Jang-Jeon Choi

Frostfall Forecasting in the Naju Pear Production Area Based on Discriminant Analysis of Climatic Data

In order to predict frostfall, nocturnal cooling rate and air temperature changes were analyzed on days with and without frost when the maximum temperature was lower than . In general, the nocturnal cooling rates on frosty days were higher than those on non-frosty days. The cooling rates averaged from 19:00 to 24:00 on frosty and non-frosty days were and respectively. As expected, the nocturnal temperature on frosty days was lower than that on non-frosty days. Especially, the midnight air temperature averaged about on frosty days, which was lower than that on non-frosty days (i.e., ). The discriminant analysis using three independent variables (i.e., total cloud amount, air temperature at 24:00, and 5-day rainfall amount) successfully classified the presence of frost with 87% accuracy.

Control of Soilborne Fungal Diseases on Muskmelon by Soil Disinfestation in Consecutively Cultivated Fields

This study was carried out to determine the causal agents of soil-borne fungal diseases that pose a threat to the muskmelon production in Cheong Yang, Korea and to investigate the potential effects of hot water drenching and three fumigant (metam sodium, dazomet and methyl bromide) on these diseases. As the agents of the diseases, Monosporascus cannonballus, Didymella sp., Fusarium sp., Phytophthora sp., were detected. Hot water and the fumigants were treated on two successive cropping seasons of melon. Soil temperature was measured at 0, 10, 20 and 30 cm soil depth. In 2005, soil sterilization by hot-water was more effective significantly to control of the diseases than by fumigant. yield was the highest in hot-water sterilized plot as . Dazomet () treated plot was followed as . In 2006, hot water sterilized plot showed higher yields than non-treated plots (). But the other three fumigant contained Dazomet () were no difference (P

Monitoring thrips species with yellow sticky traps in astringent persimmon orchards in Korea

Thrips are one of the insect pests of persimmon (Diospyros kaki Thunb.) in the major production areas of astringent persimmon in Korea. We surveyed astringent persimmon orchards in the Damyang, Sangju and Cheongdo regions of Korea to determine thrips species composition and abundance. Orchards sprayed with either organic or conventional pesticides were sampled over the course of one flowering season, using yellow sticky traps to determine if this is a suitable method for monitoring thrips populations, and to determine thrips species composition and abundance. Eight thrips species were captured on yellow sticky traps in both the tree canopy and ground cover: Ponticulothrips diospyrosi Haga et Okajima, Scirtothrips dorsalis (Hood), Frankliniella occidentalis (Pergande), F. intonsa (Trybom), Thrips tabaci (Lindeman), T. hawaiiensis (Morgan), T. coloratus (Schmutz) and T. palmi (Karny). In all regions, F. occidentalis and F. intonsa dominated in both organic and conventional orchards. S. dorsalis, F. occidentalis, F. intonsa and T. hawaiiensis were found in persimmon flowers, with S. dorsalis the dominant thrips. Significantly more S. dorsalis were captured from flowers in the lower and middle canopy than in flowers from the upper canopy. Fruit damage was also significantly higher in fruit from the lower canopy than in fruit from the middle and upper canopy.

Comparision of Growth Characteristics andProductivity of Young Trees of a New Cultivar‘Manpungbae’ Trained to Trellis Systems

One-year old pear (Pyrus pyrifolia L.) trees of a new commercial cultivar ‘Manpungbae’, recently developed in South Korea, were planted in 2001 (planting year 1) and trained to four trellis systems: Y-trellis, Y-II-trellis, pergola, and vase-pergola. To evaluate training systems in the local area (southern Korea), tree growth responses were compared for each trellis system from planting years 3 to 8. For trees trained to Y-trellis and pergola systems, a high proportion of land covered by tree canopy was maintained over the study duration, with 70–80% coverage in year 8. Eight-year cumulative yield per tree was increased in the vase-pergola system with a low planting density and an additional scaffold. Compared with other systems, cummulative yield use efficiency was greatest in Y-II-trellis and pergola systems in years 5 and 8. Compared with Y-II-trellis and vase-pergola systems, the 8-year cumulative yield per hectare was two fold greater for trees trained to the Y-trellis (103 tons) and pergola systems (101 tons). Use of the pergola system improved average fruit weight and fruit soluble solid contents, as well as net income in year 8. Given that we observed reduced fruit productivity and increased labor hours (pruning and orchard work), we consider the Y-trellis and pergola systems to be less valuable trellis systems than the others evaluated.

Freezing Hardiness of Several Pear Cultivars According to Degree and Duration of Low Temperatures

Freezing hardiness of winter bud and branch of several pear (Pyrus pyrifolia) cultivars according to degree and duration of low temperatures was investigated by sprouting, electrolyte leaching rate and triphenyltetrazolium chloride (TTC). Sprouting rate as infected by degree and duration of low temperature were different between cultivars. The lower temperature, the longer duration, sprouting rate was decreased. Electrolyte leaching rate was showed above 30% at below treatment regardless of cultivars and duration. The lower temperature and the longer duration, Electrolyte leaching rate was increased. Electrolyte leaching rates of Manpungbae, Niitaka and Chuwhangbae at for 9 hours treatment which were observed high sprouting rate, were lower than those of other varieties. Absorbance rates by TTC test at treatment were 66.0 to 96.5% for 6 hours, 49.4 to 91.9% for 9 hours, and 37.3 to 89.4% for 12 hours. Freezing hardiness of pear cultivars at ecodormancy was different according to degree and duration of low temperature treatments.

Growth and fruit production of asian pear trees grown on Y-, T-, and vase-training systems

This study was carried out to evaluate the effects of training systems on growth and fruit production of ‘Niitaka’ pear (Pyrus pyrifolia L.) trees in the first 8 years in South Korea. The training systems included Y-trellis (YT), T-trellis (TT), and vase-pergola with either two (VP I) or three main branches (VP II). Tree spacing for YT, TT, VP I, and VP II were 6.5 m between tree rows, and 3.0, 6.0, 3.0, and 6.5 m between trees, respectively. The TT trees had lower tree height, canopy area, and number of new shoots, average length of new shoots, and trunk cross sectional area as compared to those in other training systems in year 3 or year 8. The TT and VP II systems were slow to fill the allotted space from year 3 to 8. The VP I trees had comparatively rapid development of the tree canopy, high cumulative yield efficiency per tree, high cumulative fruit yield per area, and large fruit size, as well as low operation hours for orchard management. Fruit quality parameters, such as fruit shape, soluble solids content, firmness, and titratable acidity, were not consistently affected by training system in years 5 and 8.