Optimizing insect pest control and nitrogen fertilizing of the summer turnip rape (Brassica campestris sutiva) Sirpa Kurppa and Antti Ollula KURPPA, S.& OLLULA, A. 1993. Optimizing insectpest controland nitrogenfertilizing ofthe summer turnip rape (Brassica campestris sotiva). Agric. Sci. Finl. 2:149-160. (Agric. Res. Centre ofFinland, Inst. Plant Protect., FIN-31600 Jokioinen,Finland.) The need for pest control could not be decisively reduced by boosting the compensatory ability of the summer turnip rape with extra nitrogen fertilizer. The plant compensated the damage of the blossom beetle (Meligethes aenus F.) by producing additional axillary racemes, pods and seeds. The compensation, in plant stands with about 300 plants/m2, reached its maximum capacity with a nitrogen quantity of 90 - 110 kg/hectare and covered about 30% of the harvest loss inflicted by the large blossom beetle population. Only, when the blossom beetle population barely exceeded the control threshold (one beetle per plant at the early bud stage) harvest loss was fully compensated by the extra nitrogen. The damage inflicted by the flea beedes (Phyllolrela spp.) was better compen- sated, however, the importance of the preventive seed treatment became evident during dry and especially warm emergence periods, when the threshold of 30 holes per plant was exceeded. The use of extra nitrogen, above the moderate 70 - 90 kg/ha, was found toyield 400 kg per hectare at the most, with insecticides the yield increased maximally by more than 1000 kg per hectare. The moderate quantity of nitrogen was, also, sufficient to produce the best operating margin in the cultivation even in heavy mineral soils. Key words: summer turnip rape, Meligethes aeneus, rape blossom beetle, flea beetle, Phyllotreta spp., nitrogen, pyrethrin, permethrin, compensation, operating margin Introduction The adaptability of cruciferous oilseed plants to varying growing conditions is generally good, and nitrogen in particular plays a key role in the com- pensation ability (Tatchell 1983, AUGUSTINUS- sen 1987, Lamb 1989, Axelsen and Nielsen 1990). Determining the right proportions of nitro- gen fertilization and fungicide treatments has been found to ensure steady yields and to be the essential factor in achieving a good economic result (Hanus and SCHOOP 1989). In Sweden, Wallgren and Radberg (1989) obtained the best economic re- suits with a nitrogen fertilizationrate of 90 kg/ha in their own experiments. In Finland, a nitrogen fer- tilization rate as high as 150 kg/ha has been found to increase the yield of summer turnip rape. In the same experiment, application of the nitrogen fertil- izer at two stages, i.e. two thirds at sowing and one third at the seedling stage, failed to increase the yield (Köylijärvi and Pahkala 1989). The economic implications of using additional nitrogen were not compared in the experiment. The species causing the most plant protection problems in the Finnish summer rape cultivation areas is the blossom beetle (Meligethes aeneus F.), 149 Agric. Sei. Finl. 2 (1993) https://www.c-info.fi/en/info/?token=p1qwbUye0mo33nNm._XyG6Bm592cKGMMu7a8kNA.nmzlgqyFqGsTwN-HzkL3uv89iLEKTX-FB1UOH5k7aHslrmp-HKgZXhAiElA2-YaZym695bp__qeGZzfdF86A55TkqREcJ73JOlMSWCgqiIcJ5iRCuC0Y5qsAGBMjnJprFOvxVLr4R1D4uu62b-kejRBarcXj3cybicP-zn1v5ncVwwk603YZWYurN4A--4p7k8aMb5FobM94illuY_DfgSQuYs6Koe4zpb8RcYvkwbA7FXBgghOJ_cM7z8yMQcMQxEMoqu8NZBSNeIkcGbNOdu1cyO8 Table 1, Soil type, acidity and nutrient content in the experimental fields in 1991—92. Experimental site Year Soil type pH Milligrams/litre Ca P K Jokioinen 1991 Sandy clay 6.0 2353 11.1 224 1992 Sandy clay 6.2 2473 13.6 178 Lepaa 1991 Gytja clay 6.320.5 230 1992 Gytja clay 6.319.3 219 Mouhijärvi 1991 Silty clay 6.0 1230 8.1 128 Pälkäne 1991 Finer fine sand 5.5 1089 7.1 133 Ylistaro 1991 Mould 5.4 2148 5.7 118 although the crop losses ascribed to it have gener- ally not exceeded 10% in fields sown with summer turnip rape (Tulisalo and WuORl 1986). The pest control threshold for the blossom beetle is one beetle per plant at the early bud stage of the summer turnip rape, and 2 to 3 beetles per plant before blossoming, if the aim is to manage with one con- trol spraying only. According to Hokkanen et al. (1986), only the outer edges of the fields shouldbe treated when the control thresholdfor the blossom beetle is lower. This study of cultivation techniques aimed at identifying those agricultural and economic aspects that should be taken into account in extending the cultivation of turnip rape and rape to non-food ag- ricultural use, optimizing production input, and creating ecologically more acceptable production methods. Production of rapeseed oil esters would be an alternative, if economic and ecological ac- ceptability criteria could be met. Material and methods In 1991, field trials were carried out at five sites: in Jokioinen (600 80’ N, 230 50’ E), Lepaa (610 11’ N, 240 37’ E), Mouhijärvi (610 51’ N, 230 01 ’ E), Pälkäne (610 32’ N. 240 28’ E) and Ylistaro (620 93’ N, 220 43’ E), and in 1992 on two sites, i.e. Jokioinen and Lepaa. The soil types and fertility rates of the trial sites are shown in Table 1. As for the important phosphorous content (Saarela and Köylijärvi 1989), the scale of adequate (Pälkäne, Ylistaro), fair (Jokioinen 1991, Mouhijärvi) and good (Jokioinen 1992 and Lepaa) was represented. The experimental design followed the strip-plot arrangement, with randomized fertilizer and com- bined herbicide, fungicide, insecticide and growth regulator treatments. Trial plots, measuring 4 by 10 metres, were in replications of four. The experi- mental results were analyzed using MSTAT and SAS statistical software, especially using two-way analysis of variance. Significance levels are indic- ated in the tables with asterisks placed on the right hand side of the corresponding F-value as follows: *** p = 0.001, ** P = 0.01 and * P = 0.05. The fertilizer levels, herbicide, fungicide, insect- icide and growth regulator treatments used in field trials are shown below. Year 1991: al 70kgN/ha a 2 90 kg N/ha a 3 110kg N/ha *a4 70 + 20 kg N/ha at seedling emergence b 1 no seed dressing or other treatments b 2 no seed dressing, rape blossom beetle control- led by pyrethrin b 3 herbicide, dressed seed, rape blossom beetle controlled by permethrin, plant growth regu- lator *b4 herbicide, dressed seed, rape blossom beetle controlled by permethrin, plant growth regu- lator, couch grass control * at Jokioinen only Year 1992: al 70 kg N/ha a 2 110kg N/ha a 3 70 +4O kg N/ha at seedling emergence 150 Agric. Sei. Fint. 2 (1993) Table 2. Dates of sowing, plant protection and fertilizer treatments, and harvest in 1991—92. Jokioinen Lepaa Mouhijärvi Pälkäne Ylistaro Year Treatment 1991 1992 1991 1992 1991 1991 1991 Sowing 17.5. 15.5. 15.5. 20.5. 23.5. 22.5. 27.5. Insecticide 1 26.6. 9.6. 27.6. 17.6. 25.6. 28.6. 1.7. Insecticide 2* 8.7. 15.6. ... . 8.7. Foliage fertilizer - 15.6. - 17.7. ... Couch grass control" 27.6. 15.6. - 17.6. - 25.6. Growth regulator 1.7. 25.6. 27.6. 29.6. 25.6. 28.6. 8.7. Additional N 24.6. 16.6. - 17.6. Fungicide - 3.7. - 9.7. ... Harvest 13.9. 10.9. 9.9. 11.9. 18.9. 24.9. 18.9. * In Jokioinen extra insecticide sprayed 1.7.1991 ” In Pälkäne fluazephop butyl sprayed on the whole field. Additional N = additional N at seedling emergence bl no seed dressing or other treatments b 2 no seed dressing, rape blossom beetle control- led by pyrethrin b 3 herbicide, dressed seed, rape blossom beetle controlled by permethrin b 4 herbicide, dressed seed, rape blossom beetle controlledby permethrin, couch grass control, foliage fertilizer, growth regulator, fungicide The cultivation techniques followed normal practices as closely as possible. The growth stages of rape were graded by theBBHC-Decimal-Codes (Weber and Bleiholder 1990). The sowing dens- ity was 375 germinating seeds per square metre, the cultivars were ’KOVA’ in 1991 and ’KULTA’ in 1992. Seed was dressed by Oftanol T (isofenphos 400 g/kg, thiram 100g/kg) 20 g/kg seeds. For basic fertilization, high nitrogen ’Typpirikas y-lannos 2’ (N-P-K 20-4-8) was spread as band placement. Before tilling, treatments b 3 and b4, which con- sisted of the herbicide ’Super Treflan’ containing trifluralin (480 g/1), in 1991 2.5 1/ha and in 1992 2 1/ha, were carried out. Natural pyrethrin in the form of ’Bioruiskute S’ (100 g active ingredient/1), in 1991 0.5 1/ha and in 1992 0.6 1/ha, and the per- methrin preparation ’Ambush’ (250 g active ingre- dient/1), in 1991 0.4 1/ha and in 19920.5 1/ha, were used as insecticides against the blossom beetle. For additional nitrogen (in 1991 20 kg/ha, in 1992 40 kg/ha) potassium nitrate ’Peltokalkkisalpietari’ (N-P-K 15.5-0-0, Ca 19%, Mg 0.2%) was top dressed. Foliage fertilizer ’Rypsin lehtilannos 2’ (N 3%, Mg 6%, Mn 5%, B 3%, Mo 0.5%, S 11.2%) was used at the rate of4 kg/ha. ’Cerone’ (0.5 1/ha), containing etefone (480 g/1), was used as a growth control spray and ’Fusilade 2000’, containing fluazephop butyl (125 g/1, 3 1/ha), was used as herbicide for couch grass. The prochloraz ’Sportak 45 EC’ (450 g/1, 1 1/ha), was used to control Sclerotinia rot. Water was used at the rate of 300 litres per hectare in the trials. The control threshold of the blossom beetle was one beetle per plant at budding stage (BBFIC 51 - 52), and two to three beetles per plant before blos- soming (BBHC 53 - 54). Herbicide was sprayed on couch grass at the four or five leaf stage. Plant growth regulator was sprayed while the stems were gaining height but before blossoming (BBHC 53 - 54 ). Sclerotinia rot was controlled by spraying when the first petals were being shed (BBHC 63). In Jokioinen in the spring of 1992, seedlings in the plots sown with untreated seed were severely dam- aged by flea beetles (Phyllotreta spp.), necessitat- ing an insecticide spray application of the experi- mental field, without whichall the seedlings would have been consumed by the flea beetles. Permethrin (’Ambush’ 0.5 1/ha) mixed with 300 litres of water per hectare was used as insecticide. The cultivation measures per trial site are shown in Table 2. 151 Agrlc. Sei. Fin I. 2 (1993) The experimental plots were investigated under the vegetative period as described in Table 3. The method of Nielsen and Axelsen (1988) was used in screening the rape blossom beetle. Experimental conditions The experimental years were very different in terms of climatic conditions. In 1991, the beginning of May was cool and rainy. In Jokioinen, for instance, the cumulative degree-days of the growing season fell about 90°C short of the long-termaverage tem- perature by mid-June. In early August the weather turned warm, which accelerated the growth and ripening of the plants. In 1992, May was warm and devoid of rainfall. In June and July the weather was warmer than normal. By mid-June the cumulative degree-days of thegrowing season exceeded the long-term aver- age temperature by about 145°C in Jokioinen. The first rains that the plants could benefit from fell in mid-June. The following figure (Figure 1) and table Table 3. Monthly precipitation (mm) for each experimental site in 1991—92. Experimental Year May June July Aug Sep site Jokioinen 1991 29 69 55 92 80 Jokioinen 1992 7 25 47 153 19 Lepää 1991 27 70 20 66 611991 27 70 20 66 61 Lepää 1992 12 36 64 92 97 Mouhijärvi 1991 32 69 29 71 92 Pälkäne 1991 22 88 41 193 681991 22 88 41 193 68 Ylistaro 1991 56 147 26 60 88 Table 4. Influence of seed dressing on the damage of flea beetles (Phyllotreta spp.), holes/plant in summer turnip rape at each trial site. Experimental Jokioinen Mouhijärvi Pälkäne site Year 1991 1992 1991 1991 Treatment No dressing 5.5 a 35.4 a 5.6 a 4.9 a Seed dressed 3.4 b 8.7 b 2.5 b 3.6 b F-value 42.7*" 1002.6*** 51.1*** 4.3* 152 (Table 3) show the cumulative degree-days of the growing season (°C) and monthly precipitation (mm) for each experimental site in 1991 and 1992. Results The weeds occurred only occasionally at all experi- mental sites and no yield loss could be attributed to the weeds. Efficacy of insect control In nearly all experiments seed dressing had a sig- nificant (P<0.01) effect on the damage inflicted by flea beetles on summer turnip rape (Table 4). In terms of yield, the damage observed during 1991 was insignificant. The damage inflictedby the flea beetle did not exceed the minimum damage density found to reduce the yield in the actual seed dressing trials, i.e. 30 holes per plant (cf. Kurppa 1991).The draught early in the summer of 1992 clearly ham- pered the emergence of summer turnip rape seed- lings. The cotyledon stage of the seedlings lasted unusually long (over a month), which created con- ditions favourable for seedling damage to occur. The flea beetles would, in fact, have "cleaned out" the untreated plots if the seedlings had not been sprayed. The size of the blossom beetle populations varied greatly between trial sites. Highly significant (P<0.01) reductions in population size were achieved through various insect control measures at almost all trial sites (Table 5). In plant stands treated with natural pyrethrin, the number of blos- som beetles per plant was reduced by spraying, only to be restored within 48 hours to almost the same level as before the treatment. Permethrin treatments proved to be far more long acting at all trial sites, being effective for one week on average. Vegetational stem growth Stepwise increased nitrogen fertilisation boosted stem growth significantly (P<0.05) at two trial sites Agric. Sd. Finl. 2 (1993) Table 5. Influence of insecticide spray on the number of rape blossom beetles (Meligethes aeneus) per plant in summer turnip rape at each trial site. Experimental site Jokioinen Lepaa Mouhijärvi Pälkäne Year Treatment 1991 1992 1991 1991 1991 Untreated 3.4 a 20.8 a 0.5 a 1.7 a 2.6 a Pyrethrin 1.2 b 7.6 b 0.3 a 1.3 a 2.0 a Permethrin 1.6 b 3.1 c o.lb 1.0 b 1.3 b F-value 3.9' 90.1"* 5.9" 5.9" 13.9"* (Pälkäne and Ylistaro) (Table 6). Ylistaro was the northernmost trial site with highest precipitation and situated on organic soil; Pälkäne had a fairly poor nutritional level in the soil, next highest June precipitation and low final yield (Table 1,3, 10). Etefone treatment reduced stem growth in the summer turnip rape significantly (P<0.05) in dry and nutritionally best trial sites (Jokioinen and Lepaa). This treatment, however, failed to show a significant effect on stem growth at the north- ernmost trial site (Ylistaro), where the vegetation grew highest. Insecticide and plant growth regu- lator sprayed in close succession (2-3 days be- tween treatments), in 1991,resulted in a substantial reduction in stem growth, averaging 20 cm com- pared to the untreated plant stand. This was ob- served in nutritionally high standard clay soil in Jokioinen, where the period immediately before and after the application was dry. The same treat- ment combination had not the same effect at other trial sites that were situated in finer sand, included lower quantities of calcium, phosphorous and potassium, and received arain shower of7.8 mm on the day of application. Vegetational branching In general terms the branching of summer turnip rape became poorer with increasing growth density. In 1991, the growing conditions were excellent at the trial site in Lepaa, where even minor measures designed to boost growth, e.g. increasing the quant- ity of nitrogen fertilizer, in addition to more effect- Fig. 1.The cumulative effective degree-days of the growing season for each trial site in 1991 - 92. Maximum values in 1991: Jokioinen (JOK) 1112°C, Lepaa (LEP) 1181°C,Pälkäne (PLK) 1195°C, Mouhijärvi (MOUH) 1087°C and Ylistaro 1057°C, in 1992: Jokioinen 1223°C,Lepaa 1291°C. 153 Agric. Sei. Fin!. 2 (1993) Table 6. Influence of the rate of nitrogen fertilization and pesticide treatments on the stem growth of summer turnip rape at each trial site. Experimental site Jokioinen Lepaa Mouhijärvi Pälkäne Ylistaro Year Treatment 1991 1992 1991 1992 1991 1991 1991 N 70 69 81 10(1 67 - 78 b 101 b N 90 74 91, 75 87 a 107 ab N 110 74 85 99 69 72 88 a 105 ab N 70 + 4 1 71 86-67 - - - LSD (0.05) ns ns ns ns ns 6.58.7 Untreated 77 a 84 b 103 a 67 b 72 85 111 Pyrethrin 78 a 86 ab 102 a 68 b 79 87 111 Permethrin 2 75 a 91a 90 b 73 a 71 81 101 P+ C + F + S+ FF 3 58 b 77 c 62 c LSD (0.05) 4.75.5 10.43.2 ns ns ns 1 Jokioinen 1991 N 70 + 20 2 in 1991 with etefone 3 P+C+F+S+FF = permethrin, etefone, fluazephop butyl, prochloraz, foliage fertilizer exception: in 1991 Jokioinen prochloraz and foliage fertilizer missing ive insecticide treatments, were observed to in- crease branching slightly despite the high growth density (304 plants/m2) (Table 7). In 1991,also the interaction of fertilizer and plant protection treat- ment was significant at the trial site in Jokioinen, where the plant stand (a4bl) given the most fertil- izer and left without any treatments branched sig- Table 7. Influence of the rate of nitrogen fertilization and pesticide treatments on the number of racemes/plant of sum- mer turnip rape at each trial site. Experimental site Jokioinen Lepaa Mouhi- järvi 1991 1992 1991 1991Year Treatment N 70 4.2 7.5 3.5 b 7.0 N 90 4.9 - 3.9 a 5.5 N 110 4.9 7.7 4.2 a 5.8 N 70 + 40' 5.2 7.4 F-value 2.3 ns 0.2 ns 3.3* 2.6 ns Untreated 4.9 8.8 a 3.8 b 7.2 a Pyrethrin 5.3 9.8 a 3.4 b 5.5 b Permethrin2 4,9 6.0 b 4.3 a 5.5 b P+C+ F+S + FF3 4.15.7 b F-value ns 18.6’” 5.2* 4.4* Interaction 2.3’ ns ns ns 1 Jokioinen 1991 N 70 + 20 2 in 1991 with etefone 3 P +C+F+S + FF = permethrin, etefone, fluazephopbu- tyl, prochloraz, foliage fertilizer exception: in 1991 Jokioinen prochloraz and foliage ferti- lizer missing nificantly more than any other plant stand, averag- ing 6.7 racemes per plant. Crop blossoming period Combination of the plant protection treatments had a very significant (P<0.01) effect on the length of the blossoming period of summer turnip rape, which for the untreated plant stand averaged 16 days, whereas that of the chemically treated plant stand was nearly 6 days longer. In the plant stand treated with natural pyrethrin, a slight increase (1 day) in the blossoming period was observed, com- pared with the untreated plant stand. The presence of a large number of blossom beetles and their larvae in the blossoms led to therapid withering of the blossoms in the plant stands treated with natural pyrethrin or left untreated. Number of pods and seeds Using more fertilizer boosted the number of pods per raceme at least up to the 90 kg/ha level, with the exception of the trial site in Mouhijärvi, where a strong contradictory trend was observed. There the interaction of fertilizer and control treatment was significant, the highest quantity of pods per raceme 154 Agric. Sd. Finl. 2(1993) being found in treatment (a 1b3) consisting of the smallest quantity of fertilizer and the best plant protection treatment. Permethrin treatment in- creased the quantity of pods per raceme most no- ticeably at the trial sites with the largest blossom beetle populations (Table 8). The use of fertilizer and the combination of plant protection treatments resulted in a significant dif- ference in the number of seeds per pod (Table 9). The interaction of fertilizer and plant protection treatments was highly significant in the 1991 trial in Jokioinen, where the highest average number of seeds per pod, 23.6, was observed with the treat- ment including the largest quantity of fertilizer and the most abundant plant protection treatments. Final yield In 1992, the effect ofplant protection treatments on yield was highly significant (P<0.01) at the trial sites with the best growing conditions, in Jokioinen and Lepaa (Table 10). In the present experiment pyrethrin treatment either failed to increase the tur- nip rape yield per hectare, or the increase was only slight (in Jokioinen 112 kg/ha, inLepaa 60 kg/ha in 1992), which in a way demonstrated that the prepa- ration was too short-acting for the blossom beetle. The best increases in yield were obtained with per- methrin treatments (up to 1000 kg) at the trial sites with the largest blossom beetle populations. Plant growth regulator used together with couch grass herbicide reduced the yield in Jokioinen. These results seem to indicate that caution should be exercised in using herbicides for couch grass together with plant growth regulators when grow- ing summer turnip rape, or that sufficiently long intervals between spray application should, at least, be allowed. The top yield was achieved in 1991 with treat- ments including fertilizer at the rate of 110 kg N/ha (1653 ± 102 kg/ha), and in 1992 the highest rate was achieved with treatments including 70 + 40 kg N/ha (2163 ± 69 kg/ha). And yet, increasing the quantity of nitrogen had a significant effect in only two cases out ofseven, ranging between 70 and 110 kg (Table 10). Table 8. Influence of the rate of nitrogen fertilization and pesticide treatments on the number ofpods/raceme of sum- mer turnip rape at each trial site. Jokioinen Lepaa Mouhi-Experimental site järvi Year 1991 1992 1991 1991 Treatment N 70 6.5 b 58.0 26.7 b 40.0 N 90 25.6 a - 31.5 b 36.3 N 110 22.1 a 63.1 44.2 a 35.122.1 a 63.1 44.2 a 35.1 N 70 + 40' 19.5 a 65.4 F-value 4.6*' ns 10.2*” ns Untreated 13.0 b 56.8 32.0 b 40.1 Pyrethrin 14.4 b 67.2 28.9 b 34.0 Permethrin2 30.4 a 63.7 39.2 a 36.7 P+C+F + S +FF 3 24.960.1 F-value 23.0’*' ns23.0’*' ns 3.7’ ns Interaction ns ns ns 2.62* 1 Jokioinen 1991 N 70 + 20 2 in 1991 with etefone 3 P +C +F+ S +FF = permethrin, etefone, fluazephopbu- tyl, prochloraz foliage fertilizer exception: in 1991 Jokioinen prochloraz and foliage ferti- lizer missine Table 9. Influence of the rate of nitrogen fertilization and pesticide treatments on the number ofseeds/pod of summer turnip rape at each trial site. Experimental site Jokioinen Mouhijärvi Treatment N 70 17.220.3ba N 90 19.1 ab 19.6 ab N 110 20.5 b 17.5 a N 70 + 20 20.1 b F-value 5.82"' 4.33* Untreated 18.7 a 19.7 b Pyrethrin 18.7 a 17.1 a Permethrin 1 20.8 b 20.5 c P + C +F 18.8 ab F-value 2.79* 6.36" Interaction 6.12"* ns 1 with etefone The increase in turnip rape yield, obtained with fertilizer and plant protection treatments, was at- tributable to different yield factors at various trial sites. The best initial growth was observed at a trial site with best nutritional conditions (phosphorous especially) in Lepaa, where the higher yield was 155 Agric. Sei. Finl. 2 (1993) Table 10. Influence of the rate of nitrogen fertilization and pesticide treatments on the yield (kg/ha) of summer turnip rape at each trial site. Experimental site Jokioinen Lepaa Mouhijärvi Pälkäne Ylistaro Year Treatment 1991 1992 1991 1992 1991 1991 1991 N 70 1051 2192 2851 b 1867 1001 709 b 1370 N 90 1402 - 3124 a 1102 1105 a 1439 N 110 1334 2333 3185 a 1884 1299 1064 a 1489 N 70 + 40 1 1310 2389 - 1935 LSD (0.05) ns ns 242 ns ns 160 ns Untreated 788 c 1959 c 2951 1603 b 1101 b 922 1420 Pyrethrin 877 c 2071 b 3048 a 1663 b 1030 b 912 1484 Permethrin 2 1835 a 2613 a 3161 2097 a 1271 a 1044 1394 P + C + F + S + FF 1597 b 2578 a - 2218 a LSD (0.05) 142 79 ns 140 108 ns ns 1 Jokioinen in 1991 N 70 + 20 2 in 1991 with etefone 3 P +C+F+ S +FF = permethrin, ’etefone’, fluazephop butyl, prochloraz, foliage fertilizer exception: in 1991 Jokioinen prochloraz and foliage fertilizer missing due to slight increases in branching and number of pods per raceme (Tables 7 and 8). In the plant stand in Mouhijärvi, with the poorest initial growth pat- tern, the increase in yield was due to slight in- creases in growth density and number of seeds pet pod (Table 9). In Jokioinen, which was a kind of average between the two sites mentionedabove, the higher yield was attributable to increases in the quantity of racemes and number of seeds per pod (Tables 7 and 9). Profitability ofcultivation In this experiment the profitability of cultivation was assessed in terms of the operating margin, in other words, by deducting from the gross profit the variable cost items, i.e. expenses directly attribut- able to the cultivation of the plant in question. The following list shows the unit prices on which the operating margin calculations were based, and the operating margin of summer turnip rape in Finnish marks (FIM/ha) per each treatment during 1991 and 1992 (prices are standard prices of 1991). Yield: summer turnip rape 4.053 FIM/kg (no mar- keting tax included) Variable production costs: - seed (not dressed) 15 FIM/kg - seed (dressed) 24 FIM/kg - preparatory work and drilling 250 FIM/ha -herbicide, ’Super Treflan’ (trifluralin) + treat- ment cost 284 FIM/1 - fertilizer, ’Typpirikas Y-lannos 2’ 1.94 FIM/kg - fertilizer for additional nitrogen, ’Peltokalkki- salpietari’ 1.61 FIM/kg -foliage fertilizer, ’Rypsin lehtilannos’, 17.50 FIM/kg -insecticide, ’Bioruiskute S’ (pyrethrin) 208 FIM/1 - insecticide, ’Ambush’ (permethrin) 402 FIM/1 -plant growth regulator, ’Cerone’ (etefone) 227 FIM/1 -fungicide ’Sportak 45 EC’ (prochloraz), 246 FIM/kg -herbicide for couch grass control, ’Fusilade 2000’ (fluazephop butyl), 284 FIM/1 -extra fertilizing or plant protection spray, la- bour and machinery, 65 FIM/ha/application - combine harvest 780 FIM/ha - drying 0.12 FIM/kg To obtain an economically acceptable result, it is necessary that the field to be sown is in a good 156 Agric. Sei. Finl. 2 (1993) condition and free of annual and perennial weeds, as herbicide treatments can easily become a notice- able cost factor in the cultivation of summer turnip rape. In most cases the treatment including the most fertilizer (110 kg N/ha) gave the best operating margin, although the difference was minor. In 1991, the differencebetween the nitrogen levels of 90 kg/ha and 110 kg/ha were not statistically sig- nificant at any trial site, and a difference in effect between nitrogen levels of 70 kg/ha and 90 kg/ha on various organic soils could not be demonstrated. On the basis of the above, the optimum quantity of nitrogen fertilizer was assessed to range between 70 and 90 kg/ha. When the control thresholdof theblossom beetle was barely exceeded, i.e. there was one beetle per plant at the early bud stage, natural pyrethrin treat- ment alone gave a satisfactory economic result (1991 trial in Lepaa, Fig. 2). When blossom beetles were more plentiful, a satisfactory or good economic result necessitated repeated treatments with synthetic pyrethroid (cf. 1992 trial in Jo- kioinen, Fig. 2). Discussion Current guidelines for cultivating turnip rape in- clude a recommendation for relatively high levels of nitrogen fertilizer, compared with the results obtained in summer rape trials in Denmark (cf. Augustinussen 1987). In the present study, how- ever, raising the nitrogen fertilizer level from 70 kg/ha to 110 kg/ha increased the yield in only one third of the trials, by about 400 kg/ha at the best, and the use of nitrogen failed to compensate ade- quately for the omission of insect pest control measures, the effect of whichpeaked 1000 kg/ha at its worst. In Finnish turnip rape plant stands of normal density (generally more than 200 plants per m2), compensation by cruciferous oilseed plants by means of branching cannot influence the result through prolific growth, unlike plant stands of about half the density (cf. Tatchell 1983, Augustinussen 1987, Nilsson 1988, Axelsen and Nielsen 1990). The utilizationof nitrogen dur- ing dry summers will in all likelihood be poor, and the additionalnitrogen will not boost compensation in the manner demonstrated elsewhere (cf. Dae- belerat al. 1980). In dry conditions, massive inva- sions by blossom beetles have been demonstrated to cause stunted growth on top of the shoots, as reported by NILSSON (1988). Due to the unpre- dictability of the growing conditions in Finland, fertilizer levels around 90 kg/ha would seem to effectively ensure a reasonable compensation ca- pacity in the summer turnip rape of a cultivar sim- ilar to ’Kulta’, even in heavy mineral soils. Under good growing conditions, and in organic soils, 70 kg/ha of fertilizer will suffice; in other words the minimum quantities of fertilizer recommended by Köylijärvi and Pahkala (1989), or even slightly less, would seem sufficient. In 1991, the damage observed in summer turnip rape seedlings, which was attributed to the flea beetle, was of hardly any consequence to the yield. The flea beetle population barely exceeded the con- trol threshold ofone flea beetle per plant suggested by Augustin et al. (1986). When the beetle popu- lation is large, however, and theemergence of seed- lings is slow due to a cold or dry early spring, seed dressing results in denser and more robust plant stands than would be the case with untreated seed. In a poor year, such as 1992, the plant stands sown with undressed seed might be totally destroyed in some areas. To avoid total destruction, insecticide spraying will be necessary at the seedling stage, like in the 1992 trials. The extent of the damage inflicted by the flea beetle depends largely on the weather, and in Finnish long-term experiments re- duced yields attributable to this cause have been found to occur every three years on average (Kurp- pa 1991). In the absence of resistance, one pest control measure applicable to the flea beetle would be seed dressing with pyrethrin, but its effective- ness in dry summers should be improved (Ketola 1992, pers. commun.). The control threshold of the blossom beetle of one insect per plant at an early bud stage was con- firmed as correct by the results of the present ex- periment. This control threshold is low compared to the conditions in Central Europe (cf. Seidel and 157 Agric. Sei. Finl. 2 (1993) Fig. 2. The operating margin in the production of summer turnip rape (FIM/ha) in 1991 and 1992 at each trial site. Above the columns significant differences (0.0.1) between the nitrogen treatments are indicated by capitals (A, B, C) and between pesticide treatments by small letters (a, b, c). 158 Agric. Sei. Fint. 2 (1993) Daebeler 1986, Vietinghoff and Daebeler 1986), but the difference is mainly due to varying growth densities of summer turnip rape plant stands. In Central Europe the main importance is also given to winter turnip rape, which is not as sensitive to pollen beetle damage as the summer variety. The profuse branching of the plant stands treated with natural pyrethrin or left untreated is an indication of the compensatory tendency of plant stands and the limited effect of pyrethrin. Turnip rape also tends to compensate the damage inflicted on embryonic buds by the beetle by producing ad- ditional small buds, which will develop to raceme containing relatively few seeds, as has been re- ported earlier (Nilsson 1988). According to good cultivation practices, the pest control measures against the blossom beetle should include a pyre- thrin spraying as soon as the control threshold for the blossom beetle is exceeded, followed by a sec- ond application using synthetic pyrethroid when the later threshold of two or three insects per plant is exceeded. The aim of the pyrethrin spraying is to reduce the beetle population as effectively as pos- sible (af. Seidel et al. 1991). The second spraying has to be done before the cumulative degreedays value of 3200 C has been reached, to avoid destroy- ing the parasites of the beetles (af. Hokkanen et al. 1988). To optimize the production of the summer turnip rape as an alternative crop for use as non-food raw material and simultaneously to minimize the chemical control and the deleterious and impover- ishing ecological effects on the environment, the following principles should be applied: 1. Only use soil with sufficient pH, and phosphor- ous content 2. A sufficient quantity of fertilizer nitrogen in mineral soil is not higher than 90kg N/ha and in organic soil 70 kg N/ha. 3. Seed dressing not necessary in soils advanta- geous to seedling emergence (light mineral or organic soil) 4. Apply insecticides against rape pollen beetle according to the appearance and abundance of the beetles. 5. Use herbicides only as necessary. 6. Take extreme precautions when using growth regulators especially in combination with couch grass control. Acknowledgements. This research was part of a project of the Ministry of Agriculture, ’The production of rapeseed oil esters for use as diesel fuel’, performed in cooperation with the Finnish rapeseed oil refineries and the Agricultural Re- search Centre. Special thanks are due to the project leader, Prof. Unto Tulisalo, and to the staff of the experimental stations for technical assistance. References Augustin,A., Tulisalo, U. & Korpela, S. 1986. Flea beetles (Coleoptera, Chrysomelidae, Halticinae)on rapeseed and sugarbeet in Finland. J. Agric. Sci. Finl. 58: 69-82. Augustinussen,E. 1987.Kvaelstofgpdskningens indflydelse pä väeksi og udvikling af vårraps: The influence of nitro- gen fertilizing on growth and development of spring oilseed rape. Tidsskr. Planteavl 91: 33-44. Axelsen, J. & Nielsen, P. S. 1990. Compensation in spring sown oilseed rape after attack by pollen beetles. (Me- ligethes aeneus F.) Tidsskr. Planteavl 94: 195-199. Daebeler, F., Röder, K., Hinz, B. & Lucre, W. 1980. Schad- wirkung des Rapsglanzkäfers bei unterschiedlich hohen Stickstoffgaben. Nachr.bl. Pfl.schutz 34: 13-15. Hanus, H.& Schoop,P. 1989. Influence of nitrogen fertilizer and fungicide on yield and yield variability in wheat and barley. In: Anderson, J. R. & Hazell, P. B. R. (eds.). Variability in grain yields: implications for agricultural research and policy in developing countries. Baltimore, Maryland, USA; John Hopkins University Press, p. 265- 269. Hokkanen, H. M. T., Granlund, H„ Husberg, G.B. & Markkula, M. 1986. Trap crops used succesfully to control Meligethes aeneus (Col., Nitidulidae), the rape blossom beetle. Ann. Ent. Fenn. 52: 115-120. —, Husberg, G.-B. & Söderblom, M. 1988. Natural enemy concervation for the integrated control of the rape blos- som beetle Meligethes aeneus F. Ann. Agric. Fenn. 27: 281-294. Köylijärvi, J, & Pahkala, K. 1989. Kevätöljykasvien typ- pilannoitus ja sen ajoittaminen. In: Pahkala, K. (ed.). Öljykasvien viljelyn edistäminen. Maatalouden tut- kimuskeskus Tiedote 11/89.p. 38-51. Kurppa, S. 1991. Betning av vårrybs - 10 års resultat. NJF’s sektion II - Plantedyrkning. Seminar 202. Roskilde, Dan- mark p. 219-223. Lamb, R. J. 1989. Entomology of oilseed brassica crops. 159 Agric. Sd. Fint. 2 (1993) Ann, Rev, Ent. 34: 211-229. Nielsen, P. S, & Axelsen, J, 1988. Spatial distribution of the, pollen beetle ( Meligethes aeneus F.) in spring sown rape (Brassica napus L.) in Denmark, and its importance for sampling. J. Appi. Ent. 105: 35-40. Nilsson, C. 1988. Pollen beetles (Meligethes aeneus F.) and Flowering in rape. Swedish J. Agric. Res, 18: 113-118. Saarela, I. & Köyluärvi, J. 1989. Öljykasvien fosfori- kalium-, rikki-ja boorilannoitus sekä muiden ravinteiden ja kalkituksen tarve. In: Pahkala, K. (ed.). Öljykasvien viljelyn edistäminen. Maatalouden tutkimuskeskus Tie- dote 11/89.p. 52-60. Seidel, D., Kdimati, H. & Daebeler, F. 1991. Reduction of the following generation of pollen beetle by previous insecticide treatment. lOBC/WPRS Bull. 14,6;229-233. & Daebeler, F, 1986. Neue Ergebnisse zur Bekämp- fungsentscheidung bei Rapsschädlingen: Recent results regarding decision making for control of insect pests in rape fields. Nachr.bl. Pfl.schutz 40: 157-160. Tatchell, G. M. 1983. Compensation in spring-sown oil- seed rape (Brassica napusL.) plants in response to injury to their flower buds and pods. J. Agric. Sci., Camb. 101: 565-573. Tulisalo, U. & Wuori, T. 1986. Blossom beetle (Meligethes aeneus Fab. as a yield factor in turnip rape (Brassica camptestris L.) J. Agric. Sci, Finl. 58: 221-237. V IETINGHOFF, J. & Daebeler, F. 1986. Neuere Ge- sichtspunkte bei der Handhabung des Bekämpfungsricht- wertes fur den Rapsglanzkäfer: Recent aspects regarding the standard value for blossom rape beetle control. Nachr.bl. Pfl.schutz 40: 58-61. Wallgren, B. & Radbero, EL. 1989. Crop rotations with and without a ley. Results from trial series R4-1103. Växtodling 1989,No. 13. 26 p. Weber, E. von & Bleiholder, H. 1990.Erläuterung zu den BBCH-Decimal-Codes fur die Entwicklungsstadien von Mais, Raps, Faba-Bohne, Sonnenblume und Erbse - mit Abbildungen. Gesunde Planzen 42: 308-321. Manuscript received February 1993 Sirpa Kurppa Antti Ollula Agricultural Research Centre of Finland Institute of Plant Protection FIN-31600 Jokioinen, Finland SELOSTUS Kevätrypsin tuhohyönteistorjunnan ja typpilannoituksen optimointi Sirpa Kurppa ja Antti Ollula Maatalouden tutkimuskeskus Maatalouden tutkimuskeskuksessa tutkittiin vuosina 1991 ja 1992kevätrypsin kasvinsuojelun ja lannoituksen yhdysvaiku- tuksia. Tuholaistorjunnan tarvetta ei voitu ratkaisevasti vä- hentää lisälannoituksen avulla kasvustoissa, joissa taimettu- misvaiheen kasvutiheys oli noin 300 kasvia/m2. Lisälannoi- tuksen vaikutus tuli esiin parhaimmillaan noin 400 kg/ha sadonlisänä eli huomattavasti vähäisempänä kuin tuhoeläin- totjunnan vaikutus satoon, joka oli parhaimmillaan yli 1000 kg/ha. Rypsi pyrki korvaamaan rapsikuoriaisen vioituksia sivuhaarojen, litujen ja siementen lukumäärää lisäämällä. Vioitusten korvautuvuuden huipputaso saavutettiin jo koh- tuullisella (90 - 110 N kg/ha) lannoitustasolla, jakorvautuva osuus jäi noin 30 % runsaan kuoriaiskannan aiheuttamasta sadon menetyksestä. Sadon menetys korvautui kokonaan, kun kuoriaismäärä ylitti vain niukasti kynnysarvon, 1 kuoriai- nen/kasvi aikaisella nuppuasteella. Kirppojen vioitukset kor- vaantuivat varsin hyvin, mutta rypsin peittaus oli tarpeen kylvösiemenen taimivaiheen tuhojen estämiseksi ja taimettu- misen varmistamiseksi kuivina jaerityisen lämpiminä kausi- na, jolloin kynnysarvo 30 reikää/kasvi ylittyi. Tällöin peit- tauksen laiminlyönti aiheutti torjuntaruiskutuksen tarpeen. Runsaan rapsikuoriaisesiintymän tehokas torjunta edellytti yleensä kahta torjuntaruiskutusta. Kasvunsääteiden ja juola- vehnäntorjunta-aineiden liian intensiivinen käyttö johti sato- tason alenemiseen. Kohtuullinen lannoitustaso (90 - 110 kg N/ha) oli riittävä parhaan katetuoton saavuttamiseksi jopa raskailla kivennäismailla. 160 Agric. Sei. Fint. 2(1993)