The diamondback : a problem pest of brassica crops in Kenya

G. N. Kibata Kenya Agricultural Research Institute, P O Box 57811, Nairobi, Kenya

Abstract Cruciferous crops are important vegetables in Kenya for local consumption, export and processing (dehydration and oil extraction). They grow well on a wide variety of soils wherever water is available. One major limiting factor to successful production of these vegetables is the diamondback moth (DBM), xylostella L. (: Yponomeutidae). The larvae are voracious defoliators with a potential to destroy entire crops if not effectively controlled. Host resistance, endemic biocontrol agents and cultural practices have not been fully exploited in the management of DBM in Kenya. The easier option has been the use of spurious amounts of chemical . In the early 1970s, organochlorines such as DDT afforded satisfactory control of DBM. In subsequent years, several carbamate-based products achieved excellent control of the pest. With the advent of synthetic in 1980s, DBM appeared to have been completely subdued. Recent resurgences of the pest and progressive control failure herald intrinsic changes in DBM which make the pest less susceptible to the available chemical arsenal. This paper reports on screening trials, undertaken, on farm, to assess efficacy of various products on DBM. It also alludes to circumstantial evidence of pest resistance to popularly used pesticides and is a prognosis for development of more sustainable control strategies.

Key words: DBM, chemical control, Brassica, Kenya.

Introduction The following organisms have been recorded as Brassica crops, which include , , brussel natural enemies of DBM in Kenya: sprouts, , and rape seed, are important vegetables in Kenya, largely grown for local Predators consumption, export and processing (dehydration and Birds oil extraction). While most of the production is in the Spiders small holder sector, commercial production is on the Ants - Pheidole sp. increase, especially, for . Available statistics Hover flies Syritta sp. and Melanostoma sp. (Diptera: indicate that, collectively, brassicas are grown on over Syrphidae) 40,000 hectares with a production of 604,000 metric tonnes, valued at Kenya £104 million. (MALDM, 1988). Diadegma molliplum (Holmgren) The crops grow well on a wide range of soils and (= Stellenboschensis Cameron) agro-ecological zones, wherever water is available. A (Hymenoptera: Ichneumonidae) major production constraint is the diamondback moth Diadegma sp. (Hymenoptera: Ichneumonidae) (DBM) Plutella xylostella L. (Lepidoptera: Itoplectis melanospilla Cameron (Hymenoptera: Yponomeutidae). The larvae of DBM are voracious Ichneumonidae) defoliators which could destroy an entire crop if left Hemiteles sp. (Hymenopteran: Ichneumonidae) uncontrolled. DBM was first recorded as a Diplazon sp. (Hymenoptera: Ichneumonidae) cosmopolitan agricultural pest in 1746 (Harcourt, Brachymeria apantelesi Ribsec (Hymenoptera: 1962). The presence of feeding stimulants (mustard Chalcididae) glucosides) and the absence of chemical inhibitors Pteromalus sp. (Hymenoptera: Pteromalidae) restrict the oligophagous larvae of DBM to the mustard Tetrastichus sokolowskii Kurdjumov (Hymenoptera: type of plants, the Cruciferae (Thornsteinson, 1953). Eulophidae) It has been recognised that host plant resistance, Macrogaster sp. (Hymenoptera: Braconidae) use of natural enemies and management of the crop Carducia plutella Emd (Diptera: Tachinidae) agroecology could alleviate problem of DBM (Ullyett, 1947). Several natural enemies of DBM have been Entomophagous fungi recorded in Kenya (Le Pelley, 1959; Kibata, 1978). Possibly Entomophthora sphaerosperma Fres. (= Zoophthora radicans, Brefeld) has been found to cause epizootics on DBM under favourable conditions. The fungus has potential to control DBM (Wang’endo,

Status of DBM and other pests of crucifers and their biocontrol 47 1994). However, given the easier option of using Results chemical pesticides, little attempt has been made to The collective results of the four trials demonstrated exploit other pest control strategies. that there are significant differences between On a global scale the cost of managing DBM is treatments (p <0.05) with regard to DBM infestation, currently estimated at USD 1 billion through the use numbers of marketable cabbage heads and related yield of pesticides (Talekar et al., 1992). In South East , (Tables 1, 2, 3, & 4). Whilst the DBM infestation varied the prodigious use of pesticides to control DBM has between the trials, higher infestation was observed in resulted in the typical pesticide treadmill where first and fourth trial runs. The trend was, however, shifting and changing of chemicals no longer solves consistent with respect to efficacious products in the problem. comparison with untreated control plots. Mean DBM In Kenya chemical control of DBM was infestation was highest in control plots where yield of successfully undertaken with organochlorine marketable cabbage was also lowest in all instances. , such as DDT, lindane and endosulfan, in Effective products more than doubled the yield 1970s. In later years carbamates became more popular, of cabbage, which confirms the need to evolve such as carbaryl, cartap hydrochloride, acephate and effective management strategies for DBM. carbofuran. With the advent of synthetic pyrethroids On the basis of DBM suppression and cabbage in 1980s, DBM became a problem of the past, as yield the test products could be classified as follows: dramatic control of the pest was achieved (Kibata, 1978). Very effective Recently, however, the scencario has been ¥ Secure¨ (AC 303630) - , acaricide gradually changing as more intensive production of trifluoromethyl brassicas and rampant usage of pyrethroids continues. pyrrole carbonitrile Reports on control failure for DBM were on the ¥ Fipronil - phenyl pyrazole increase, prompting further search for products with insecticide, acaricide varied modes of action. This paper reports on recent ¥ Prothiofos (Tokuthion¨) - organophosphate (OP) trials undertaken to evaluate new and old products for ¥ BtXentari¨ - , this purpose. There is, however, no claim that the DBM Berliner subsp. problem is resolved. aizawai ¥ Novaluron¨ (MCW-275) - Benzoylphenyl urea Materials and Methods (IGR) Four series of trials were conducted at two farms in the north coast of Naivasha (0° 43' 40"S, 36° 24', 32"N, Effective 1921m asl) from April 1994 to May 1995. The trials ¥ Methidathion - organophosphate design was CRBD with three replicates, whilst ¥ Methomyl + Methidathion - carbamate/OP treatments ranged from 19 to 21 entries, inclusive of ¥ Methomyl - carbamate untreated checks (controls). Seedlings of cabbage ( var. Least effective capitata) variety Gloria were transplanted into plots ¥ Methamidophos - organophosphate at row and plant spacing of 60 cm and 30 cm ¥ Cypermethrin - respectively. Inter block and inter plot paths were 2 m ¥ Acephate - carbamate and 1m, respectively. ¥ Fenpropathrin - pyrethroid Plant stand counts for the four trials were 60, 130, ¥ Neem powder - Botanical 99 and 105 per plot, respectively, exempting guard ¥ Etofenprox (Trebon¨) - non-ester pyrethroid rows. Fertilizer was applied as recommended for cabbage at transplanting and subsequently as top Discussion dressings. Results of these trials subscribe to the view that Once the seedlings were established, weekly pyrethroids which have been extensively used are no samplings for immature DBM were undertaken on five longer as effective as they used to be whilst products cabbages per treatment plot. Application of test from new chemistry appeared extremely effective insecticides were made fortnightly using a CP3 against DBM. knapsack sprayer with a hollow cone nozzle calibrated Among the most effective products, Secure¨ (AC to deliver 400 litres of spray per hectare. 303630) is an insecticide and acaricide from Cyanamid At maturity all marketable cabbage heads were based on 4-bromo-2-(4-chloropheny)-1-ethoxymethyl- harvested, counted and weighed for assessment of 5-trifluoromethylpyrrole-3=carbonitrile. Fipronil is a yield. The pooled means of DBM counts for immatures phenyl pyrazole insecticide acaricide from Rhone- over the crop season, numbers of marketable cabbage Poulenc. Prothiofos is an old OP insecticide from heads and yield was subjected to ANOVA and DMRT Bayer while Bt Xentari is a new insecticide based on to assess effects of treatments on these parameters Bacillus thuringiensis, Berliner subspecies aizawai (Tables 1, 2, 3, 4). from the same company. Novaluron (MCW-275) is a novel benzoylphenyl urea from Makhteshim Agan. Evidently, the modes of action of these products are

48 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests Table 1. Effect of treatments on DBM infestation and cabbage yield at Aberdare farm, (Trial period 20/04/94 to 01/06/94) (plant population 60)1

Treatments Rate Mean Mean Mean g.a.i. ha-1 DBM marketable cabbage yield counts heads (kg) per plot

1. Untreated Ð 17.01a 9.7a 5a 2. Acephate 750WP 600 6.67fg 33def 36fg 3. Fipronil 50 SC 12.5 5.87gh 35fg 46hij 4. Fipronil 50 SC 25 4.81h 42g 54ij 5. Fipronil 50 SC 50 2.05i 50h 75k 6. Etofenprox 200 Ec 100 11.02bc 16ab 11ab 7. Chlorpyrifos 480 Ec 384 11.40b 20bc 14bc 8. Dichlorvos 500 Ec 400 10.10cd 20bc 17bc 9. Thiodicarb 375 Ec 562.5 8.69e 23bcd 19bcd 10. Methomyl 900 SP 360 7.34f 33ef 36fg 2 11. “Secure” 360 SC 144 1.50i 42g 71k 12. Cypermethrin 50 Ec 50 8.61e 29cdef 32efg 13. Methidathion 400 Ec 240 5.88gh 28cdef 31ef 14. Methidathion 200 + Methomyl 50 Ec 150 9.11de 31def 37fgh 15. Methidathion 200 + Methomyl 50 Ec 200 5.02h 32def 41ghi 16. Pyrethrins 60 Ec 36 12.20b 28cdef 34efg 3 17. Bt Xentari 1000g 4.75h 33f 50ij 18. Methamidophos 600 SC 360 7.28f 24bcde 27de 19. Methidathion 200 + Methomyl 50 Ec 300 7.29f 23bcd 20cd 1Means followed by the same letter within the same column are not significantly different (P > 0.05) by DMRT 2Secure” proposed common name for AC 303630 3Bt Xentari 15x103 I.U.mg-1 (Bacillus thuringiensis subsp. aizawai) 1000g of product applied per hectare

Table 2. Effect of treatments on DBM infestation and cabbage yield at Aberdare farm, (Trial period 06/06/94 to 17/08/94 (plant population 130)1

Treatments Rate Mean Mean Mean g.a.i/ha DBM marketable cabbage Yield counts heads (kg) per plot

1. Untreated Ð 2.80a 62.7a 144a 2. Acephate 750 WP 600 0.89ef 83ab 242cd 3. Fipronil 50 SC 12.5 0.40hi 97bc 280cde 4. Fipronil 50 SC 25.0 0.37hij 127def 342efg 5. Fipronil 50 SC 50.0 0.27hij 129def 387efg 6. Etofenprox 200 Ec 200 1.85b 63a 152ab 7. Prothiofos 960 Ec 768 0.25hij 128def 410gh 2 8. Azadirachtin 1.5 L 1.65c 66a 152ab 9. Thiodicarb 375 Ec 562.5 1.92b 63a 157ab 10. Methomyl 900 SP 360 1.08d 82ab 229bc 3 11. “Secure” 360 SC 144 0.21i 127def 445h 12. Cypermethrin 50 Ec 50 1.12d 83ab 216bc 13. Methidathion 400 Ec 20 0.67g 99bcd 248cd 14. Methidathion 200 + Methomyl 50 Ec 150 0.44h 100bcde 300de 15. -ditto- 200 0.41hi 102bcdef 305de 16. -ditto- 300 0.24ij 112cdef 335ef 4 17. Azadirachtin Ec 2 g/plant 0.76fg 89abc 240cd 5 18. Bt Xentari 1 000 0.22ij 127def 405gh 19. Methamidophos 600 Sc 600 1.02de 75ab 217bc 1Means followed by the same letter within the same column are not significantly different (P > 0.05) by DMRT. 2Neem seed liquid extract (JAWAN¨) from India applied at 1.5 litres per hectare. 3“Secure” proposed common name for AC 303630. 4Neem seed powder (locally produced) 2% a.i. applied at 2g/plant. 5Bt (Xentari) 15x103 I.U. mg-1 (B.t. subsp. aizawai) applied 1000g/ha. different from that of pyrethroids which are relatively of cabbage (r2 = 0.61) (Y = 236.91 Ð 0.198x). This is ineffective on DBM at Naivasha. an expected outcome as heavily infested cabbage failed From results of the last trial it was shown that to form heads or formed heads which could not be DBM infestation was significantly related (P < 0.001) marketed. with numbers of marketable cabbage heads (r2 = 0.69) It is therefore pertinent to conclude that DBM (Y = 87.99 Ð 7.013x) as well as the marketable weight causes substantial economic loss in cabbage

Status of DBM and other pests of crucifers and their biocontrol 49 Table 3. Effect of treatments on DBM infestation and cabbage yield at Boffar farm, Naivasha, (Trial period 31/08/94 to 14/10/94) (plant population 99)1

Treatments Rate Mean Mean Mean g.a.i./ha-1 DBM marketable cabbage counts heads yield (kg) per plot

1. Untreated Ð 2.83a 49a 39abc 2. Acephate 750 WP 600 0.96d 57abc 68cd 3. Fipronil 50 SC 12.5 0.63fg 58abc 104gh 4. Fipronil 50 SC 25.0 0.46hi 67e 106gh 5. Fipronil 50 SC 50.0 0.25j 70cd 105gh 6. Etofenprox 200 Ec 200 1.55b 50ab 25a 7. Prothiofos 960 Ec 768 0.28j 90e 180j 2 8. Azadirachtin 1.5 L 1.36c 52ab 58bc 9. Thiodicarb 375 Ec 562.5 1.35c 51ab 56bc 10. Methomyl 900 SP 360 0.97d 57abc 68cd 3 11. “Secure” 360 SC 144 0.31ij 87e 130i 12. Cypermethrin 50 Ec 50 0.87de 65bc 91fg 13. Methidathion 400 Ec 320 0.67fg 59abc 90fg 14. Methidathion 200 + Methomyl 50 Ec 300 0.57gh 61abc 60c 15. Novaluron 100 Ec 5 0.75ef 60abc 83def 16. Novaluron 100 Ec 10 0.57gh 58abc 82def 4 17. Azadirachtin 2g/plant 0.87de 58abc 93fgh 5 18. Bt Xentari 1000g 0.56gh 80de 112hi 19. Methamidophos 600 SC 600 0.59fgh 58abc 69cde 6 20. Bt Xentari 500g 0.99d 63abc 89efg 1Means followed by the same letter, in the columns, are not significantly different (P > 0.05) by DMRT. 2Neem seed liquid extract (JAWAN¨) from India applied 1.5 litres ha-1 3“Secure” proposed common name for AC 303630. 4Neem seed powder (locally produced) applied at 2g/plant. 5&6Bt (Xentari) 15x103 I.U. mg-1 B.t. subsp. aizawai applied at 500g and 1000g product ha-1.

Table 4. Effect of treatments on DBM infestation and cabbage yield at Aberdare farm, (Trial period 05/04/95 to 17/05/95) (plant population 105)1

Treatments Rate Mean Mean Mean g.a.i./ha-1 DBM marketable cabbage yield counts heads (kg) per plot

1. Untreated Ð 18.39a 2.00h 0.60g 2 2. Acephate 970 776 9.73ef 2.33h 1.47g 3. Fipronil 50 SC 12.5 6.91g 49.00de 99.67def 4. Fipronil 50 SC 25.0 5.00ij 66.00c 148.60cd 5. Fipronil 50 Sc 50.0 3.55k 90.00ab 269.70ab 6. Prothiofos 960 Ec 768 10.58de 3.67h 2.70g 3 7. “Secure” 360 SC 144 2.30l 94.67a 320.70a 8. Cypermethrin 50 Ec 50 13.64b 0.67h 0.13g 9. Methidathion 400 Ec 320 5.79hi 39.33efg 65.33defg 10. Methidathion 200 + Methomyl 50 Ec 300 6.09gh 29.67fg 53.67efg 11. Novaluron 100 Ec 5 5.97h 34.00fg 93.17def 12. Novaluron 100 Ec 10 4.76i 51.67d 143.80cde 4 13. Bt Xentari 500g 5.61hij 40.67ef 98.53def 14. Bt Xentari 1000g 3.79k 81.67b 217.30bc 15. Methamidophos 600 Sc 600 6.94g 28.67g 47.17fg 16. Triflumuron 480 SC 240 10.67dc 2.33h 2.53g 17. Fenpropathrin 100 Ec 100 9.97e 1.00h 0.43g 18. Fenpropathrin 100 Ec 50 11.30cd 0.33h 0.17g 19. Beta-cyfluthrin 25 Ec 15 8.88f 0.67h 0.47g 20. Endosulfan 475 FL 475 11.61c 1.00h 0.37g 21. Carbosulfan 250 Ec 250 10.58de 0.33h 0.17g 1Means followed by the same letter within columns, are not significantly different (P > 0.05) by DMRT. 2Acephate (97% pellets) 3“Secure” proposed common name for AC 303630 4Bt (Xentari) 15x103 I.U. mg-1 Bt subs. aizawai applied at 500 and 1000g ha-1

50 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests 18 Plutella counts 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Treatments

240 Mean yield in kg 220 200 180 160 140 120 100 80 60 40 20 0 12345 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Treatments Figure 1. Mean counts of DBM and yield in various treatments (refer table 1) in Trial 1 production. Some commercially available pesticides Acknowledgement are no longer affording the level of desired control on The author wishes to gratefully acknowledge the DBM. Products under development, whose mode of assistance of Messrs S. O. Pete and J. W. Kamau who action is novel, appear to be extremely effective on assisted in the implementation of the trials and DBM. This heralds a warning that pest resistance to Margaret Gitonga who diligently typed the manuscript. popular insecticides may have developed in the The work would have been impossible without the diamondback moth. The need to develop a financial and moral support of the KARI/ODA Crop comprehensive strategy for better management of Protection Project. Preparation of this paper has been DBM is therefore advocated if successful production duly authorised by the Director, Kenya Agricultural of Brassica crops is to be sustained in Kenya. Research Institute (KARI). The author is gratefully It is also noted that previous work on identification indebted to the GTZ-IPM Horticulture project for the of other major mortality factors for DBM identified sponsorship to this conference. several natural enemies. These were only collected from farms where no pesticides were being used or References where there were adequate refugia in wild cruciferous Harcourt, D.G. (1962). Biology of cabbage caterpillars in weeds or neglected Brassica crops. The natural Eastern Ontario. Proc. Entomol. Soc. Ont. 93: 61Ð65. enemies did not however appear to confer satisfactory Kibata, G.N. (1978). Control of Diamondback moth suppression of DBM on their own. An integrated caterpillars on cabbage p. 15–18. Senior Entomologist’s Annual Report. 60pp. approach to the management of DBM should therefore Le Pelley, R.H. 1959. Index of hosts of parasites: be explored. Plutella maculipennis - p.245. In Agricultural of East . E.A. High Comm. Nairobi, Kenya 307pp.

Status of DBM and other pests of crucifers and their biocontrol 51 Plutella counts 3 2.8 2.6 2.4 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 152 3 4 6 7 8910 11 12 13 14 15 16 17 18 19 Treatments 1.4 Mean yield in kg 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Treatments Figure 2. Mean counts of DBM and yield in various treatments (refer table 2) in Trial 2 Plutella counts 3 2.8 2.6 2.4 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1234567891011121314151617181920 Treatments 600 Mean yield in kg

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0 1234567891011121314151617181920 Treatments Figure 3. Mean counts of DBM and yield in various treatments (refer table 3) in Trial 3

52 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests Plutella counts 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 145623 7 8131491011 12 15 16 17 18 19 20 21 Treatments

Mean yield in kg 350

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0 1423 567 8131491011 12 15 16 17 18 19 20 21 Treatment Figure 4. Mean counts of DBM and yield in various treatments (refer table 4) in Trial 4 MALDM (1988). Crop Production statistics. Min. of Agric. Liv. Dev & M. Kenya. Talekar, N.S., J.C. Yang, and S.T. Lee, (1992). Introduction of to control diamondback moth in Taiwan. In “Diamondback moth and other crucifer pests, Proceedings of the Second International Workshop, Tainan, Taiwan. Talekar, N.S. (ed.), pp. 263Ð 270. AVRDC. Thorsteinson, A.J. (1953). The chemotactic reponses that determine host specificity in an oligophagus insect (Plutella maculipennis (Curt) Lepidoptera). Can. J. Zool. 31: 52Ð72. Ullyett, G.C. (1947). Mortality factors in populations of Plutella maculipennis Curtis and their relation to the problem of control. Entomol. Mem. Dept. Agr. S. Africa. 2: 77Ð202. Wang’endo, L. (1994). Interactions between the insect growth regulator, Flufenoxuron (CASCADER;); the entomopathogen, Zoophthora radicans Brefeld and the Diamondback moth Plutella xylostella L. MSC thesis, Univ. of Bristol, United Kingdom.

Status of DBM and other pests of crucifers and their biocontrol 53