We investigated parasitism of the tea spiny whitefly Aleurocanthus camelliae Kanmiya & Kasai by the parasitoid Encarsia smithi (Silvestri) in 121 tea fields in Shizuoka Prefecture, Japan, from Dec. 2012 to Mar. 2013. The parasitism rate ranged from 0% to 92.3%, with a mean of 29.1%. Thirty of the fields had rates of parasitism ranging from 10% to 20%, whereas 16 fields contained no parasitized whitefly. Although a comparison of E. smithi parasitism among six different areas failed to reveal clear differences, the parasitism rate in the Maki-no-hara area, where A. camelliae was recorded for the first time in Shizuoka Prefecture, was significantly higher than that in the central area. The relationship between the densities of A. camelliae and the rate of E. smithi parasitism showed a negative correlation, suggesting that the density of A. camelliae in tea fields is influenced by E. smithi parasitism.
The color of made tea is one of the most important factors for evaluating tea cultivars or lines. In the present study, we investigated the relationship between the sensory test score of color and the measured color space unit of hue angle (h*), pigments, and pH value for objective evaluation of line selection. The experimental results showed that the sensory test score of color had a significant correlation with the measured color space unit of h* value and the conversion rate of chlorophyll into pheophytin. The pH value of made tea also had a positive correlation with the sensory test score, because a lower pH would induce a higher pheophytin conversion rate. Although the h* value of fresh tea leaves had a high correlation with that of made tea in the first tea crop season, a low correlation was found with the second tea crop. Thus, there may not be a matching relationship between the color of fresh tea leaves and that of processed tea leaves. In conclusion, measurement of the h* value, conversion rate of chlorophyll into pheophytin, and pH value would be useful in the evaluation of tea cultivars and lines.
Sen-cha flavor is generally produced during the manufacturing process and that suitable conditions result in a high-quality flavor. The roasting process is known to be the most important step for generating the characteristic Sen-cha flavor. The scope of this research is to identify the key odorants in Sen-cha caused by roasting. An aroma extract dilution analysis (AEDA) has been applied to the volatile fractions isolated from Sen-cha (tea leaves), which was roasted by using a drum roaster. AEDA revealed that twenty odorants increased, and two odorants decreased by roasting. Among of these odorants, 4-mercapto-4-methyl-2-pentanone, 2-ethyl-3,5-dimethylpyrazine and furaneol were detected as potent odorants caused by roasting. On the other hand, (Z)-3-hexenal and (E,E)-2,4-heptadienal were decreased by roasting. The characteristic flavor of Sen-cha caused by roasting depends on the type of roaster, condition and material. Therefore, data accumulation would be necessary to clarify the characteristic flavor of Sen-cha in greater details.
Characteristic off-flavor derived from the so-called “Natsucha-shu” is one of the major problems in summer crop of green tea. Until now, the authors made a finding that a low-temperature (19℃) storage of fresh tea leaves before steaming (LTS) improved the off-flavor of “Natsucha-shu”. Therefore, the scope of this research is to elucidate “Natsucha-shu” improvement caused by the LTS. An aroma extract dilution analysis (AEDA) has been applied to the volatile fractions isolated from the sen-cha, processed through the LTS. AEDA have revealed that (Z)-1,5-octadien-3-one，2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, (E,Z)-2,6-nonadienal, 3-methylnonane-2,4-dione and furaneol were detected as prevalent odorants in sen-cha with “Natsucha-shu”: while 4 odorant, namely, linalool, β-damascenone, (Z)-methyl jasmonate, indole were potent odorants present in sen-cha, processed through the LTS without “Natsucha-shu”. The semi-quantitative analysis and additive test of odorants clarified that methoxypyrazines as causing agents of “Natsucha-shu” were stable during the LTS, and increased odorants caused by the LTS would be a capable of masking the “Natsucha-shu”.
We examined the toxicity of 19 insecticides, 7 acaricides, and 7 fungicides as dips for the pupae of Trichogramma dendrolimi, which parasitizes the eggs of Homona magnanima. Most insect growth regulating (IGR) insecticides, acaricides, and fungicides were harmless to pupae of T. dendrolimi. Some of the pesticides such as neonicotinoids, acephate, emamectin benxoate, chlorfenapyr, and milbemectin that were harmful to adults of T. dendrolimi were harmless to pupae because the pupae were protected by the H. magnanima eggshells. However, profenofos, chlorpyrifos, and spinosad were harmful and their mortality of treated pupae were 90.6%, 73.3%, and 97.1%, respectively.
New technologies for the removal of volcanic ashes adhered to new shoots of tea plants were examined. The percentage of volcanic ash extraction with cyclone equipment was 60-75%. A tea -picking machine with a volcanic ash removal function removed about 60% of the ashes. A sprinkler in a tea garden removed volcanic ashes from about 80% of the shoots by watering at a rate of 30t per 10a. The volcanic ash extraction ratio of these new machines is superior to the machine used in the conventional method.
In recent years, the content of available phosphate and exchangeable potassium in the soil of Japanese tea gardens has been increasing. Especially the amount of available phosphate in the soil has far exceeded the permissible level. These excessive accumulation of minerals in the soil may have been caused by the following factors: 1) phosphate fertilizer applied to the soil surface would not easily leach to the subsoil, 2) potassium is supplied by the decomposition of leaves and stems add to the soil by periodical pruning, and 3) specified amount of fertilizer is applied only the between-row spacing (about 20% of tea garden area). When considering the cost of fertilizer application, the amount of fertilizer should be determined based on the mineral concentrations in the soil. In order to easily determine the mineral concentration in the soil without cost increase, we used a hand-made colorimeter equipped with different wavelength LED, together with a commercial water analysis kits. In this analysis, 0.002 N H2SO4 was used as an agent extracting available phosphate and exchangeable potassium. This analysis procedure can easily detect the excessive levels of available phosphate and exchangeable potassium in the soil with sufficient accuracy.
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