• Korean journal of applied entomology
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• v.47 no.4
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• pp.407-411
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• 2008

This study was conducted to estimate the economic injury level (EIL) and economic threshold (ET) of the green peach aphid, Myzus persicae, on Chinese cabbage (Brassica campestris var). The changes of biomass of Chinese cabbage and M. persicae density were investigated after introduction of M. persicae at different density (0, 2, 5, 10, 15, and 20 per plant; inoculated at 10d after planting). The densities of M. persicae largely increased from the above initial densities to 0, 92.3, 177.4, 406.9, 440.4, and 471.3 aphids per plant at 18d after the initial inoculation, respectively. The biomass of Chinese cabbage significantly decreased with increasing the initial inoculated density of M. persicae: 602.0, 264.2, 262.0, 109.3, 151.0, and 67.3 g in above plots with different initial densities, respectively. The relationship between cumulative aphid days (CAD) and yield loss (%) of Chinese cabbage was well described by a nonlinear logistic equation. Using the estimated equation, EIL of M. persicae on Chinese cabbage was estimated 25 CAD per plant based on the yield loss 13%, which take into account of an empirical gain threshold 5% and marketable rate 92% of spring Chinese cabbage. Also, ET was calculated at 80% of EIL: 20 aphids per plant. Until a more elaborate EIL-model is developed, the present result may be useful for M. persicae management at early growth stage of Chinese cabbage.

• Korean journal of applied entomology
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• v.50 no.4
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• pp.289-293
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• 2011

This study was conducted to develop economic injury level (EIL) of onion thrips, Thrips tabaci, on welsh onion (Allium fistulosum L. var) in the early transplanting stage. The changes of welsh onion biomass, yield loss, and T. tabaci density were investigated according to the inoculation periods of T. tabaci. In the early transplanting stage of welsh onion, the yield loss (%) increased with increasing inoculation periods: 17.0, 53.3, 38.4, and 80.8% yield loss in 5, 10, 15, and 20 d inoculation periods, respectively. The relationship between Cumulative Insect Days (CID) of T. tabaci and yield loss (%) of welsh onion was well described by a nonlinear logistic equation. Using the estimated equation, EIL of T. tabaci on welsh onion was estimated to 30 CID per plant based on the yield loss 12% (an empirical gain threshold 5% + marketable rate 93% of welsh onion). ET was calculated to 24 CID, which corresponds to 80% of EIL. Until a more defined EIL-model is developed, the present results should be useful for T. tabaci management in early growth stage of welsh onion. The effect of T. tabaci attack on the yield of welsh onion in late growing season (120 days after transplanting) was also examined. The yield of welsh onion increased at a low population density of T. tabaci and decreased at higher densities, showing a typical over-compensatory response.

• The Korean Journal of Pesticide Science
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• v.18 no.3
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• pp.196-201
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• 2014

This study was conducted to develop economic injury level (EIL) of sweet potato whitefly, Bemisia tabaci, on oriental melon. In greenhouse, seedlings of oriental melon were transplanted at June 8, 2010 and we inoculated adult B. tabaci with the density of 0, 1, 5, 10, or 20 per ten leaves at July 14. Adult of B. tabaci increased approximately twenty five-fold at 60 days after inoculation in the plot of 20 adults per ten leaves. The damages on leaves and fruits by B. tabaci were started to appear at 20 days after inoculation, and the damage rates of leaves or fruits were 28.5 or 31.5 percent at 60 days after inoculation, respectively, in the plot of inoculation with 20 adults per ten leaves. The yield of oriental melon was reduced as the inoculation density of B. tabaci increased, and the relationship between inoculation density of B. tabaci and the rate of damaged fruit could be described by a linear regression Y = 0.961x + 0.0562 ($R^2$ = 0.976). Based on the relationship, the economic injury level was 5.1 adults of B. tabaci per leaf and the control threshold estimated by 80% level of economic injury level was 4.1 adults per leaf for control of sweet potato whitefly.

• Korean journal of applied entomology
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• v.54 no.1
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• pp.1-6
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• 2015

This study was conducted to estimate the economic injury level (EIL) to leaf broccoli (leaf vegetable) by the diamondback moth (Plutella xylostella L.) in 2007 and obtain basic data for pest management. To investigate the relationship between initial density of diamondback moth larvae and broccoli leaf yield, experimental plots with five treatments (0, 0.5, 1.0, 1.5 and 2.0 larvae per plant) as initial density were established. We inoculated larvae on cheesecloth covering to survey changes in larval density. When grown for consumption, leaves of broccoli are harvested in periods. High levels of larvae were associated with significant reductions in leaf yield. There were 0%, 15%, 35%, 42%, 44% yield reductions due to a density of 0, 0.5, 1.0, 1.5, 2.0 diamond back moth larvae per plant, respectively, 25 days after larva inoculation. The regression equation used to predict leaf yield based on the number of initial larvae per plant was y = 1636-394x($R^2=0.79^{***}$>). EIL of the diamondback moth on leaf broccoli was 2~3 larvae per 10 plants for a damage level of 5%. The economic threshold was 1~2 larvae per 10 plants. Thus, diamondback moth management should be initiated when 1~2 larvae appear on 10 plants.

• Korean journal of applied entomology
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• v.48 no.2
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• pp.237-243
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• 2009

This study was conducted to develop economic injury level (ElL) and economic threshold (ET) of Cabbage armyworm, Mamestra brassicae L. on cabbage (Brassica oleracea L. var). The changes of cabbage biomass and M. brassicae density were investigated after introduction of larval M. brassicae (2nd instar) at different densities: 0, 1, 2, 4, 8, and 16 larvae per plant at 40 d after planting for an open field experiment, and 0, 2, 5, 8 and 12 larvae per plant at 25 d after planting for a glass house experiment. In the field experiment, the yield loss of cabbage was not significantly different among treated-plots at 30 d after the larval introduction, showing an over-compensatory response of cabbage plants to M. brassicae attack. In the glasshouse experiment, however, the biomass of cabbage at 15 d after the larval introduction significantly decreased with increasing the initial introduced number of M. brassicae, resulting in 38.3, 36.7, 21.7, 23.3 and 16.7g in above treated-plots, respectively. The relationship between cumulative insect days (CID) and yield loss (%) of cabbage was well described by a nonlinear logistic equation. Using the estimated equation, ElL of M. brassicae on cabbage was estimated at 44 CID per plant based on the yield loss 14%, which take into account of an empirical gain threshold 5% and marketable rate 91% of cabbage. Also, ET was calculated at 80% of the EIL: 35 CID per plant. Until a more elaborate EIL-model is developed, the present result may be useful for M. brassicae management at early growth stage of cabbage.

• Korean journal of applied entomology
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• v.53 no.2
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• pp.93-96
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• 2014

This study was conducted to determine the economic injury levels and control thresholds for the striped cabbage flea beetle, Phyllotreta striolata (Coleoptera: Chrysomelidae), on Chinese cabbage at two different planting times. The number of inoculated adults per 10 cabbages was 0, 2, 4, 8, and 16 at the early developmental stage of the cabbage5 days after planting) and 0, 10, 20, 30, and 40 at the middle developmental stage (30 days after planting). Damages to the leaves at the first inoculation were 2.5-21.1% and at the second inoculation were 1.8-26.3% after harvesting. The linear relationships between population density and yield reduction were as follows: Y = 1.3475X + 2.135 ($R^2$ = 0.8699) at the early developmental stage and Y = 0.703X - 1.78 ($R^2$ = 0.966) at the middle developmental stage. On the basis of these results, the economic injury levels caused 5% loss of yield; there were 2.1 adults per 10 Chinese cabbage at the early developmental stage and 9.6 adults per 10 Chinese cabbage at the middle developmental stage.

• Korean journal of applied entomology
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• v.50 no.3
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• pp.215-220
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• 2011

This study aimed to estimate control thresholds for managing common cutworm, Spodoptera litura Faricius (Lepidoptera: Noctuidae) at different larval densities and growth stages of Chinese cabbage in field conditions. The percent yield reduction (Y) of Chinese cabbage infested by different densities of S. litura (X, no. of larvae/100 plants) for three weeks were estimated by Y=-21.85X+1300 (R2=0.997) 5 days after transplanting and Y=-12.1X+1382 (R2=0.998) 20 days after transplanting. Based on the relationships between the densities of S. litura larvae and the yield index of chinese cabbage, the number of larvae (2nd to 3rd instar) which caused 5% loss of yield was estimated as 2.9/100 plants 5 days after transplanting, and 5.6/100 plants 20 days after transplanting.

• Korean journal of applied entomology
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• v.48 no.1
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• pp.81-86
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• 2009

Economic injury level and control thresholds for the management of beet army worm, Spodoptera exigua (Lepidoptera: Noctuidae) were evaluated on chinese cabbage of two different planting time. Two inoculation times were tested for each planting and the number of inoculated larva was 10, 20, 40, 80, respectively. Damages of leaves by first inoculation were 63.2% after eight days planting on 80 larva inoculation plot. By the second inoculation, those were below 50% after 20 days planting on the end of September. The linear relationships between population density and yield reduction were as following; Y = -10.62x + 867.9 ($R^2\;=\;0.643$) for 5 days and Y=-6.432x + 1074 ($R^2\;=\;0.720$) for 20 days. Based on these results the economic injury level was 5.4 larva for five days and 9.0 larva for 20 days per 20 chinese cabbage. The control thresholds calculated by 80% level of economic injury level were 4.3 and 7.2 larva, respectively.

• Research in Plant Disease
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• v.12 no.3
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• pp.164-167
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• 2006

Potential factors favoring black stains during fruit development in Pyrus serotina was investigated. Black stain occurred from young fruit till harvest. The color of the affected fruits in early stage was black or light reddish brown, but turned to light brown over time. Fruit bags with lower light transmission and inner bags with poor aeration stimulated the symptoms, and high water permeability of the bags increased the black stain. Much rain and/or poor light transmission and aeration within the canopies also favored the occurrence of black stain. Diminution of pathogenic fungi density by lime sulfur was more effective than the canopy spray of fungicide for the prevention of black stain.

• Korean journal of applied entomology
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• v.47 no.4
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• pp.401-405
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• 2008

This study was conducted to estimate the control thresholds (CTs) of imported cabbage worm, Artogeia rapae L., injuring Chinese cabbage. The second instar larvae of A. rapae were inoculated with five density levels on each Chinese cabbages transplanted three weeks earlier under greenhouse condition, and checked injury rates after allowing their feeding for one week and two weeks, respectively. The average leaf area consumed by single larvae was 657.7 $mm^2$ in plots inoculated at three weeks after transplanting (WAT) and 2495.8 $mm^2$ in plots at 6-WAT, respectively. In the field experiment, different numbers of A. rapae ranged from one to seven larvae were inoculated on 20 plants. The percent yield reduction (Y) of Chinese cabbage infested by different densities of A. rapae (X) for a three-week period was estimated by the following equation; (1) Y=1.764X-0.3049 ($R^2$=0.9901) in plots inoculated at 3-WAT; and (2) Y=1.0305X-0.2976 ($R^2$=0.9398) in plots inoculated at 6-WAT. Based on the relationships between the densities of A. rapae larvae and the yield index of Chinese cabbage, the number of second instar larvae which caused 5% loss of yield (gain threshold proposed by Japan), was estimated as 3.0 per 20 plants for the 3-WAT and 5.1 for the 6-WAT.