The role of Chinese cabbage as a trap crop

The role of Chinese cabbage as a trap crop forflea beetles (Coleoptera:Chrysomelidae)in production of white cabbageStanislav Trdan *,Nevenka Valicˇ,Dragan Z ˇnidarc ˇic ˇ,Matej Vidrih,Klemen Bergant,Emil Zlaticˇ,Lea Milevoj University of Ljubljana,Biotechnical Faculty,Department of Agronomy,Chair of Entomology andPhytopathology,Jamnikarjeva 101,SI-1111Ljubljana,SloveniaReceived 7April 2004;received in revised form 27October 2004;accepted 7March 2005AbstractDuring the years 2002and 2003,preference of flea beetles,Phyllotreta spp.,to white and Chinesecabbage,grown in monoculture and in mixed crop,was tested.The aim of the research was todetermine if Chinese cabbage is an appropriate trap crop for this pest in the production of whitecabbage,an important vegetable in Europe and in North America.The number of beetles on Chinesecabbage in monoculture and in mixed crop did not differ significantly.In both treatments the numberof adults of flea beetles on Chinese cabbage and the percentage of damaged leaf area they caused,were significantly higher than that on white cabbage.Statistically significant and positive correlationwas established between leaf damage and number of flea beetles.It was stronger in 2003,which wasless favorable for the crop with regards to the weather conditions (drought and high air temperatures).No significant differences were found in the number of adults and in most evaluations also in thedamage assessments on white cabbage when grown in monoculture and in mixed culture.Therefore,we concluded that Chinese cabbage grown in mixed crop with white cabbage is not a suitable controlmeasure for reducing the damage caused by flea beetles.#2005Elsevier B.V .All rights reserved.Keywords:Phyllotreta spp.;Trap cropping;White cabbage;Chinese cabbage;IPM/locate/scihortiS.Trdan et al./Scientia Horticulturae106(2005)12–2413 1.IntroductionFlea beetles,Phyllotreta spp.,are among the most important pests of cultivated brassicas in Europe and North America(Stoner,1992;Ester et al.,2003).Beetles can cause substantial damage on host plants by feeding on the leaves,especially in early stages of development(Palaniswamy and Lamb,1992).In Central Europe and in continental parts of Southern Europe,brassicas are planted in openfields in the beginning of May(early white cabbage varieties),which usually coincides with high population densities offlea beetles.Prevalent species offlea beetles are Phyllotreta nemorum L.,Phyllotreta undulata Kutschera,Phyllotreta cruciferae Goeze,and in some districts also Phyllotreta vittula(Redtenbacher).In these areasflea beetles usually have one generation per year(Vig,2000)and prevail in the open until temperatures are too low(end of October).Flea beetles cause less damage to older plants,because these plants can‘resist’the pest with greater leaf surface.Beside causing a direct damage,flea beetles can also be a vector for some plant pathogens(Dillard et al.,1998;Stobbs et al., 1998).Seedlings of late white cabbage(Brassica oleracea L.convar.capitata[L.]Alef.var. alba DC.)varieties in Europe are planted in openfields from the beginning of July and can also be important hosts toflea beetles.Beetles cause more damage in warm season, when they feed more intensively,thus compensating a loss of water.Due to climatic changes the hot season has been prolonging and average temperatures are higher than they were few decades ago,which can also influence the pest bionomics(Yamaguchi et al.,2001;Fuhrer,2003).Brassicas seedlings can hardly recover from severe attack by flea beetles,thus the use of insecticides is still the most common pest control strategy applied in the early stages of plant development in white cabbage production. Consequently,flea beetles have developed resistance to most of insecticides(Turnock and Turnbull,1994).To reduce the use of pesticides,new environment friendly methods of pest control are being developed.In the past20years,considerable research has been done in thefield of intercropping,and it has become an important part of integrated pest management(IPM)in many places(Finch and Kienegger,1997;Held et al.,2003).Compared with intercropping, trap cropping is a less investigated method of an environment friendly pest control (Boucher et al.,2003;Smyth et al.,2003).In this method trap plants(plants to which pests are more attracted)are planted among the main crop.Pest populations on trap plants are more numerous and so only these plants are treated with insecticides.The quantity of pesticides is thus reduced,as well as the pest population.Beside direct influence(pests are more susceptible to a trap plant),trap cropping and intercropping also have an indirect impact:in mixed crops the level of parasitism is usually higher(Hokkanen,1989),which also reduces the damage.In the literature some efficient models of trap cropping are reported(Asman,2002;Rea et al.,2002),though a combination of white cabbage and Chinese cabbage(Brassica pekinensis[Lour.]Rupr.),both very popular vegetables in Europe,was not stated.Out of practical experiences it is known thatflea beetles cause more damage on Chinese cabbage than on white cabbage(Kinoshita et al.,1979).As the growth and development of Chinese cabbage and late white cabbage varieties coincides,the suitability of Chinese cabbage as atrap plant for flea beetles in mixed crop with white cabbage was investigated in our study.Our hypothesis was that the Chinese cabbage,as a trap plant,diverts the beetles from whitecabbage plants and thus reduces the damage caused by the beetles.To test the hypothesis,differences between susceptibility of flea beetles to white cabbage and Chinese cabbage inmixed crop and in monoculture crop were evaluated together with the differences in theextent of damage on leaves.2.Materials and methods2.1.Plant material and insectsA 2-year experiment (2002–2003)was carried out in the field (Biotechnical Faculty inLjubljana,Slovenia,468040N latitude,148310E longitude,300m above sea level,UTM33TVM50).Different brassicas,mostly white cabbage,have been grown on this locationfor many years for research purposes,therefore population of flea beetles,Phyllotreta spp.,there is permanent and numerous.2.2.AgrotechniqueThe site was a heavy clay soil with 2.6%organic matter content and 6.8pH.The climate at the site is a temperate continental.Seedlings of white and Chinesecabbage were seeded in cell trays,one seed per cell (volume 33cm 3),filled withcommercial peat lite mix (1:1,v:v).The trays were placed in a greenhouse for 30days,watered each morning and fertilized once a week with Peter ’s soluble 20-20-20(N –P 2O 5–K 2O).Experimental plots were prepared with a rotary tiller cultivator.The seedlings weretransplanted on 1August 2002and on 4September 2003into raised beds mulched withblack polyethylene (15m m thick).Beds were 1.3m wide Â15cm high,with 1.8mbetween the centers of contiguous beds.In both years,the previous crop was lettuce.General agricultural procedures used in commercial brassicas production were followedfor both years,except the use of insecticides.Fertilizer was supplied in three splitapplications of N,for a total of 240kg ha À1,and a single application of P 2O 5and K 2O atland preparation,for a total of 320and 400kg ha À1,respectively.The irrigation systemconsisted of trickle-irrigation tubing laid on the bed.Irrigation for each treatmentwas supplied by a combination of drip irrigation and natural rainfall,according toevapotranspiration data.Water amounts were controlled for all treatments withtensiometer.2.3.TreatmentsExperiment was designed as randomized complete block (3)with four treatments,eachreplicated three times.Treatments were a monoculture of white cabbage,a monoculture ofChinese cabbage and a mixed crop of the two host plants species (random distribution ofseedlings).Mixed crop were included in two different treatments,where both brassicasS.Trdan et al./Scientia Horticulturae 106(2005)12–2414S.Trdan et al./Scientia Horticulturae106(2005)12–2415 were planted identically,but each designated for separate crop to analyze.Forty seedlings of white cabbage(variety‘Ditmar’),40seedlings of Chinese cabbage(variety‘Nagaoka’) and20seedlings from both brassicas(mixed crops in two separate treatments)were transplanted for each repetition.The spacing was30cmÂ45cm.The plot size (experimental unit)was4.0mÂ1.3m,having four rows,each with10plants.Adjacent plots were separated with non-planted buffer area(1.0mÂ1.3m)with an aim to diminish the impact of plants in neighboring plots.Only15randomly selected plants near the center of each plot were sampled to eliminate confounding effect of adjacent plots as much as possible.The extent of damaged leaf area caused byflea beetles was assessed four times in 2002and three times in2003.Additionally,flea beetles were counted ones in2002and twice in2003(Table1).2.4.Field observationsEPPO directive(OEPP/EPPO,2002)was used for evaluation of the extent(percentage) of damaged leaf area.In the natural infestation trial the leaves were qualitatively assessed on a scale from1(no damage)up to5(more than25%leaf area eaten).The intermediate values in the scale expressed the damage as follows:2—up to2%leaf area eaten, 3—between3and10%leaf area eaten,and4—between11and25%leaf area eaten.The growth stages of the plants were established using the BBCH scale for leaf vegetables (forming heads)(BBA,2001).The scale includes the principal growth stages as follows: 0—germination,1—leaf development(main shot),2—development of harvestable vegetative plant parts,5—inflorescence emergence,6—flowering,development of fruit, 8—ripening of fruit and seed,and9—senescence.To minimize the migration of beetles between plants,all evaluations were carried out in the morning,at about8a.m.with air temperature under158C.Beetles were counted only on the upper side of the leaf,as it is known thatflea beetles mostly feed on this side(Vargas and Kershaw,1979).Moving the leaves or using some instruments(i.e.vacuum aspirator) would disturb theflea beetles that would consequently aband the plants.As a result,the data would be less accurate than in the case of our method.Insects were only counted as long as leaves did not overlap(PGS118).2.5.Data analysisAn analysis of variance(ANOV A)was employed to assess the differences in the number offlea beetles per plant,and in the percentage of damaged leaf area among the treatments. Before analysis,each variable was tested for homogeneity of treatment variances.If variances were not homogeneous,data were transformed to log(Y)before ANOV A. Student–Newman–Keuls multiple range test(*P0.05)was used to separate mean differences among parameters in all treatments.The relationship between mean damage value,caused by feeding,and mean number offlea beetles was evaluated using linear and polynomial regression analysis.All statistical analyses were performed with Statgraphics Plus for Windows4.0(Statistical Graphics Corp.,Manugistics,Inc.)andfigures were created with Sigmaplot2002for Windows8.0(Systat Software,Inc.).Data are presented as untransformated meanÆS.E.S.Trdan et al./Scientia Horticulturae 106(2005)12–2416Table 1Dates of flea beetles,Phyllotreta spp.,countings and damage evaluations on leaves of white cabbage (C)and Chinese cabbage (CC)in 2002and 2003Year 20022003No.of flea beetles Damaged leaf area (%)Growth stage (BBCH)No.of flea beetles Damaged leaf area (%)Growth stage (BBCH)C CC C CCFirst evaluation 14August 14August a PGS 1:16–19PGS 1:18–1918September 18September PGS 1:14PGS 1:16Second evaluation –22August PGS 1:17–19PGS 1:1930September 30September PGS 1:17PGS 1:17–18Third evaluation –3September b PGS 4:41–42PGS 4:41–17October PGS 1:18–19PGS 1:19Fourth evaluation –20September PGS 4:44–47PGS 4:43–47––––a Principal growth stage 1:leaf development (main shot);10—cotyledons completely unfolded,growing point or true leaf initial visible;19—nine or more true leaves unfolded.b Principal growth stage 4:development of harvestable vegetative plant parts;41—heads begin to form,the two youngest leaves do not unfold;49—typical size,form and firmness of heads reached.S.Trdan et al./Scientia Horticulturae106(2005)12–2417 3.ResultsFor some of the treatments in both years,statistically significant differences were found in the extent of damaged leaf area,caused by feeding offlea beetles,Phyllotreta spp.,on leaves of white cabbage and Chinese cabbage grown in monoculture and in mixed crop. Differences were also found in some treatments in the occurrence offlea beetles on both brassicas.In thefirst evaluation in2002(P<0.001),the most extended injuries were observed on leaves of Chinese cabbage(from8up to11true leaves unfolded)grown in monoculture (4.6Æ0.10),and in mixed crop with white cabbage(4.5Æ0.14).No statistically significant differences were observed between these two treatments.In addition,no statistically significant differences were found between the mean damage values for the leaves of white cabbage(from6up to10true leaves unfolded)in monoculture(2.6Æ0.14) and in mixed crop(2.7Æ0.24).On the other hand,mean damage values for white cabbage were significantly lower than for Chinese cabbage for both treatments.The results were slightly different in the second evaluation in2002(P<0.001).The same mean damage values were determined for Chinese cabbage(from10up to17true leaves unfolded)grown in monoculture and in mixed crop(5.0Æ0.00).Therefore,no statistically significant differences were found between these two treatments.On the contrary,to thefirst evaluation,there were significant differences in mean damage values for white cabbage(from7up to10true leaves unfolded)for different treatments.The value was higher(4.7Æ0.08)when white cabbage was grown in monoculture than when grown in mixed crop(4.3Æ0.24).Statistically significant differences between some of the treatments were also found in the third evaluation(P<0.001),when both brassicas were in the stage BBCH41–42 (beginning to form heads).Mean damage values for the white cabbage grown in monoculture were significantly higher(3.7Æ0.14)than for the white cabbage grown in mixed crop(3.0Æ0.25),but for both treatments lower than in second evaluation.Mean damage values for Chinese cabbage were comparable for both treatments(5.0Æ0.00)and significantly higher than for white cabbage.In thefinal(fourth)evaluation in2002 (P<0.001),when brassicas were in the stage BBCH43–44(30–70%of the expected head size reached),mean damage values on the leaves of both brassicas were the lowest compared with other three evaluations.The highest mean damage values(3.1Æ0.09)were observed for Chinese cabbage grown in monoculture and in mixed crop with white cabbage (3.0Æ0.16).The extent of damages on white cabbage was on average1grade lower (2.2Æ0.08in monoculture,and2.1Æ0.17in mixed crop).Generally,injuries on the leaves of both brassica plants were on average assessed with higher grades in earlier developmental stages(Fig.1).Significant differences were observed in the mean number offlea beetles,Phyllotreta spp.,on white cabbage and Chinese cabbage in2002(P<0.001),irrespective of treatment.The number of beetles on Chinese cabbage grown in monoculture(12.3Æ1.21) and in mixed crop(11.1Æ1.21)was significantly higher in comparison to the number of beetles on white cabbage in monoculture(3.4Æ0.70)and in mixed crop(4.2Æ0.54 beetles per plant).The number was not significantly different on the level of the same host species but different treatment(CC versus CC-mixed,C versus C-mixed)(Fig.2).Betweenthe mean damage value (y )and mean number of flea beetles (x )in the time of first evaluation in 2002,statistically signi ficant and positive correlation was ing a polynomial regression analysis,a third order polynomial model,explaining 44%of the variability in mean damage value,was determined as optimal (y =2.15+0.36x À0.02x 2+0.0002x 3,R 2=43.7%,P <0.001).Less variability was explained by the model when using simple regression approach (y =2.86+0.10x ,R 2=30.0%,P <0.001).No signi ficant differences in the mean damage values and also in the number of beetles on the leaves for the same host species in different treatments were found in 2003in all three evaluations.The signi ficant difference between mean damage values in Chinese cabbage (3.9Æ0.14in monoculture and 3.8Æ0.26in mixed crop)and white cabbage (1.2Æ0.06in monoculture and 1.3Æ0.10in mixed crop)was observed.First evaluation in 2003(P <0.001)was performed at the same time as fourth evaluation in 2002,and corresponds to the first evaluation in 2002with regards to developmental stages of both brassicas.These are probably related to the lack of food for flea beetles (smaller leaves in earlier developmental stages of plants,less alternative food)and consequentially to less numerous population in 2003.S.Trdan et al./Scientia Horticulturae 106(2005)12–2418Fig.1.Mean damage values (ÆS.E.)on the leaves of white cabbage and Chinese cabbage,caused by feeding of flea beetles,Phyllotreta spp.,in four different treatments (n =15)in 2002.For each sampling period,data were analyzed by one-way ANOV A followed by Student –Newman –Keuls multiple range test (*P 0.05)for separation of means.The same letters are not signi ficantly different,and vertical lines represent standard errors of means.Abbreviations in the figure mean as follows:CC —Chinese cabbage,CC-mixed —Chinese cabbage in mixed crop,C —white cabbage and C-mixed —white cabbage in mixed crop.A reduced extent of damages was observed in the second evaluation (P <0.001)in comparison to the first evaluation in Chinese cabbage,presumably due to an enlargement of leaf surface and additional reduction of flea beetle population.The mean damage value in Chinese cabbage in monoculture was 3.4Æ0.08and in mixed crop with white cabbage3.2Æ0.12.The value of the same parameter in white cabbage in monoculture was1.2Æ0.08and a little higher in mixed crop 1.4Æ0.10.At the time of the third evaluation (P <0.001),which coincided with a gradual transition of flea beetles in diapause (overwintering),damage extent on the leaves was slightly reduced,due to the lower temperatures and thus slower plant development (Fig.3).There was no statistically signi ficant difference in the mean number of beetles per plant between the treatments with the same Brassica species in both evaluations.On the contrary,there was signi ficant differences in the number of beetles on different hosts.Thus,in the first evaluation (P =0.04),the mean number of beetles on Chinese cabbage grown in monoculture and in mixed crop was 5.3(Æ0.51and Æ0.67,respectively),and only a few beetles were found on white cabbage.Similar results were found in the second evaluation (P <0.001),only the mean number of beetles on Chinese cabbage was for about one specimen lower as compared to the previous evaluation (Fig.4).In the first evaluation in S.Trdan et al./Scientia Horticulturae 106(2005)12–2419Fig.2.Mean number of flea beetles,Phyllotreta spp.(ÆS.E.),on the leaves of white cabbage and Chinese cabbage,in four different treatments (n =15).Results are obtained at the time of the first evaluation (14August 2002).For each sampling period,data were analyzed by one-way ANOV A followed by Student –Newman –Keuls multiple range test (*P 0.05)for separation of means.The same letters are not signi ficantly different,and vertical lines represent standard errors of the means.Abbreviations in the figure have the same meaning as in Fig.1.2003,a signi ficant and positive correlation was observed between the mean damage value (y )and mean number of flea beetles (x ).Using polynomial regression analysis,a third order polynomial model,which explains 67%of the variability in mean damage value,was determined (y =1.35+1.15x À0.15x 2+0.01x 3,R 2=66.8%,P <0.001).Less variability was explained when using a simple linear regression model (y =1.72+0.30x ,R 2=47.0%,P <0.001).Similar models were estimated for the data from the second evaluation in 2003.Better performance was obtained again by the third order polynomial model (y =1.55+0.82x À0.10x 2+0.003x 3,R 2=53.3%,P <0.001)than by simple linear regression model (y =1.72+0.30x ,R 2=47%,P <0.001).4.DiscussionDuring the years 2002and 2003,weather conditions were very different (rainfall above the average in the first year and water shortage in the second year),but preference of flea beetles,Phyllotreta spp.,to both Brassica species was similar.In both years the number of beetles on Chinese cabbage,grown in monoculture or in mixed crop with white cabbage,was substantially higher than on white cabbage,grownS.Trdan et al./Scientia Horticulturae 106(2005)12–2420Fig.3.Mean damage values (ÆS.E.)on the leaves of white cabbage and Chinese cabbage,caused by feeding of flea beetles,Phyllotreta spp.,in four different treatments (n =15)in 2003.For each sampling period,data were analyzed by one-way ANOV A followed by Student –Newman –Keuls multiple range test (*P 0.05)for separation of means.The same letters are not signi ficantly different,and vertical lines represent standard errors of means.Abbreviations in the figure have the same meaning as in Fig.1.both ways.In 2002,the number of beetles in treatments CC and C was at ratio 3.67:1,and in treatments CC-mixed and C-mixed at ratio 2.63:1.Considering trap cropping,the ratio C:C-mixed 0.81:1is the most relevant data (2002).This means that white cabbage in mixed crop with Chinese cabbage is more exposed to flea beetle attack than if grown in monoculture.The reason is that the number of beetles on Chinese cabbage is so high –for the reason of intraspeci fic competition (Quiring and Timmins,1990;Lucas et al.,1995)–that they migrate to neighboring plants,in this case to white cabbage.In 2003damage evaluation started approximately 1month later (beginning of September,due to very high temperatures which enabled the seedlings to survive in August)than in 2002.The ratio between number of beetles on both brassicas in 2003,grown in the same way (CC:C and CC -mixed:C-mixed)was over 10times higher.Differences in susceptibility of the pest to both brassicas in both years are mostly of abiotic nature,because moderate temperatures at the beginning of the experiment in 2002were more favorable for the pest and its hosts,as it is known for many phytophagous insects and plants they attack (Raj et al.,1995;Tang et al.,1999).The main reason for substantially greater values of CC:C and CC-mixed:C-mixed in 2003than in 2002is in the lower number of beetles on white cabbage in the second year.S.Trdan et al./Scientia Horticulturae 106(2005)12–2421Fig.4.Mean number of flea beetles,Phyllotreta spp.(ÆS.E.),on the leaves of white cabbage and Chinese cabbage,in four different treatments (n =15).Results are obtained at the time of the first and second evaluation (18September and 30September 2003).For each sampling period,data were analyzed by one-way ANOV A followed by Student –Newman –Keuls multiple range test (*P 0.05)for separation of means.The same letters are not signi ficantly different,and vertical lines represent standard errors of the means.Abbreviations in the figure have the same meaning as in Fig.1.The number of beetles on white cabbage at the time of first evaluation (when developmental stages of both brassicas were comparable)was more than 26-times lower (C-mixed 2002:C-mixed 2003=26.44:1).The exact ratio of number of beetles in monoculture was not determined,since in first evaluation in 2003not even a single beetle was found.Ratio between C and C-mixed (0.00beetles per plant/0.16beetles per plant)in first evaluation in 2003is less relevant than the same ratio in second evaluation (0.42:1)in the same year.Due to more favorable weather conditions in 2002,the ratio C:C-mixed for this year was considered as more relevant.Results have thus con firmed previously known statements of higher preference of flea beetles to Chinese cabbage,in comparison to white cabbage (Kinoshita et al.,1979).In 2002,which was more favorable for growing both brassicas,mean extent of damage leaf area on Chinese cabbage in both treatments was very high (mean damage value about4.5)already in the first evaluation.At the time of the second evaluation,all plants of Chinese cabbage were assessed with the highest number on the scale.The situation was the same in the third evaluation,while in the fourth evaluation about 10%of leaf area was damaged on Chinese cabbage.This is probably the result of quick growth of leaf surface,and natural decrease of population of the pest,bearing in mind that feeding of flea beetles on damaged plants increases its natural mortality (Traw and Dawson,2002).Mean damage value on white cabbage,grown in monoculture or in mixed crop with Chinese cabbage were substantially lower as compared with Chinese cabbage.Leaves of white cabbage were most damaged at the time of the second evaluation,when the mean damage value was more than 4.The population of flea beetles in 2003was substantially lower than in 2002and so was the damage on the leaves of both brassicas.The extent of damage on leaves of Chinese cabbage was the highest in first evaluation in both treatment.The same parameter on leaves of white cabbage was surprisingly the highest in the second evaluation.We assume that this is due to a slower growth of white cabbage and so the leaves in second evaluation were already previously assessed.On the other hand,Chinese cabbage grew more rapidly,thus compensated damage observed in first evaluation.As the damage on leaves of both brassicas is not in fluenced only by the number of flea beetles,but also by several biotic and abiotic factors,the direct impact of the number of flea beetles on the damage was investigated.Polynomial regression was found as an appropriate method for describing such relationship.Third order polynomial model explained 44–67%of variability in damage as a function of the number of flea beetles.In more favorable years for brassicas growing (in our case 2002),other factors beside the number of beetles intensity the damage,caused primarily by the flea beetles feeding on leaves.Favorable conditions for brassicas growing are also favorable for flea beetles,which migrate more intensively between plants and between parcels.Less variability explained by the polynomial model in the second evaluation in year 2003(R 2=0.53versus 67%)can also be explained as the holes on leaves were a result of flea beetles feeding during both –first and the second –evaluations.According to the results derived from the 2-year experiment we concluded,that Chinese cabbage growing as a trap plant for flea beetles in mixed crop with white cabbage,is not a suf ficient control measure,because no statistically signi ficant differences were found between the number of beetles on white cabbage,grown in monoculture and in mixed culture in a majority of evaluations.Obviously,Chinese cabbage is a very susceptible hostS.Trdan et al./Scientia Horticulturae 106(2005)12–2422S.Trdan et al./Scientia Horticulturae106(2005)12–2423forflea beetles,so the mass occurrence of beetles on this vegetable also causes higher migration of beetles to white cabbage,thus causing a quite important extent of damage also on white cabbage.On the other hand,no statistically significant differences were observed in the number of beetles as well as in the damage extent on leaves of Chinese cabbage grown in two different ways.Values of both parameters were in all evaluations statistically and significantly higher from adequate values on white cabbage.We suggest that selective chemical control offlea beetles on Chinese cabbage plants,grown in mixed crops where white cabbage is the main crop,could diminish harmfulness offlea beetles,which will be in Europe probably also in the future one of the most important pest of brassicas in early developmental stages.In the area where this research was performed,early cabbage varieties are harvested between the end of June and beginning of July,so spraying Chinese cabbage with insecticides is recommended only in production of late white cabbage. 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