Sustainable management of two key pests of cabbage, Brassica oleracea var. capitata L. (Brassicaceae), using homemade extracts from garlic and hot pepper K. O. Fening, B. W. Amoabeng, I. Adama, M. B. Mochiah, H. Braimah, M. Owusu-Akyaw, E. Narveh & S. O. Ekyem Organic Agriculture Official journal of The International Society of Organic Agriculture Research ISSN 1879-4238 Volume 3 Combined 3-4 Org. Agr. (2013) 3:163-173 DOI 10.1007/s13165-014-0058-2
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Author's personal copy Org. Agr. (2013) 3:163–173 DOI 10.1007/s13165-014-0058-2
Sustainable management of two key pests of cabbage, Brassica oleracea var. capitata L. (Brassicaceae), using homemade extracts from garlic and hot pepper K. O. Fening & B. W. Amoabeng & I. Adama & M. B. Mochiah & H. Braimah & M. Owusu-Akyaw & E. Narveh & S. O. Ekyem Received: 20 September 2012 / Accepted: 10 January 2014 / Published online: 9 February 2014 # Springer Science+Business Media Dordrecht 2014
Abstract Cabbage, Brassica oleracea var. capitata L., is an important leafy vegetable that provides vitamins and minerals for healthy body development. However, insect pest attack is a key contributing factor to its low yield. An experiment was undertaken at the agricultural research field of Crops Research Institute, Council for Scientific and Industrial Research (CSIR), Kwadaso in Ghana, during the major seasons of 2010 and 2011 to explore the potential of homemade extracts from garlic, Allium sativum L., and hot pepper, Capsicum frutescens L., in the management of insect pests of cabbage. Emamectin benzoate (ATTACK®) and lambdacyhalothrin (BOSSMATE® 2.5EC) were used as reference insecticides. There were ten treatments made up of three levels (10, 20 and 30 g L−1 w/v) each of garlic, pepper, a mixture of garlic and pepper, ATTACK®, BOSSMATE® and control (tap water). The key insect pests recorded were the aphid, Brevicoryne brassicae L., and the diamondback moth, Plutella xylostella L. Generally, the efficacy of garlic and pepper was comparable to that of ATTACK®, with BOSSMATE® being
the least efficacious. Pepper (20 g L−1 w/v) and ATTA CK® (1 ml L−1 v/v) were more effective in controlling P. xylostella than the other treatments. Natural enemies encountered were the Coccinellidae, Syrphidae and Araneae. Generally, BOSSMATE® caused the greatest reduction in natural enemies’ abundance, followed by ATTACK®, with the plant extracts having a mild effect on the natural enemies. Cabbage head yield was comparable among insecticide-treated plots and botanical plots with the control plots doing well in some instances. Garlic and pepper offer a significant potential for further exploration and development into affordable plant protection products for cabbage pests’ management, especially in smallholder farms and backyard gardens and organic vegetable production systems.
K. O. Fening : B. W. Amoabeng : I. Adama : M. B. Mochiah : H. Braimah : M. Owusu-Akyaw : E. Narveh : S. O. Ekyem Crops Research Institute, CSIR, P. O. Box 3785, Kumasi, Ghana
Cabbage, Brassica oleracea var. capitata L. (Brassicaceae), is an exotic leafy vegetable known to originate from Western Europe (FAO 2000). Its cultivation has now become an important source of livelihood for small-scale farmers in the rural, peri-urban and urban areas in Ghana due to its growing popularity for home consumption and the food industry (Abbey and Manso 2004; Mochiah et al. 2011; Baidoo et al. 2012). Cabbage is rich in mineral salts, vitamins and proteins for healthy body development (USDA 2009). It is consumed raw or
K. O. Fening (*) Soil and Irrigation Research Centre, Kpong, Institute of Agricultural Research, College of Agriculture and Consumer Sciences, University of Ghana, P. O. Box LG. 68, Accra, Ghana e-mail:
[email protected]
Keywords Cabbage pests . Plant extracts . Natural enemies . Sustainable management
Introduction
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in sauces (stew and soup) or in salads, sandwiches and hamburgers (Baidoo et al. 2012). However, attack of cabbage by insect pests in the field affects its yield, quality and market value (Zehnder et al. 1997; Fening et al. 2011). Among the insect pests of the crop in Ghana include the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae); the cabbage webworm, Hellula undalis F. (Lepidoptera: Crambidae); the cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae); the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae); the flea beetles, Phyllotreta spp. (Coleoptera: Chrysomelidae); the whitefly, Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae); and the variegated grasshopper, Zonocerus variegatus (L.) (Orthoptera: Pyrgomorphidae) (Mochiah et al. 2011; Fening et al. 2011; Baidoo et al. 2012). A study conducted in southwestern Ontario in Canada concluded that attack by insect pests alone contributed significantly to yield loss of cabbage by 50 % (Tolman et al. 2004). For instance, DBM which is a cosmopolitan pest of crucifers caused a significant yield loss of 20–100 % and up to 60 % on cabbage in India and Ghana, respectively (Chellaiah and Srinivasan 1986; Lingappa et al. 2004; Obeng-Ofori et al. 2007). Consequently, the global cost of control of DBM has recently been estimated between US$4 and 5 billion (Zalucki et al. 2012). Frequent application of pesticides is the main management strategy by farmers in Ghana (Ntow et al. 2006). The problems associated with the use of synthetic pesticides include the development of insecticide resistance; destruction of non-target organisms such as beneficial insects (pollinators and natural enemies); contamination of farm produce with insecticide residues due to improper application techniques, mostly by inexperienced farmers; exposure of the user to risks of chemical poisoning; and environmental contamination (Obeng-Ofori et al. 2002; Timbilla and Nyarko 2004; Ntow et al. 2006; Fening et al. 2011). The numerous problems associated with the use of synthetic insecticides for insect pest management had led to the search for alternative options for managing insect pests in a more sustainable manner. Thus, organic cabbage farming is increasingly becoming a nature-friendly and well-embraced farming system as opposed to conventional farming which relies heavily on chemical inputs (Baidoo et al. 2012). Organic cabbage farming has added advantages such as
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conserving natural enemies of pests, maintaining ecological balance and integrity of the crop and promoting food and environmental safety (Fening et al. 2011; Osei et al. 2013). Despite the benefits of organic farming, one of the challenges has been the availability of acceptable, user-friendly technologies for easy incorporation into organic farming systems (Osei et al. 2013). Key focus will be the development and promotion of pest control products from plant origin (Fening et al. 2011). Consequently, the use of natural plant products for pest management is a promising option that has recently attracted a lot of attention worldwide (Ascher 1996; Zehnder et al. 1997; Obeng-Ofori and Ankrah 2002; Okoth et al. 2002; Antonious et al. 2007; Davis 2007; Mochiah et al. 2011). The way forward is to produce effective homemade plant protection products that are readily available, cheap and safe to the environment, wildlife and consumers for adoption by the small-scale vegetable growers. This study investigates and discusses the potential of using homemade extracts from garlic, Allium sativum L. (Alliaceae), and hot pepper, Capsicum frutescens L. (Solanaceae), in the management of insect pests of cabbage in organic production systems, especially smallholder farms and backyard gardens.
Materials and methods The study was undertaken from June to September 2010 and 2011 at the experimental field of Crops Research Institute (CRI), Council for Scientific and Industrial Research (CSIR), at Kwadaso in Kumasi, Ghana. During the period of the trials, the temperature range at Kwadaso was 29–32 °C with a relative humidity of 70–80 %. Kwadaso falls within longitude 1° 40′ W and latitude 6° 42′ N and lies 262 m above sea level. This area is part of the moist semi-deciduous forest ecological zone of Ghana with annual rainfall between 1,200 and 1,600 mm. The soil type is sandy loam. Certified healthy hybrid white cabbage (B. oleracea var. capitata L.) (cv. oxyrus) seeds (obtained from a local retail shop, Abnark Agro Services, Kumasi, Ghana) were sown on a raised bed in the field on June 1, 2010 and 2011. The young seedlings were protected from attack by insect pests and snails with mosquito-proof net (1.2 mm×1.2 mm mesh size). These were transplanted onto raised beds in the main field at a stage of 4 weeks. The field layout was a
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randomized complete block design with three replications. There were ten treatment plots. Each plot (5 m× 2 m) had four rows, with each row having ten plants. The inter- and intra-row spacing was 0.50×0.50 m with the inter plot distance of 3 m. The different treatments were as follows: (1) 10 g of garlic L−1 w/v, (2) 20 g of garlic L−1 w/v, (3) 30 g of garlic L−1 w/v, (4) 10 g of pepper L−1 w/v, (5) 20 g of pepper L−1 w/v, (6) 30 g of pepper L−1 w/v, (7) 10 g of garlic+10 g of pepper L−1 w/v, (8) 2.4 ml L−1 v/v of BOSSMATE® 2.5EC (lambda-cyhalothrin), (9) 1 ml L−1 v/v of ATTACK® (emamectin benzoate) and (10) control—tap water. The three different rates of pepper and garlic in ascending order will hereafter be referred to as pepper 1, pepper 2, pepper 3, garlic 1, garlic 2 and garlic 3. The stalks of ripened hot pepper and the outer cover of the cloves of garlic were removed. The specific weights were obtained using an electronic balance and then ground separately using an electric blender. The resultant mixture was sieved using a fine linen material and left overnight for use the following morning. A few drops of natural oil and local soap (Alata Samina) were added to the mixture to enhance its delivery and stickiness onto the leaf surface. This mixture was further diluted with water to the required volume for spraying using a CP-15L knapsack sprayer. There was an application into the soil of a well-decomposed poultry manure (NPK levels of 2.20:1.80:1.10, respectively), at 20 t/ha equivalent to 250 g per plant furrow, 2 weeks before transplanting of seedlings. The treatments were applied 10 days after transplanting of seedlings and were repeated weekly until the cabbage heads were fully formed. For each treatment, ten plants were sampled from the two innermost rows for assessment of pests. The number of insect pests, aphids and DBM on each plant was counted. Cabbage aphids were much more numerous and difficult to count without disruption, so they were scored as follows: 0=absent, 1=a few scattered individuals, 2=a few isolated small colonies, 3=several small isolated colonies, 4=large isolated colonies and 5=large continuous colonies (Afun et al. 1991). Similarly, the number of natural enemies (ladybirds, hoverflies and spiders) were counted. The data were taken weekly 3 days after the application of treatments between 6 and 8 a.m. At harvest, 16 plants per treatment plot were selected from the two innermost rows (eight plants from each row, minus the border plants) for yield and multiple head damage assessment. The number of cabbages with
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multiple heads was counted, and head weight was taken. All useful cultural and agronomic practices were employed during the period. The data were subjected to ANOVA using repeated measures procedure of SAS (SAS Institute Inc. 2011). Mean separation was done using the Student NewmanKeuls (SNK) test (P
