pre-treated with a copper fungicide showed less anthracnose symptoms during the sprouting period than those not treated with the fungicide. These findings suggest that tea anthracnose can be effectively controlled using covering culture after the application of copper fungicide.
This study investigated the sensitivity of 92 isolates of Passalora fulva from tomato plants in Wakayama Prefecture to thiophanate-methyl, penthiopyrad, boscalid, azoxystrobin, and triflumizole using agar dilution methods. All isolates exhibited reduced sensitivity to more than two fungicides. Bioassays using tomato seedlings showed that mancozeb WP (wettable powder), TPN WP, and iminoctadin-albesilate WP were effective against two strains resistant to multiple fungicides.
In recent years, Mie Prefecture has been working to establish a domestic production area for sesame (Sesamum indicum L.), and the cultivation area has been increasing. Meanwhile, there is a wide incidence of sesame bacterial leaf spot (caused by Pseudomonas syringae pv. sesami Young, Dye & Wilkie, Acidovorax valerianellae Gardan, Stead, Dauga & Gillis, and Xanthomonas sp.), contributing to yield loss. No pesticides against the disease are currently registered in Japan, and no control measures have been established. We evaluated three copper fungicides (basic copper sulfate, sodium bicarbonate/anhydrous copper sulfate, and basic copper chloride/sulfur) in pot and field tests. Our results demonstrated that all fungicides could suppress the disease when applied before its onset or in its early stage.
We investigated the effects of alternating applications of Bacillus spp. and Beauveriabassiana as microbial pesticides with 15 chemical pesticides on the amount of microbes on the leaves of tomato plants. Results suggested that the alternating applications with chemical pesticides at intervals of approximately 7 days for the Bacillus formulation and approximately 3 days for the Beauveria formulation exerted no effect on the survival of the microbes derived from each formulation on the leaf surface. The alternating applications of Beauveria and captan agents should be considered, as some of them may affect the survival of the fungus.
The red-banded thrips Selenothrips rubrocinctus (Giard) was originally distributed throughout northern South America. This thrips attacks tropical fruits such as mango, cocoa, and guava in North America, Asia, and Central and South Africa. In Japan, it has been observed on mango and guava in Okinawa Prefecture, Amami-Oshima Island in Kagoshima Prefecture, the Ogasawara Islands in Tokyo Metropolis, and Kochi Prefecture; on Actinidia rufa in Miyazaki Prefecture; and on maple trees in Kyoto Prefecture. In late September 2022, damage caused by S. rubrocinctus was observed in sweet gum in Kyoto Prefecture, with gray or dark brown leaves. This is the first record of S. rubrocinctus occurring on sweet gum in Japan. The degree of damage to the leaves and the occurrence of adults and larvae of the thrips were investigated in sweet gum lining streets and road facilities in Kyoto Prefecture. Damage caused by the thrips to sweet gum was observed in areas south of Kameoka, and adults and larvae were detected in areas south of Nantan, Kyoto Prefecture.
Liothrips wasabiae (Thysanoptera: Phlaeothripidae) is an important insect pest of water wasabi (Eutrema japonicum). The area infested by L. wasabiae becomes black-spotted. Water wasabi requires a long cultivation period of approximately 1.5–2 years. However, chemical insecticides to control L. wasabiae can only be applied a maximum of three times according to the pesticide regulation. Therefore, two insecticides, dinotefuran and nitenpyram, that have been demonstrated to be highly effective, were investigated for their residual effect against L. wasabiae. Results showed that when adult L. wasabiae were released 28 days after insecticide treatment, dinotefuran caused a mortality of 56% compared to 10% with nitenpyram.
We investigated the seasonal occurrence of the rice stink bug, Niphe elongata (Hemiptera: Pentatomidae), in paddy fields and the ovarian development of females collected from fields in Shiga Prefecture, Japan. Early in August, when the rice ears of medium-maturing varieties emerged, adult bugs migrated to the paddy field, and the females laid eggs. The eggs hatched, and nymphs grew into adults. When late-maturing rice varieties started heading in late August, the adults entered the paddy field, and the females laid eggs. The eggs hatched, and the nymphs became adults. Therefore, in Shiga Prefecture, the life cycle of the rice stink bug produces two generations in 1 year. In September, no females had mature eggs in their ovaries, and adult bugs were believed to overwinter.
The rice bug, Leptocorisa chinensis (Hemiptera: Alydidae) is a pest insect that feeds on rice ears, resulting in pecky rice. We collected the eggs of rice bugs in grassland overgrown with gramineous plants on July 17 and 24, 2018, in the southern part of Shiga Prefecture, and then investigated the species of egg parasitoids. Four species of egg parasitoids, Hadronotus japonicus and H. nigricornis (Hymenoptera: Scelionidae) and Ooencyrtus nezarae and O. acastus (Hymenoptera: Encyrtidae), emerged from the eggs of rice bugs. Two species of wasps considered to be dominant, namely, H. japonicus and O. nezarae, exhibited high percentages of parasitism. Our study also recorded O. acastus parasitizing L. chinensis eggs for the first time in the literature.
We collected the adults of the rice bug, Leptocorisa chinensis (Hemiptera: Alydidae) from fields, from June to September in 2021 and 2022. We identified the species of tachinid flies parasitizing the adult rice bugs and investigated the seasonal changes in the parasitism rate. We also examined the parasitism of rice bug nymphs by tachinid flies. Adult bugs were confirmed to be parasitized by the tachinid fly, Clairvilliops breviforceps (Diptera: Tachinidae). The parasitism rate remained low throughout the survey period, reaching a maximum of approximately 23%. We could not clarify the parasitism of rice bug nymphs by the tachinid fly.
The frequency of pyrethroid- and neonicotinoid-resistant genes was investigated in the cotton aphid, Aphis gossypii Glover collected from watermelon fields in Inami Town, Wakayama Prefecture, in 2015, 2018 and 2022. The Aphis clone possessing the genes resistant to both insecticides occurred at a frequency of 19.5% in 2022. Low mortality rates for neonicotinoids and pyrethroids were observed in this clone.
This study investigated the effects of insecticides on the first instar larval and adult stages of the melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae) using two bioassay methods, leaf spraying and leaf dipping. The corrected mortality rates of the larval and adult stages for three insecticides (emamectin benzoate, abamectin, and pyridalyl) were 90%–100% in both methods. The corrected mortality rates of the larvae for most insecticides tended to be higher than those of the adults, except for two insecticides (emamectin benzoate and flonicamid).
We used the leaf-dipping method to determine the toxicity of 10 insecticides on the adult melon thrips, Thrips palmi, collected from Kanan Town and Tondabayashi City in Osaka Prefecture. Flometoquin and fluxametamide were effective against T. palmi. The toxicity of nitenpyram and emamectin benzoate depended on the collected population. Acetamiprid, spinetoram, abamectin, chlorfenapyr, cyantraniliprole, and pyridalyl showed low corrected mortality in all populations.
We identified spinosad-resistant populations of Frankliniella intonsa (Trybom) in strawberry greenhouses in Nara city and Kashiba city. The mortality rate of the Kashiba population for spinosad commercial concentration was 6.5%, but that of the Nara population was 86.2%. This suggested that F. intonsa collected from strawberry in Nara Prefecture developed resistance to spinosad.
The effects of the red-colored insect nets against Thrips tabaci Lindeman and T. nigropilosus Uzel were investigated in commercial carrot greenhouses, in Kyoto Prefecture. The degree of leaf damage caused by the thrips and their population density in the greenhouse with the red-colored insect net were lower than those with the white-colored insect net in October and November. T. tabaci and T. nigropilosus were primarily found in carrot greenhouses. T. tabaci was predominant among both group; however, the species composition of T. nigropilosus in the red-colored insect net group was higher than that of the control group. The red-colored insect nets were effective against T. tabaci, but the effectiveness against T. nigropilosus was undetermined.