• The Korean Journal of Pesticide Science
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• v.14 no.3
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• pp.241-246
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• 2010

Field experiments were carried out to establish economic threshold for com borer (Ostrinia furnacalis (Guen$\'{e}$e)) on waxy com plants by examining the number of adult insects caught in pheromone traps and the injury levels of waxy com which were artificially controlled. Adult com borers were lured into the pheromone traps during the whole growth period in five areas in Gangwon province including Chuncheon. The number of com borers trapped was the greatest in Chuncheon followed by Cheolwon and Hongcheon, and the same trend was observed for injury level of waxy com. Based on marketable yield data of waxy com plants related to the artificially-controlled injury levels at tassel stage, spray threshold was determined as the injury level of 11~15%, where the injury of com plants exceeded the economically admitting level.

• The Korean Journal of Pesticide Science
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• v.18 no.3
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• pp.175-180
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• 2014

This study was carried out to determine the economic injury level and economic threshold level on beet (Beta vulgaris L.) infested with Spoladea recurvalis in the plastic greenhouse condition in 2010. The second instar larvae of S. recurvalis were inoculated with 7 different density levels on the each 10 beet plants as a replication. Injury levels of beet leaves and density of S. recurvalis were increased with the inoculation density of S. recurvalis. However, yield and marketable commodity of beet were decreased. Linear relationship between the percent yield reduction (Y) of beet leaves and different infestation densities of S. recurvalis (X) was estimated by the following equation Y = 1.226x + 3.36. Based on the relationships between the densities of S. recurvalis larvae and yield index of beet leaves, the number of second instar larvae which caused 5% loss of yield, economic threshold level was estimated as 1.1 larvae/10 plants for the planting 10 days. The percent yield reduction (Y) of beet roots infested with different densities of S. recurvalis (X) estimated by the following equation Y = 1.537x + 1.4634 after inoculation for 10 days at 3rd harvesting of leaves. Based on the relationships between the densities of S. recurvalis larvae and yield index of beet roots, the number of second instar larvae which caused 5% loss of yield, economic threshold level was estimated as 6.4 larvae/10 plants for the planting 10 days.

• 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.

• Research in Plant Disease
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• v.12 no.3
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• pp.231-234
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• 2006

The influences of powdery mildew caused by Sphaerotheca fusca were assessed on cucumber to verify the economic injury level and yield response. Based on the relation of disease severity and yield response, economic threshold was determined by grading the disease severity of powdery mildew. Yield loss simulation due to damage of powdery mildew was conducted by defoliation of lower cucumber leaves in two seasons. The minimum number of leaves was 10 in spring season and 13 in autumn season which made no distinct difference on cucumber yield. The whole yields of cucumber was reduced as the disease severity was increased. Therefore occurrence of powdery mildew have a negative effect on cucumber yield. The regression equation between disease severity and yield loss showed Y=-57.237x+6143.1, $R^2=0.9628$. This equation suggests the disease severity of economic threshold is 17.6%, which is 3% reduction point of yield based on yield and economic relations. These results suggest that application of fungicide should be needed when 1 or 2 leaves of cucumber are infected by powdery mildew in the growing season.

• 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.45 no.3 s.144
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• pp.317-325
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• 2006

According to the preceding survey on insect pests of the green perilla, Perilla frutescens var. japonica HARA, The major pests were Aphis egomae Shinji, Pyrausta panopealis (Walker), Tetranychus urticae Koch, Polyphagotarsonemus lotus Banks, Tetranychus kanzawai Kishida at Guemsan, Chungnam, 2004. Aphis egomae causes nearly 100% injury of the green perilla in uncontrolled green houses. A field study was conducted to estimate economic injury levels (EILs) and control thresholds (CTs) for A. egomae injuring green perilla in green houses. Different densities of A. egomae ranged from 1 to 80 aphids per 100 plants in early inoculation. The mean injurying rate of plant was 2.4% to 40.5% at the end of June at differently inoculated levels. The economic loss time calculated by the ratio of cost managing aphid to market price (C/V) (C: cost managing aphid, V: Market price) in early season (from May to 13. June) was 5.8% and in peak season (from 13. June to 30. June) was 9.3%. Economic injury level in early and peak season was 5.3 aphids per plant and economic injury levels in peak season were 0.6 aphids per plant and 7.6% injured rate of plant. The control thresholds calculated by 80% level of economic injury level in peak season were 0.5aphids per plant and 6.1% injury rate of plant, respectively.

• Research in Plant Disease
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• v.19 no.3
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• pp.196-200
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• 2013

This study was carried out to investigate yield loss due to soybean leaf spot disease caused by Cercospora sojina Hara and to determine the economic threshold level. The investigations revealed highly significant correlations between disease severity (diseased leaf area) and yield components (pod number per plant, total grain number per plant, total grain weight per plant, percent of ripened grain, weight of hundred seed, and yield). The correlation coefficients between leaf spot severity and each component were -0.90, -0.90, -0.92, -0.99, -0.90 and -0.94, respectively. The yield was inversely proportional to the diseased leaf area increased. The regression equation, yield prediction model, between disease severity (x) and yield (y) was obtained as y = -3.7213x + 354.99 ($R^2$ = 0.9047). Based on the yield prediction model, economic injury level and economic threshold level could be set as 3.3% and 2.6% of diseased leaf area of soybean.

• 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.

• 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.