In this study, we examined the practicality of organic tea production systems with 'Fushun' over two years and examined its effects on pest occurrence, soil, yield, and tea quality. The organic tea production systems with 'Fushun' suppressed the damage caused by Empoasca onukii Matsuda, Adoxophyes honmai Yasuda, Tetranychus kanzawai Kishida, Aleurocanthus camelliae Kanmiya & Kasai, Discula theae-sinensis (I. Miyake) Moriwaki & Toy. Sato, and Pestalotiopsis longiseta (Spegazzini) K. Dai & Tak. Kobayashi. Through the organic tea production systems with 'Fushun' yields were equal to those of conventional cultivation and were higher than those with 'Yabukita' at all tea harvesting seasons. In addition, the first-flush kabusecha of organic tea production systems had a higher nitrogen content in tea than that of conventional cultivation. In other seasons, the green tea quality was almost equal to the conventional cultivation with 'Yabukita' throughout the year.

The tea green leafhopper, Matsumurasca onukii Matsuda (Hemiptera: Cicadellidae), is one of the most serious insect pests of tea (Camellia sinensis (L.) O. Kuntze) in the major tea-producing regions of East Asia, including Japan, China, and Taiwan. The damage caused by leafhoppers leads to a significant decrease in tea production. Although control of tea green leafhopper is especially important in the organic cultivation of tea, there are currently no pesticides that can be used against the leafhopper in organic cultivation of tea. Natural pyrethrins have been reported to be effective against Empoasca fabae Harris, a species closely related to tea green leafhoppers. In this study, we performed field experiments to evaluate the control effect of natural pyrethrins to tea green leafhopper. As a result, the treatment with natural pyrethrin reduced the densities of M. onukii eggs, nymphs, and adults on tea shoots and the degree of feeding damage to the same level as chemical pesticides used in conventional control.

Tissue isolation was attempted with lesions of blister blight of tea to obtain colonies of Exobasidium vexans. After the ordinary surface sterilization method, colonies of E. vexans emerged from 13 leaf pieces in 180 leaf pieces examined (8.1%) collected in the Ashigara area, Kanagawa, Japan, on calcium–amended PDA. Fungal contamination occurred on 56.9% of the leaf pieces. Colony morphology of the tissue isolates was the same as that obtained from a mass basidiospore isolation. Colonies were composed of pseudohyphae and blastospores and gradually transformed to chlamydospore-like bodies (CLB) after 5 months. Germinability of CLB was tested by spreading a colony suspension on calcium–amended PDA. After 10 days incubation, CLB germinated and produced blastospores. Four germination types of CLB were categorized.

A climatological survey was conducted on the occurrence of frost damage to the first tea crop, which has been increasing since the end of the 20th century in Uji area of Kyoto prefecture. The occurrence of frost damage was concentrated in the first half of April and was closely related to the average temperature in March, which is an important factor in the early start of the budding period. It has been proven that when the average temperature in March is high (low), the budding period in April starts early (late). In particular, the frequency of occurrence of frost damage is extremely high on days in April with low temperatures of 0 ℃ or below after the average temperature in March was 8 ℃ or higher. Since 1990, the warming of the climate has been accompanied by an increase in temperatures in most months of the year. Particularly, one interesting tendency has been found that when the temperature in March is high there is a non-increasing or even decreasing tendency of temperature in April. This tends to create favorable conditions for frost damage. The long-term change in the seasonal progression of temperatures from March to April is likely to be related to the singular changes in the seasonal progression of atmospheric circulation over and around the Japanese islands associated with the recent global warming in the region.

I evaluated a method for estimating the population density of phytoseiid mites infesting commercial tea fields in Shizuoka Prefecture. The method employs a beating technique, where tea canopies are beaten onto a B5 white board to dislodge and collect mites infesting the leaves. A significant positive correlation was found between the mean numbers of these mites collected using the beating method and the level of infestation on hedge leaves, i.e., the number of mites and the rate of infested tea leaves. The distribution pattern in the field was analyzed using the data obtained from the beating method. I observed that the basic aggregation degree (α) was -0.0242, and the aggregation coefficient (β) was 1.03, indicating a random distribution (Poisson distribution). Additionally, I calculated the number of samples required for the target accuracy of D＝0.1-0.3 based on these α and β values. When the mean number of phytoseiid mites was one per sample, the beating method was applied at 11 points per field to achieve a target accuracy of D＝0.3. Furthermore, I examined the method for estimating the mean number of these mites based on their presence-frequency ratio or maximum abundance estimated using the beating method. A nonlinear regression equation, y＝1 - exp (-0.987x^0.985), was obtained for the relationship between their presence-frequency ratio (x) and mean value (y). Additionally, a linear regression equation, y＝0.408x, was obtained for the relationship between their maximum value (x) and mean value (y). In actual surveys, determining the presence-frequency ratios or maximum abundance of these mites in a preliminary survey, and then calculating the required number of samples based on the mean value estimated from these parameters, will enable a high-accuracy estimation of their population density.

Carbon stocks in the biomass of 28- or 29- and 40-year-old tea plants were investigated by measuring the dry biomass and total carbon content of each part of the tea plants (Camellia sinensis L. var. ‘Yabukita’), which have grown under the standard management in Shizuoka Prefectural Research Institute of Agriculture and Forestry, Tea Research Center. A linear regression analysis of the carbon stock in the tea leaves and branches above the standard pruning surface, which was assumed to be 50 cm above the ground of tea fields, provided a prediction of the carbon stock above the pruning surface as a function of the distance between the canopy and pruning surfaces. Based on the regression equation, the carbon stock in the upper aboveground part above the standard pruning surface of 30-year-old tea plants of the average plant height was estimated to be 4.81 t-C ha^-1. The carbon stocks in the lower aboveground part under the standard pruning surface and belowground part were estimated to be 14.0 and 12.5 t-C ha^-1, respectively. The total carbon stock of 30-year-old tea plants of the average plant height, i.e., the sum of above- and belowground parts, was estimated to be 31.3 t-C ha^-1. The carbon stock in the aboveground biomass under the pruning surface of 40-year-old tea plants was almost same as that of 28- or 29-year-old tea plants. The carbon stock in the belowground biomass of 40-year-old tea plants was significantly larger than that of 28- or 29-year-old tea plants.

Organic and inorganic components of Shishikui-kancha produced in midwinter in Kaiyo, Tokushima, Japan, were analyzed. Compared to tea produced in spring, the organic components of Shishikui-kancha were higher in free sugars and lower in polyphenols, catechins, caffeine, and free amino acids. In terms of inorganic components, Shishikui-kancha contained higher concentrations of Ca, Al, Mn, Ba and Sr than tea produced in spring.