Covering cultivation is a critically important method for high quality powdered green tea production. The covering period, once a year previously, becomes twice a year with drastically increasing demand for powdered green tea since around 2000. Therefore, there is a fear of some damage to the tea tree by decreased growth due to insufficient photosynthesis. This research was conducted for five years to examine the effect of covering periods in a year on the growth of tea shoots and the canopy surface temperature based on thermal images. As prolongation of covering period in a year, decreased growth, and higher temperature on the canopy surface in midsummer were observed, since the 2nd year of direct covering cultivation, and since the 3rd year of ceiling-shelf covering cultivation, indicating that the difference in the covering methods has influences on the growth of tea tree over several years. Our results suggested possibility of detecting accumulative damage to the tea tree caused by excessive covering period, based on thermal images of the canopy surface.
In search of chemical agents effective for adult control of the yellowish elongate chafer, Heptophylla picea Motschulsky (Coleoptera: Scarabaeidae), pesticidal activities of neonicotinoids and diamide insecticides were tested in multiple application forms and under various equipment/environmental conditions. Laboratory tests of adults which were dipped directly into the solutions of the insecticides or reared on soybean plants sprayed with insecticides both showed high activities of the neonicotinoids, thiamethoxam and clothianidin, suggesting the possibility of effective adult control with oral dosing e.g. seed treatments on a companion plant. Other neonicotinoids such as dinotefuran were less active to the adult chafers. As for the diamide insecticides, cyclaniliprole and cyantraniliprole were comparable to fenitrothion (MEP) in their oral toxicities, but scarcely showed contact toxicity in the rearing tests; the effective application forms of those chemicals must be surveyed in future studies.
Odorants in aroma extracts isolated from fresh tea leaves change as tea leaves grow. Elucidation of these changes with tea leaf maturity is essential for the cultivation, manufacturing, and quality control. Aroma volatiles were extracted from fresh tea leaf samples using the solvent-assisted flavor evaporation technique (10-3 Pa). An aroma extract dilution analysis applied to the volatile fractions revealed hexanal, (Z)-3-hexenal, (Z)-1,5-octadien-3-one, (Z)-3-hexenol, 2-isopropyl-3-methoxypyrazine and 2-isobutyl-3-methoxypyrazine were detected with high flavor dilution (FD) factors. These 6 compounds increased with tea leaf maturity, as confirmed by the gas chromatography – mass spectrometry. On the other hand, two other odorants, coumarin and vanillin, were detected with low FD factors and decreased with leaf maturity. This result would be a good contribution to the improvement of cultivation and manufacturing technology, as well as quality control of tea.
The population of sika deer, in Shiga Prefecture, has increased recently. It is said that the deer have caused damage to tea fields in Koka City (a major tea-producing area in Shiga Prefecture). However, we cannot understand the situation in detail. For this reason, we conducted a questionnaire survey for farmers in July 2016, and we did a tea field survey from September 2016, as well.
Firstly, the results of the questionnaire survey showed approximately 60% of the farmers recognized that sika deer have been a bad influence in young arboretums, and approximately 90% of the farmers recognized this in mature orchards.
Secondly, the results of field surveys showed that invasion by the sika deer have fed on the undergrowth in the tea fields. But, in late October (the amount of undergrowth had become less), and we often saw sika deer feeding on the tea leaves.
In addition, many farmers asserted that applied organic fertilizer attracts sika deer to tea fields, Thus, we researched the feeding habits of sika deer, and as a result, we saw aggressive foraging behavior of sika deer in tea fields to organic fertilizer (for instance, rapeseed oil cake and fish meal). However, the sika deer did not feed on castor oil cake during the observation.