INDUSTRIAL CROPS ANDPRODUCTS zyxwvutsrq AN INTERNATIONAL ELSEVIER JOURNAL Industrial Crops and Products 5 (1996) 307-322 Pyrethrum (Chrysanthemum cinerariaefolium Vis.) cultivation in West Kenya: origin, ecological conditions and management F?Wandahwa a, E. Van Ranst a,*,I? Van Damme b a University zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Ghent, Department of Geology and Soil Science, Laboratory of Soil Science, Krijgsluan 281/S8, 9000, Ghent, Belgium b University of Ghent, Faculty of Agricultuml and Applied Biological Sciences, Department of Crop Production, Coupure Links 653, 9000, Ghent, Belgium Received 17 April 1996; accepted 8 July 1996 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR Abstract Pyrethrum (Chrysanthemum cineruriaefoZium) is a small perennial plant commercially grown for extraction of natural pyrethrins used to make insecticides. This paper discusses the use and distribution of pyrethrum, the ecological requirements and agronomic practices in West Kenya, with emphasis on managementconstraints and further research. The responses to nitrogen, phosphorus and potassium fertilizers are reviewed. These responses are not yet well understood and require further research. Diseases, pests and weeds of pyrethrum and their control are mentioned. Further research on application of herbicides is required. Farmers grow pyrethrum in less favourable climatic conditions. Yields are low and influenced by producer prices. Research should therefore focus on increasing yields and reducing labour demands without sacrificing the high pyrethrins’ content typical for Kenyan pyrethrum. Model-oriented research on crop phenology, light interception, light use efficiency, biomass growth and partitioning and water use efficiency could shorten the duration and lower the costs of experiments in potential yield exploration when introducing pyrethrum among existing agricultural systems. Strong campaigns against synthetic insecticides that pollute the environment are required in order to increase pyrethrum demand, and thus production and use. Keywords: Pyrethrum; Ecological conditions; Agronomic practice; Research priority; West Kenya 1. Introduction Pyrethrum (Chrysanthemum cinerariaefolium) is a small perennial plant cultivated for extraction of pyrethrins from the dried flower achenes. Pyrethrins are a group of six active chemical ingredients of acids and alcohols used in the manufacture of insecticides (Chandler, 1951; Head, 1966, 1969). The use of pyrethrum flowers for insecticidal purposes originated in Persia. Chrysanthemum coccineum was the *Corresponding author. Fax: +32 (9) 264-4997. first species to be used. It was introduced into Europe in the 19th century and into the United States about 1860. Later, C. cinerariaefolium, probably the correct name being Tanacetum cinerariifolium (Purseglove, 1982) was found to be more effective and became the main source of pyrethrum. Originally, dried capitula were powdered for use, but replaced by kerosene extracts around 1920. The use of pyrethrum was much extended in the 1930’s and assumed great importance during the second world war when it was used in mosquito repellent cream and ointment against scabies. It was 0926-6690/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PI1 SO 926- 6690(96)00032- S 308 f? Wandahwa et al./Industrial found to be effective against flies, fleas, lice and mosquitoes. It was also used to protect food and other produce. At present, it is used in livestock sprays, in fog generators to protect warehouses and in mosquito sprays and coils for burning. Pyrethrum solutions are used for dipping dried fish and meat against beetle infection with Dermestes species and blow flies, Cdiphoru species (Purseglove, 1982). Despite the post war development of DDT and other chlorinated hydro-carbon and organophosphorus insecticides, pyrethrum has maintained a superior position as a natural insecticide. It is effective against a wide range of insects with little development of resistant strains. It has a rapid paralytic action or knock-down effect. It is low in toxicity to mammals and other warm blooded animals and free from taint. It is non-inflammable and leaves no oily residue (Elliot et al., 1969; Purseglove, 1982). For these reasons, it is particularly valuable for use in the home and where there are foodstuffs. With the use of synergists such as sesame oil, piperonyl butoxide and others, the cost of application is reduced. The synergists are not insecticidally active, but have the properties of enhancing the toxicity of pyrethrins and thus reduce the amount that is needed to achieve a given level of insecticidal activity. Apart from its use as an insecticide, pyrethrum mart, the flower grist that remains after extraction of pyrethrins, is used as an animal feed. This animal feed is marketed in Kenya under the name ‘Pymac’ and has the same nutritive value as wheat bran or pollard (Kayongo-Male and Abate, 1989; Mathur et al., 1961). This paper discusses the cultivation of pyrethrum in West Kenya and identifies areas of interest that require further research in order to improve farming conditions and increase yields among small scale farmers who are the majority cultivating this crop. Crops and Products 5 (1996) 307-322 Seeds from Switzerland and Japan were grown in England at Rothamsted Experimental Station from 1924 onwards. The station supplied seeds of the Harpenden strain to Kenya in 1929. In the same year, seeds were obtained from Dalmatia by the first farmer to grow pyrethrum commercially in Kenya. The second world war completely stopped supplies of pyrethrum from Japan leaving Kenya the world’s largest producer from 1945 till today. With increased demand during the war, production was extended to the highlands of Tanzania and Kigezi in southwestem Uganda. Pyrethrum has been tried in many countries including Rwanda, Ecuador, India, Zaire, Papua New Guinea, Nepal, China and Brazil (Ministry of Agriculture, 1992). At present, the world’s second largest producer is Australia where it is grown intensively in the southern State of Tasmania. This fully mechanized production system in Tasmania was developed by CIG Pyrethrum, part of the world-wide multinational company BOC Gases Limited. The pyrethrum industry in Australia was started when in the 1970’s a special pest control product ‘Pestigas’ based on synergised pyrethrins was developed. Around the same time, the University of Tasmania commenced a pyrethrum breeding program with genetic material from India. By 1980, several high yielding cultivars that produce one single flush of flowers and are suitable for mechanical harvesting had been produced. Further trials by CIG Pyrethrum allowed it to develop a fully mechanized, commercial production system, the first of its kind in the world. In 1986, the area planted was increased and at present CIG Pyrethrum contracts 85 farmers in northwest Tasmania, the Coal River Valley and the Derwent River Valley to grow pyrethrum on 1200 ha. Production has increased from 300 tons of flowers in 1989 to 2500 in 1993 giving CIG Pyrethrum a 10 to 20% share of the world market (CIG Pyrethrum, 1995). 2. Origin zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA and distribution 3. EcologlcaI conditions Chrysanthemum cinerariaefolium occurs in the wild on the Dalmatian coast of former Yugoslavia. 3. I. Climatic conditions It was introduced into Japan in 1881, which became the principal producer between the first and In Kenya, pyrethrum grows well in high altitude second world war (Purseglove, 1982). In the early areas between 1500 and 3000 m above sea level. 1920’s, it was planted in Switzerland and France. Fig. 1 shows the highlands between latitudes l”3O’N I? Wmdahwa et al./Industrial Crops and Products 5 (1996) 307-322 ’ WESTPOKOT f NANLX! 309 I’-MERU w : :’ I” rd’ NAROK \ l --- districtbolndory * moiortowns zyxwvutsrqponmlkjihgfedcb I I 0 25 I 50 1 xx) k m Fig. 1. Location of pyrethrum producing districts in West Kenya. and 2“s and longitudes 34”30’ and 38”30’E comprising sixteen administrative districts (approximately 97,300 km*) that grow pyrethrum. Here, lack of extreme climatic variation experienced in temperate regions results in longer periods (between 8 and 9 months) of flower flush and picking (Muturi et al., 1969). Regions that have annual rainfall between 1000 and 1400 mm are very suitable for cultivation. Amounts greater than 1400 mm increase root rot and bud disease incidence (Parlevliet, 1970). In the Kisii highlands (west of Narok and Kericho districts) where annual rainfall is more than 1600 mm, and in regions with less than 1000 mm (as in parts of Nyandarua district), pyrethrum grows relatively well. Rainfall in Kisii is well spread throughout the year, while the highlands of Nyandarua district experience misty conditions that reduce evapotranspiration. A dry period of at least 2 months rejuvenates plants. However, more than 4 months of dryness result in low yields (Acland, 1971). The optimum temperature for maximum photosynthesis lies between 15 and 20°C and chilling is required to initiate flowering (FAO, 1978). A temperature below 17°C for a period of six weeks is required to initiate flowering (Glover, 1955; Roes& 1976). Roest (1976) conducted experiments on the effect of nighttime, daytime and average temperature on the flowering of pyrethrum. He found that alternate low (under 13°C) nighttime and warm (15-20°C) daytime temperatures result in increased 310 Ff Wandahwa et al. /Industrial flower production. Average temperatures above 21°C inhibit flowering altogether. Temperature has a great effect on pyrethrins’ content of the flower as demonstrated by Kroll (1964) throughout Kenya. Regions with many cold misty and frosty months experience poor yields due to plant physiological damage, lack of warmth for vigorous growth and increased bud disease incidences. 3.2. Soil and landscape conditions Pyrethrum grows well on fertile, deep and well drained soils. Loamy soils derived from volcanic rocks that are found in the central highlands of Kenya are most suitable. They are capable of holding high amounts of water and have good soil structure that ensures good water infiltration. The crop stays in the field for 3 years. Within this period, there is repeated weeding and trampling of the soil. Unless the soil has good structure, it breaks down quickly followed by erosion (Acland, 197 1). Parts of Nyandarua and Narok districts are prone to waterlogging. It is recommended @roll, 1963) that the crop be planted on ridges because it does not tolerate waterlogged conditions. Ridging also creates better aeration and the soil may be subjected more intensely to the warming rays of the sun thus promoting growth in young plants. Mulching is recommended on soils that do not retain high amounts of water. Mulching in cold areas however, decreases yields in the first year probably due to cold top soil that causes poor development of young plants. It can grow on soils that are gravelly, slightly alkaline, slightly saline or calcareous @roll, 1963). Where these soils are present in Kenya, they would probably be excluded from cultivation on the basis of prevailing climatic conditions (Wandahwa and Van Ranst, 1996). Shallow soils (approximately 40 cm deep) found in the undulating to hilly landscape of Uasin Gishu district are utilized due to adequate rainfall (> 1000 mm) and the shallow rooting system of the crop. Most of the roots are found within the top 30 cm (Acland, 1971), while reported maximum rooting depth is 50 cm (Jaetzold and Schmidt, 1982/83). Experience in Kenya has shown that many smallscale farmers grow pyrethrum on land with a variety of physiographic units and at different slope levels. Crops and Products 5 (1996) 307-322 Suitable areas should be considered in terms of how slope affects soil erosion and land preparation methods. The crop gives little protection to the soil due to poor shading of the ground (Wielemaker and Boxem, 1982). This exposes the soil to direct rain drops and a variety of thriving weeds (Ngugi et al., 1989). Thriving weeds require frequent weeding that in turn causes soil pulverization and occasional trampling that reduces infiltration of water. Pyrethrum fields are therefore prone to soil erosion. Sloping land should be terraced or planted along contour lines. Regarding soil reaction, available information is not conclusive. Soil analysis from farmers’ fields and the Pyrethrum Board of Kenya nursery fields show that the crop grows on soils that greatly vary in their pH values. In Molo, a region that produces high yields, the soils range in pH from 4.4 to 6.3, while in Meru, a region with very low yields, soil pH range between 4.0 and 6.3 (Pyrethrum Board of Kenya, 1990a, 1991a,b). In India, it is reported to have been grown on soils with pH values between 3.0 and 5.1 (Raghavan Nair, 1955). Weiss (1966) reports soil acidity tolerance between pH values of 5.3 and 6.0, while Jaetzold and Schmidt (1982/83) report values between 5.6 and 7.5. The Pyrethrum Board of Kenya (1992) recommends soil pH values above 5.6. Perhaps the suitable soil pH should be evaluated in relation to how it affects availability of nutrients to the crop. Results of early experiments conducted by Kroll (1962, 1963) on the effect of calcium, magnesium, sulphur, molybdenum, zinc and copper on the production of pyrethrum were either not conclusive or showed that the crop does not respond to application of these elements. The Pyrethrum Board of Kenya (1992) recommends soils that have 2-10, l-3, 0.21.0, 0.2-2.0 and l-2 cmol(+) kg-’ soil of Ca, Mg, K, Na and Mn, respectively; 24% organic carbon; 0.2-0.4% available N and 2&80 ppm of available P. 4. Management 4.1. Field establishment Preparation of land to grow pyrethrum is aimed at eradicating perennial weeds. If the weeds are still in the field by the time the crop is planted, they can not be removed without destroying the crop (Acland, J? W andahwaet al. /Industrial Crops and Products5 (1996) 307- 322 1971). On large scale farms, primary tillage is done using a mouldboard plough or disc plough mounted on a tractor. Secondary tillage is done using disc harrows twice or more on virgin land and once on fallow land. On small scale farms, either a pair of oxen (draught animals) or a hand tool (hoe or forked jembe) is used. A pair of oxen requires ploughing and repeating till a fine tilth is obtained. A hoe is used to break the soil and a forked jembe used once to make tbe tilth smooth. Land preparation should be done when the soil is not too wet or too dry. The National Pyrethrum Research Station at Molo, a branch of the Pyrethrum Board of Kenya is responsible for producing planting material. Pyrethrum is planted from seeds as in varieties, or from splits as in clones. Research is aimed at producing varieties and clones that are high yielding in flowers and pyrethrins content, and which are resistant to diseases and pests. Clones are produced through recurrent selection from the population. Improvement is achieved by concentrating on favourable characteristics (genes or alleles). Varieties are produced through hybridization of two, three or more selected mother clones. Mother clones are multiplied through tissue culture. Farmers buy seeds from the Pyrethrum Board of Kenya office in Nakuru district, or purchase seedlings or splits from regional Pyrethrum Board of Kenya nurseries. Seeds are planted in raised seedbeds that measure 1.5 m wide and extend to any length. Phosphorus is applied prior to planting at the rate of 38 kg of P ha-’ and mixed with the top soil. Seeds are sown in furrows of 1.5 cm deep and 15 cm apart at a rate of approximately 100 seeds for 25 cm length. The seed-bed is covered by a thin layer of grass and water is applied. After 10 to 15 days, seeds germinate and the covering grass is reduced gradually to harden the shoots. Sometimes germination is quite poor due to the presence of unfertilized and non-viable seeds. Germinated seedlings are top dressed with 52 kg ha-’ of N. Fungi and thrips are prevented from attacking seedlings by spraying with 20 ml of Dithane M45 in 20 1 of water and 30 ml of Metasystox in 20 1 of water. Weeds are pulled out by hand. Four months after planting, seedlings are ready for transplanting. Multiplication of selected clones to produce splits is done in holes dug 15 cm deep at a spacing of 311 30 cm between rows and 15 cm within rows. Plants used for vegetative propagation are dug out using a forked jembe to avoid damaging the roots. Roots are trimmed to 10-15 cm long and flowering stems are cut off. The plants are divided into splits leaving a good proportion of the root system on each split. The number of splits produced per mother plant depends on the number of tillers the plant has (Kroll, 1948). Fungicides and nematicide are applied when necessary. The splits are planted vertically in the dug holes. Weeds are controlled by weeding regularly. Three to four months later the plants are ready to provide splits for distribution to farmers. Pyrethrum is transplanted at the beginning of the ‘long rains’ in March or April. Holes are dug 15 cm deep at a spacing of 60 cm between rows and 30 cm within rows and 38 kg ha-’ of phosphorus (basal P) applied. Roots and stems of splits or seedlings are trimmed and treated with fungicides and nematicide where necessary. They are planted vertically in the dug holes. The soil is put firmly around them. Between 5 and 10% of the plants may die. Gaping, a process of replacing the dead plants should be done without delay using large splits or seedlings in order to maintain proper plant population and allow re-fills to catch up with the rest of the plants. 4.2. Fertilizer application 4.2. I. and response Phosphorus first experiments conducted on pyrethrum in Kenya between 1945 and 1947 included the effect of mulch, lime and phosphates. As superphosphate was in rather short supply during the years immediately after the second world war, a mixture of 4.5 units of Uganda rock-phosphate and 1 unit of triple superphosphate was used. The results were rather disappointing. Only the water soluble superphosphate gave an immediate response, which in most cases was short-lived and sometimes resulted in diminished yields in the following years (Kroll, 1962, 1963). Application of lime produced no response in most cases, while mulch acted in different ways according to soil type, air temperature and rainfall at various altitude levels. Although these experiments were conducted over a fairly wide range of soils, it was considered desirable to increase the scale of subsequent trials. The 312 P: Wandahwa et al. /Industrial Work on phosphorus in particular was intensified from 1950 onwards. After a few seasons, it became obvious that the more leached red soils of high altitude areas (above 2400 m) gave remarkable yield responses when between 158 and 224 kg ha-’ of triple superphosphate (TSP, 43% PzOs) was applied. The phosphate was applied in the hole during planting and increased initial take, plant vigour as well as eventual flower yields @roll, 1962; Weiss, 1966). Top-dressing after planting or in the second or third season never had any effect. High TSP (448 kg ha-‘) application had no effect on flower yield whereas phosphorus application failed to increase the concentration of pyrethrins in the flowers (Kroll, 1962; Parlevliet et al., 1968). Reports on pyrethrum response to P application are conflicting. Studies in Kenya have shown positive yield responses @roll, 1962; Wanjala, 1991a), or no response at all (Mwakha, 1979). Similarly, 30% yield increase was obtained in Banglor (Rajeswara Rao et al., 1983) and Kodaikanal (Kumar et al., 1982), and no response in other experiments in India (Hussain and Ram, 1976; Rajeswara Rao and Singh, 1982). Ngugi and Ikahu (1989) showed that flower yield of clone 01641219 increased by 5% in two consecutive seasons when P was applied, whereas clone 4331 showed no response in either season. Clone 4331 did not respond to P application at Molo (Mwakha, 1979) and even produced 5% lower yield when P was increased from 97.5 to 195 kg ha-’ (Parlevliet et al., 1968). The trend reported in Kenya concerning the response of clone 4331 to P application is similar to that reported for clone CIG3 in Tasmania, Australia (Salardini et al., 1994a). Like in Kenya, P application in Tasmania failed to increase the concentration of pyrethrins in the flowers. In Kenya, the concentration of pyrethrins was influenced by clone differences, weather conditions and water supply (Wanjala, 1991a). The differences in response of pyrethrum to P could be explained by differences in uptake efficiency among clones and between young and established plants. In the preparation of splits, plants are divided into four or more splits, and roots and shoots are trimmed. At planting, active root volume is small, and plant vigour is significantly reduced by splitting and the shock of transplanting. At this Crops and Products 5 (1996) 307-322 stage, the splits need large supplies of P to fulfil their needs. In subsequent years, the roots of established plants may be able to obtain enough P from the soil. This, however, does not explain the reduction in yields which requires further investigation. Until more is known about the P nutrition of pyrethrum, it is recommended that, to minimize the risk of yield reduction, not more than 50 kg ha-’ of P and no sidedressed P should be applied (Salardini et al., 1994a). 4.2.2. Nitrogen Early experiments conducted in Kenya showed that N application to pyrethrum either had negative or no response (Collings-Wells, 1962; Kroll, 1953, 1962, 1963; Omerod, 1951). The significant response in the first and second seasons reported by Mwakha (1979) was a result of clone improvement. He observed that towards the end of the season, plants that did not receive N application had a characteristic yellowing of mature leaves and stalk terminals. In Kashmir India, N application increased tiller development and flower yields (Hussain and Ram, 1976). Ngugi and Ikahu (1989) observed differences in the way clones respond to N application. Clone 064/219 significantly increased in flower yields whereas clone 433 1 did not. Nitrogen application did not increase pyrethrins concentration in the flowers. Wanjala (1991a) recommends 52 kg ha-’ N top-dressed three months after transplanting in the first season, and repeated after cutting back in the following seasons (Pyrethrum Board of Kenya, 199Ob). 4.2.3. Potassium Information on yield response of pyrethrum to K application is limited. In Kenya, there has been no flower yield response to K application (Kroll, 1962, 1963; Parlevliet et al., 1968). In India, the response to K application has either been very small (under 5%) (Hussain and Ram, 1976; Rajeswara Rao et al., 1983) or absent (Rajeswara Rao and Singh, 1982). The amounts applied were approximately 110 kg ha-’ of K. Research in Tasmania has shown that pyrethrum (clone CIG3) requires about 40 kg ha-’ yr-’ of K, and does not respond to K applied on soils with more than 75 mg K per kg of soil (Salardini et al., 1994b). It is therefore recommended to apply 200 kg ha-’ of K at planting and 50 kg ha-i during zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 313 I! W andahwa et al. /Industrial Crops and Products 5 (1996) 307- 322 the following seasons on soils with less than 75 mg K kg-’ of soil. Most soils in Kenya have sufficient K and its application therefore may not be required. 4.3. Crop protection 4.3-l. Weed control Weeds found in pyrethrum fields vary from place to place. Those common to both low and high altitude areas include: Digitaria scalarurn chiov (Couch grass); Gulinsogu puruifloru Cav (Gallant soldier); Amaranthus hybridus L. (Pig weed); Tugetes minutu L. (Mexican marigold); Eleusine indicu L. (Wild finger millet); Bidens pilosu L. (Black jack); Duturu strumonium L. (Thorn apple); Cyperus rotundus L. (Nutgrass or Watergrass); Oxulis lutifoliu H.B.K. (Oxalis); Commelinu benghulensis L. (Wandering Jew); Portulucu oleruceu L. (Purslane) and Pennisetum clundestinum (Kikuyu grass). Those confined to high altitude areas include: Brussicu nupus L. (Rape); Stelluriu media L. (Chick weed); Spergulu urvensis L. (Spurrey); Gulium spurium L. (Cleavers or goose grass) and Chenopodium opulifolium (Round leaved goosefoot). The effective way to control weeds in pyrethrum fields is by hand weeding (Kroll, 1948; Mwakha, 1974; Ngugi et al., 1989; Wanjala, 1989). A small forked jembe that does not damage roots is used for weeding and putting the soil around the plants to encourage tillering (Acland, 1971). This should be done once every month (4 weeks) (Mwakha, 1974). Research on the use of herbicides is continuing and preliminary results indicate that herbicides are not effective against Digituriu sculurum, Cyperus rotundus, Commelinu benghalensis and Oxulis lutifoliu that have to be removed by hand (Ngugi et al., 1989; Wanjala, 1989). 4.3.2. Disease control True bud and false bud diseases affect pyrethrum. Although first reported in Kenya in 1946, available information on what really causes true bud disease is quite confusing. Reports (Nattrass, 1952, 1953, 1961 quoted by Robinson, 1963; Pyrethrum Board of Kenya, 1992) indicate that the disease is caused by fungi Rumuluriu bellunensis and Alternariu tenuis, a bacteria of Aschochytu spp. and a foliar nematode Aphelenchoides ritzemabosi (Schwartz) Steiner. Robinson (1963) refers to Alternuriu tenuis as a fungus of doubtful pathogenicity while Aschochytu spp. and Rumuluriu bellunensis are reported to cause Aschochyta disease and true bud disease, respectively. According to Bullock (1961), Aphelenchoides ritzemubosi is a leaf eelworm that causes leaf chlorosis and necrosis but which has little economic importance. The fungus R. bellunensis infects flower buds through the bracts and later invades the flower stalk. The buds start to dry and turn brown or purple-grey, the flower stalk withers as far as 2.5 cm below the bud and the dead bracts, florets and rays become confined to one side and looks like a ‘hanged man’ (Robinson, 1963). False bud disease is a physiological disorder that is associated with the genetic constitution of individual plants or clones and is caused by environmental conditions. Though it affects buds of all sizes, those between 1 and 2 mm diameter are most affected but can not be seen as they are hidden within the foliage. The small dead buds are termed ‘pin heads’. The characteristic symptom of false bud disease is the rapid death of several centimeters of stem below the dead bud followed by bending of the dead stem to produce a ‘shepherds’ crook’ (Robinson, 1963). Root rot or wilting disease is caused by fungi Fusurium gruminurium, Sclerotiniu minor (which occurs quite often), Sclerotiniu sclerotiorum and a nematode Prutylenchus spp (Pyrethrum Board of Kenya, 1992). Wounds caused through splitting and weeding, and the piercing of nematodes act as entry points for the fungi. The affected plants slowly wilt and die. In some cases partial recovery of the plant may occur. Root rot is local in distribution and is associated with poor soil drainage (Robinson, 1963), sites where huts were built and fertile forest soils (Acland, 1971). True bud disease and root rot are controlled through spraying with a fungicide Benlate at the rate of 0.5 kg ha-’ every two weeks. Preventive measures include: burning the cut plants at the end of the season, planting disease free material dipped in fungicides to protect wounds caused by splitting, applying nematicide in areas where nematodes are prevalent and practising crop rotation to keep down disease incidence. A more practical solution is to breed disease-resistant varieties. 314 I? Wmdahwa et al. /Industrial Cnops and Products 5 (1996) 307-322 rate of 2.0-4.0 g per plant and 0.5 g per plant, re4.3.3. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Pest control spectively. These applications will control any other In Kenya, two different types of thrips are known soil insects (Cutworms, Diptera and Coleoptera larto cause economic problems at different levels of vae) that may pose hazards to the plants. Prevenproduction in the pyrethrum industry. Thrips nigmpitive measures include: planting disease free material, Zosus Uzel (leaf thrips) poses problems to pyrethrin breeding resistant varieties and use of a cereal (e.g., production. Thrips tubaci Lind (flower thrips) affects wheat) in the rotation. Wheat is a poor host of root seed production. Both differ in their predatory habits. knot nematodes (Johnson, 1985). Thrips nigropilosus Uzel which was first discovered in Kenya in 1957 scrapes the leaf epidermis, thus reducing chlorophyll content, and feeds on the cell 4.4. Flower harvesting and handling contents. This causes leaf desiccation and foliar damIn Kenya, pyrethrum produces flowers continuage that appear as silvery patches and later become ously for a period of eight to nine months. Therefore necrotic. The nymphs spend the first and second harvesting is done by hand. During this period, all stages of their lives on leaves while the third and stages of flower development are present. Eight disfinal stages are spend in the soil. Thrips tubuci Lind, tinct stages of development are shown in Table 1 first recorded in Kenya in 1937, lives exclusively in the flower where it attacks petals and florets making (Head, 1966). The concentration of pyrethrins in the ‘flower’ increases from bud (stage 1) to a maximum them brown (Bullock, 1961). when 3 to 4 rows of ray florets are open (between Few thrips can be tolerated by the pyrethrum plant stage 4 and 5), and then reduces gradually as the before significant yield losses (in relation to costs of florets mature. The dry weight of the flower head incontrol) occur. As the loss can be very large (43% ) in creases from bud stage to reach maximum at the late the dry season, farmers are advised to spray as soon overblown stage 7. Research in harvesting pyrethrum as the leaf thrip is present on the foliage (Smith and flowers focuses on high yield of pyrethrins content Hanson, 1991). Spraying with Roger (dimethoate (w/w) (Bhat and Menary, 1984; Head, 1963, 1966; 40%) at the rate of 0.5 1in 400 1 of water will control Kroll, 1948; Parlevliet, 1970). Most clones have high the d-nips. Preventive measures include removal of pyrethrins’ content between stages 5 and 7 (Ikahu weeds like Galinsoga parvijlora and Bidens pilosa and Ngugi, 1989). that are alternative hosts of leaf thrips. The first harvest should take place when the first The Red spider mite (Tetrany chus M eni) is a pest flowers have all disc florets open (stage 5), approxof economic importance in areas with a marked dry imately 21 days after the buds are fully developed. season. Its numbers have been known to increase Subsequent harvests should be done every two weeks when DDT or dieldrin is used against thrips (Acland, (14 days) and should include all flowers in stage 5 1971). In Kenya, the pest is found in all pyrethrum and above. In this way, flowers previously in stage growing areas and can be controlled by spraying di2, 3 and 4 are harvested while still having high methoate 40% and thioden 35% at the rate of 11 ha-‘. pyrethrins’ content. Precautions should be taken not Earlier reports (Bullock, 1961; Robinson, 1963) to pick flowers when they are wet and not to include indicated that pyrethrum was either tolerant to root part of the flower stalk among the flower heads as knot nematodes (M eloidogy ne hapla, Chitwood) or they reduce the pyrethrins’ content. that the effects of the species did not appear damAfter harvesting, flowers should be dried immeaging to the plants. It was later found however, that diately to avoid fermentation and loss of pyrethrins. the nematodes can be quite a menace during a dry Drying using machines has been tried in Kenya season (Acland, 1971). They attack pyrethrum roots (Acland, 1971; Mumo, 1961) but has not been and form knots. The plants appear healthy during very successful (Pyrethrum Board of Kenya, 1992). the rainy season producing flowers as usual but show Therefore farmers dry their flowers in the sun on symptoms of attack during a dry season. wire mesh trays raised 0.6 to 1 m above the ground. Furadan (Carbofuran) at the rate of 1 g per planting hole should be applied during planting. Mocap Flowers are spread in a thin layer (about 4 cm) to allow air circulation and stirred at least 3 times a day. 10G and Nemacur can be sprayed in the fields at the I! W mdahwa ei al. /Industrial Crops and Products 5 (1996) 307- 322 315 Table 1 Flower development stages and number of days to each stage (source: Head, 1966) Stage of development Description Approximate time for development (days) 1 2 3 4 5 6 Well developed closed buds Ray florets vertical Ray florets horizontal, first row of florets open Approximately 3 rows of disc florets open All disc florets open, and fully mature Early overblown condition, disc florets’ color diminishing but ray florets still intact Late overblown condition, little color remaining in ray florets but still intact, ray florets dried out Disc florets fallen, stems dry a centimeter below the head, suitable for seed collection 0 12 16 19 21 7 8 At night or during the rain, they are covered or put indoors. They are dry (lO-12% w/w moisture) when 4 out 5 flower heads smash easily when squeezed between thumb and fore-finger. Dry flowers are packed in sisal bags to about 30 kg that are well labelled for transportation to the factory. Dried flowers are sold to the Pyrethrum Board of Kenya in Nakuru where processing takes place. The Board has a network of buying centers within the growing regions. The centers consist of cooperative unions with 100 or more members receiving flowers from smaller societies to deliver to the factory, associations of 20 to 30 members that deliver their flowers as a group, or individual farmers who deliver themselves to the factory or through the pyrethrum field officers. Payments are delivered to the cooperatives, associations, field officers or to the individual farmer. 31 43 60 While utilizing information from the District Annual Reports of the Ministry of Agriculture (19871991), the Pyrethrum Board of Kenya papers, and the agronomy section of Pyrethrum Board of Kenya, an attempt was made to calculate the average district dried flower yields of the farmers (Table 2). There was a steady increase in yields from 1987 to 1991, probably due to improving management practices. Despite the variations, yields show a general decreasing trend from Nakuru to Embu district. Matching Tables 3 and 4 adapted to climatic and soil conditions with the respective climate and soil conditions where pyrethrum is grown (Table 5) in West Kenya, revealed that Embu and Murang’a districts are less favourable for pyrethrum cultivation. As a result, average annual yields are low. In 1960, the average annual yield was about 440 kg ha-’ yr-’ of dried flowers. This amount fell as the growing of flowers changed hands from experienced large-scale 5. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Management constraints farmers to inexperienced small-scale holders and spread from more favourable areas in Nakuru district 5.1. L49wjoweryielak zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA to less favourable areas in Murang’a and Embu districts. By the end of 1960s the average had fallen to Farmers’ yields are not well documented. To280 kg ha-’ yr-’ (Acland, 1971). In 1960, farmers tal production of dried flowers is recorded by the practising good crop husbandry obtained about 1350 Pyrethrum Board of Kenya (PBK) which buys all the flowers. The land area under production is not kg ha-’ yr-’ of dried flowers. Similar yields are still realized today under experimental conditions, well documented as some farmers are not registered and sell their flowers through registered ones. Flower with those common between 1500 and 2000 kg ha-’ delivery increased from 7537.8 tonnes in 1988/89 yr-‘. Yields above 2500 kg ha-’ yr-’ are rare and season to 9640.6 tonnes in half of 1992193 seahave been reported (Ngugi and Ikahu, 1989) at Molo Research Station for clone 4331, the highest being son. The Ministry of Agriculture reports dried flower yields and attempts to estimate the land area under 4681.8 kg ha-’ yr-’ with 1.5% (w/w) pyrethrins’ content. There is need to restrict cultivation to areas production using their extension service officers. 316 F! Wandahwa et al./Industrial Crups and Products 5 (19%) 307-322 Table 2 District pyrethrum yields (kg ha-‘) from 1987 to 1991 in 15 districts in West Kenya District NaklUll Kericho Uasin Gishu Baringo Nyandarua Marakwet Narok West Pokot Kiambu Laikipia Nyeri Nandi Meru Murang’a Embu Average Year Average CV a (%) 1987 1988 1989 1990 1991 740 308 399 278 334 185 184 160 396 152 240 117 239 80 272 689 391 436 244 373 181 152 210 316 107 200 507 457 520 242 352 178 256 300 250 293 253 248 38 22 280 541 644 605 665 283 593 547 360 252 542 237 333 238 60 421 663 715 496 624 423 516 489 467 255 354 256 400 242 36 424 287 18 277 628 503 491 411 353 331 326 299 294 290 237 283 251 59 34 319 15.9 34.1 16.2 52.2 14.6 62.4 55.4 40.6 21.6 59.9 52.3 8.1 9.3 51.2 56.1 - a CV, coefficient of variation. Table 3 Climatic requirements for pyrethrum cultivation Climatic characteristics Decreasing favourable conditions from 1 (very good) to 5 (unsuitable) 1 2 3 4 5 Mean annual rainfall (mm) a 1100-1200 LDS b (months) l-2 <ll 15-20 12-15 - 1200-1400 1000-1100 3 <l 11-13 20-22.5 13-15 15-17 10-12 1400-1600 95&1000 4-6 - >I600 900-950 7 C900 >7 13-15 22.5-25 cl3 17-19 7-10 15-17 >25 >17 19-21 <7 r21 Mean nighttime temperature’ (“c) Mean daytime temperature d (“c) Average daily temperature e (“c) BIncreasing rainfall increases disease incidence while less is inadequate. b Length of a dry season of 1 or 2 months rejuvenates plants, continuous rams are not very favourable and the crop fails in areas with more than 7 months of dryness. c Lower temperatures encourage bud formation. d Temperatures affect flower development. e Temperatures used in absence of nighttime or daytime temperatures. with favourable climate where great potential to increase yields obtained by farmers and those obtained under research conditions exists. pyrethrins are refined and put into containers for export. More than 95% of the pyrethrins are exported, the rest is utilized locally to make insecticides. From what is exported, 65% is sold to the USA. The rest is sold to Europe, Asia, South America, the Caribbean, 5.2. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Fluctuating world market and producer prices Middle East and some African countries. Pyrethrins are extracted from flowers at the Unlike tea and coffee, the world market price Pyrethrum Board factory in Nakuru. Extracted for pyrethrum is not determined in auctions and is F! Wana’ahwa et al./Industrial Crops and Products 5 (19%) 307-322 317 Table 4 Soil and landform requirements for pyrethrum cultivation Land-use requirements/ characteristics Decreasing favourable conditions from 1 (very good) to 5 (unsuitable) 1 2 3 4 5 <8 cl6 <25 <30 >30 FO WD SED ED Fl MD F2,F3 I,P,VP C<6Os to L <5 >90 t12 C>6Os, SCL 5-15 12-24 SL, C<6Ov 15-35 60-40 24-35 C>6Ov, LfS, LS 35-55 40-20 35-50 SiCm, Cm, S, fS, CS >55 (20 250 Apparent CEC (cmol (+) kg-’ clay) Sum of basic cations (cmol (+) kg-’ soil) pH water (1: 2.5) >24 >3.2 6.0-5.6 6.0-6.4 24-16 3.2-2.4 5.6-5.2 6.4-6.8 <16 (-) 2.4-1.6 5.2-4.8 6.8-7.5 <16 (+) <1.6 14.8 >7.5 Organic carbon (%) >2.4 2.4-1.5 1.5-0.8 to.8 c2.0 ~6.0 2.0-4.0 6.0-10 4.0-8.0 10-15 8-15 15-40 Erosion hazard s1ope.a (%) Wetness b Flooding c Drainage d Rooting conditions Texture and structure e Coarse fragments (%) Soil depth (cm) CaCOs (%) Fertilig status Salinity and alkalinity hazard ECe f (dS/m) ESPs (%) 215 >40 a Increasing slope increases erosion hazard. b Water logging is not tolerated. ’ FO, Fl , F2, and F3 indicate none, occasional, seasonal and permanent excess surface water, respectively. d VP, very poorly drained; P, poorly drained; I, imperfectly drained; MD, moderately drained, ED, excessively drained, SED, somewhat excessively drained; WD well drained. eCm, massive clay; SiCm, massive silty clay; CAOv, fine clay, vertical structure; CAOs, fine clay, blocky structure; C<6Ov, clay, vertical structure; 0s to L refers to: clay, blocky structure; silty clay, blocky structure; silty clay loam; clay loam; silt loam; sandy clay; and loam; SCL, sandy clay loam; SL, sandy loam; LfS, loamy fine sand; LS, loamy sand, S, sand; fS, fine sand; cS, coarse sand. f ECe, electrical conductivity of the saturation extract. s ESP, exchangeable sodium percentage. less transparent. Negotiations with known customers of the Pyrethrum Board are done through telephone or telex. Competition from cheap synthetic products affect both the world market and producer prices. In 1982/83 season, total flower production was about 19,000 tonnes. By the end of 1983, there was a stock pile of 19,000 tonnes of pyrethrins’ extract in Kenya due to poor world market prices. Farmers were not paid in time for the flowers they delivered to the factory, the delay lasting for more than 18 months in some cases. Most farmers uprooted the crop and annual production fell to about 3000 tonnes of dried flowers in 1983/84, 1984/85 and 1985/86 seasons. Improvement of world market prices in 1987 and depreciation of the Kenya shilling in 1989 led to increased producer prices (Table 6). By 1990/91 season, annual production had increased to 10,000 tonnes of dried flowers (Ministry of Agriculture, 1992). Producer prices are worked out by the Pyrethrum Board using information generated from monthly flower deliveries, annual production estimates, world market price indications and trends. Using a trading account through costing of processing, transport, personnel, chemicals, etc. an interim (before end of financial year) price is worked out on the basis of pyrethrins’ concentrations in the flowers. In 1990/91 season, interim producer price was Ksh 2500 kg-’ pyrethrins (US$ 1 = Ksh 30.026, 31 March 1991). One tonne of dried flowers containing 318 I? Wandahwa et al. /Industrial Crops and Products 5 (19%) 307-322 Table 5 Dominant soil units and climatic conditions where pyrethrumis grown in 15 districts in West Kenya District Soil units (FAO-UNESCO, 1974) N~~uN mollic Andosols ando-luvic Phaeozems mollic Nitisols ando-luvic Phaeozems humic Nitisols nito-chromic Luvisols nito-chromic Luvisols ando-luvic Phaeozems trim-chromicLuvisols humic Nitisols ando-luvic Phaeozems mollic Nitisols humic Cambisols humic Nitisols n&o-chromicLuvisols hmnic Nitisols humic Nitisols humic Nitisols humic Nitisols humic Nitisols Kericho Uasin Gishu Baring0 Nyandarua Keiyo Marakwet Narok West Pokot Kiambu Laikipia Nandi Meru Nyeri Murang’a Embu MABa (mm) 950-1400 1200-1400 1100-1400 12c0-1400 MANTb (“c) MADT c (“C) LDS d (months) tll-15 15-20 l-6 15-20 15-20 15-20 l-4 l-4 14 15-20 26 15-20 3-t 15-25 15-20 15-20 15-22.5 15-22.5 20-25 15-22.5 15-22.5 20-25 1-3 3-4 4-6 4-6 l-3 4-6 4-6 4-6 4-6 11-15 11-13 11-13 looo-1400 <ll-13 1109-1200 11-15 llcO-1600 1100-1200 100&14QO 950-loo0 1200-1400 950-1400 950-1400 950-1400 900-1100 tll-17 13-15 11-15 13-15 13-15 13-17 13-17 15-17 15-17 a Mean annual rainfall. b Mean annual nighttime temperature(“C). c Mean annual daytime temperature(“C). d Length of a dry season, defined as number of months rainfall is less than half of evapotranspiration. 1.0% of pyrethrins concentration was Ksh 25,000, while that containing 1.2% was Ksh 30,000. Interim payments are made every month for flowers delivered the previous month. At the end of the season, a pool price is worked out and final payments are made. The final payment is referred to as ‘bonus’. Better producer prices and increased flower production will lead to high income that can sustain a farmer throughout the year just like formal employment. 5.3. Research, finding and dissemination of information Agronomic research is done by the National Pyrethrum and Horticulture Research Station (NPHRS) at Molo, a branch of Kenya Agricultural Research Institute (KARI) and the agronomy section of the Pyrethrum Board of Kenya (PBK). Breeding is exclusively done by the NPHRS. Table 7 shows a list of clones and varieties recommended by the NPHRS. Besides these, farmers grow a number of local clones especially in Kisii (west of Narok and Kericho districts). Among them are Kenya, K7, Maranga, Gekoma, Nyamasibi, Nyankoba, C47, Ebiosi and Congo (Wanjala, 1991b). These clones are numerous and proper research cannot be done on all of them given the limited funds. Besides, there is lack of coordination in research between the PBK and KARL Each researcher deals with the clones he likes and lays down the experiment on the soil and environment he likes. The results are inconsistent and difficult to use. Fertilizer trials are the dose-response type in which the fate of fertilizer nutrients applied is not part of the investigation. Measurements of nutrient contents in the various crop parts and in the soil are not done. Published nutrient concentration values in harvested product and crop residue are too general and not clone specific (Smaling et al., 1993). It is therefore difficult to establish the crucial relations between nutrient application and nutrient uptake and that between nutrient uptake and yield. No information is available on the fraction of the inorganic f? W undahwa et al. /Industrial Crops and Products 5 (19% ) 307- 322 Table 6 Pyrethrum producer prices in Kenya and percent increase over the previous year from 1975 to 1990 (Source: Ministry of Agriculture, 1992) Year Price (Ksh a kg-’ pyrethrins) 1975/76 1976/77 1977t78 19780’9 1979180 1980/8 1 1981/82 1982/83 1983/84 1984/85 1985/86 1986187 1987188 1988/89 1989190 392 430 516 670 1000 1150 1150 1150 1150 1150 1250 1304 1650 2030 2615 Increase (%) Table 7 Recommended clones and varieties in Kenya, year of release, pyrethrin concentration and altitude above which they should be grown (Source: Pyrethrum Board of Kenya, 1990a; Pyrethrum Board of Kenya, 1992) Clones/varieties 9.7 20.0 29.8 49.8 15.0 0.0 0.0 0.0 0.0 8.7 4.3 26.5 23.0 28.8 a30.026 Kenya shillings = LJS$ 1 on 31 March 1991. nutrients applied that is taken up by the plant (recovery fraction) on different soils and environments in Kenya. No information is available on nutrient utilization efficiency by different clones for production of biomass with an economic value, There is need for research that will provide this information. Pyrethrum continues to gain interest as a new industrial crop among small scale farmers who would like to grow it. Crop yield simulation models are an important land evaluation tool used in making decisions on whether to or not to introduce new crops into existing agricultural systems. Such quantitative models require specific crop parameters not available in the case of pyrethrum. So far, only a qualitative (descriptive in nature) land use assessment model in which the concept of land use and the associated crop requirements are formulated against a socio-economic background has been demonstrated (Wandahwa and Van Ranst, 1996). Model-oriented research on crop phenology, light interception, light use efficiency, biomass growth and partitioning and water use efficiency is required in order to shorten the duration and lower the costs of experiments in potential yield exploration when introducing pyrethrum among existing agricultural systems. 319 Clones 4331 Sbl661107 Ma/700013 KG’0164 Ma/71/423 Kst751313 Kst7U43 L/72/26 Krl741443 Km41223 Km4tl22 MoL’Olll24 Year of release Pyrethrins concentration (%) Altitude (m) 1964 1976 1979 1979 1979 1979 1980 1980 1982 1982 1982 1979 1.6 2.0 1.9 1.9 1.8 1.6 2.1 2.1 2.1 1.95 2.1 1.9 1800 2200 2200 1700 2200 1700 1700 2200 1700 1700 1700 2200 1970 1988 1988 2.0 2.1 1.9 2100 1700 1700 Varieties P4 K218 K235 Research work should also cover mechanical harvesting and drying which will reduce the high labour demand of the crop. The present clones which flower continuously for 8 to 9 months are difficult to harvest with machines without spoiling the crop. There is need for a decision on whether clones that produce flowers at once and which are therefore easy to mechanize should be developed (like in Tasmania) or whether those that flower for a long period and require manual labour should be retained. Research on high yielding and disease resistant varieties, pesticides and herbicides’ application should be intensified. The problem of clones with high dried flower yields having low pyrethrins’ concentration should be investigated and solved through genetic engineering. Research funds are limited. The PBK allocates Ksh 400,000 to research annually. This amount is too limited and should be increased. However, farmers will only accept research funds to be increased if recommendations out of research findings are useful to them. Research information is disseminated through an exclusive journal, ‘The Pyrethrum Post’ published since 1948, and other publications of the 320 I! Wandahwa et al./Industrial Crops and Products 5 (1996) 307-322 agronomy section of PBK. Once research in agronomy is improved, the quality of information reported in these publications will also improve. 5.4. Credit and extension services Farmers need credit to manage the high operational costs at the start of the first season. When harvesting starts, they should be able to sustain production costs since they are paid every month for flowers delivered the previous month. The credit scheme currently operated by PBK does not cover everybody. It is given as farm inputs and lowers the farmers’ costs of production. For example in 1991/92 season, a 50 kg bag of triple superphosphate (TSP) was supplied to farmers in Kisii district at a cost of Ksh 415 instead of the commercial price of Ksh 426. Credit facilities are also provided for transportation of planting material to tbe farmer and dried flowers to the factory. There exists conflict between the PBK extension officers and those of the ministry of agriculture. Farmers are in the process left without the necessary advice. Frequent field days and seminars should be organized in order to reach farmers. Extension service officers of the PBK need regular in-service courses to upgrade their knowledge on research information, data collection and record keeping. Pyrethrum is one of the crops with high labour requirements. Farmers should be well advised before engaging in production. 6. Conclusions There was a steady increase in flower yields in West Kenya from 1987 to 1991, probably due to improving management practices resulting from increasing producer prices. Growing pyrethrum in less favourable climatic conditions results in low yields. There is need to restrict cultivation to areas with a favourable climate where potential to increase yields through good crop husbandry and better credit facilities exist. Natural pyrethrum products face competition from cheap synthetic ones, despite their being harmful to mammals. Strong campaigns against the harmful cheap synthetic products and better marketing strategies for pyrethrum could increase use and thus demand for safe pyrethrum products. Research on high yielding varieties (high dry flower weight and pyrethrins concentration) that are resistant to diseases and pests and have low labour demands, is necessary for the pyrethrum industry in Kenya to succeed. References Acland, J.D., 1971. East African crops. An introduction to the production of field and plantation crops in Kenya, Tanzania and Uganda. Longman/FAO, Rome. Bhat, B.K. and Menary, R.C., 1984. Genotypic and phenotypic variation of floral development of different clones of pyrethrum Chrysanthemum cinerariaefolium Vis. Pyrethrum Post, 15(4): 99-104. Bullock, J.A., 1961. The pests of pyrethrum in Kenya. Pyrethrum Post, 6(2): 22-24. Chandler, ES., 1951. Botanical aspects of pyrethrum. General considerations: the seat of the active principles. Pyrethrum Post, 2(3): l-8. CIG Pyrethrum, 1995. PYLINES, No. 4. Collings-Wells, L.J., 1962. Annual report. Senior pyrethrum officer, Ministry of Agriculture, Nairobi. Elliot, M., Kimmel, E.C. and Casida, J.E., 1969. 3H-Pyrethrin I and -Pyrethrin II: preparation and use in metabolism studies. Pyrethrum Post, lO(2): 3-8. FAO, 1978. Report on the agro-ecological zones project, Vol I: Methodology and results for Africa. World soil resources Rep. No. 48/l, FAO, Rome. FAO-UNESCO, 1974. Soil Map of the World, 1.5,000,000, Vol I Legend. UNESCO, Paris. Glover, J., 1955. Chilling and flower bud stimulation in pyrethrum (Chrysanthemum cinerarieafolium). Ann. Bot. (London), 19: 138-148. Head, S.W., 1963. An examination of the effect of picking methods on the pyrethrins content of dry pyrethrum flowers. Pyrethrum Post, 7(2): 3-9. Head, S.W., 1966. A study of the insecticidal constituents in Chrysanthemum cinerariaefolium: (1) their development in the flower head; (2) their distribution in the plant. Pyrethrum Post, 8(4): 32-72. Head, S.W., 1969. The composition of pyrethrum extract. Pyrethrum Post, lO(2): 17-21. Hussain, T. and Ram, I!, 1976. Effect of NPK on tillering, flower bud formation, and fresh flower yield of pyrethrum crop. Pyrethrum Post, 13(3): 89-90. Ikabu, J.M. and Ngugi, C.W., 1989. Investigations into yield losses of some pyrethrum clones through picking of flowers at improper stage of development. Pyrethrum Post, 17(2): 56-59. Jaetzold, R. and Schmidt, H., 1982/83. Farm Management Handbook of Kenya. Vol. II, Parts A, B and C. Ministry of Agriculture, Nairobi. Johnson, A.W.. 1985. Specific crop rotation effects combined with cultural practices and nematicide, in Sasser, J.N. and Carter, C.C. (Editors): Advanced Treatise on Meloidogyne. Vol. I, Biology and Control, North Carolina State Graphics, NC. F! Wandahwa et al. /Industrial Crops and Products 5 (1996) 307-322 Kayongo-Male, H. and Abate, A., 1989. The role of pyrethrum (Chrysanthemum cinerariaefolium) Marc in livestock nutrition - a review. Inter Afr. Bur. Anim. Resour., 37(4): 385-390. Kroll, U., 1948. Pyrethrum and good farming. Pyrethrum Post, l(2): 23-27. Kroll, U., 1953. Annual report. Agricultural officer (pyrethrum), Ministry of Agriculture, Nairobi. Kroll, U., 1962. The improvement of pyrethrum yields through the application of fertilizers. Pyrethrum Post, 6(3): 32-33. Kroll, U., 1963. The effect of fertilizers, manures, irrigation and ridging on the yield of pyrethrum. East Afr. Agric. For. J., 28: 139-145. Kroll, U., 1964. Effects of mean temperature on the content of pyrethrins in the flowers of Chrysanthemum (pyrethrum) cinerarieafolium. Nature, 202: 1351-1352. Kumar, N., Arumugam, R. and Kanasamy, O.S., 1982. The effect of NPK on flower production of pyrethrum (Chrysanthemum cinerariaefolium Vis.). South Indian Hortic., 30: 99-103. Mathur, A.C., Srivastava, J.B. and Chopra, I.C., 1961. A note on the toxicological investigations of pyrethrum Marc. Pyrethrum Post, 6(l): 11 Ministry of Agriculture, 1987-1991. District Annual Reports. Ministry of Agriculture, Nairobi. Ministry of Agriculture, 1992. Pyrethrum Production and Marketing in Kenya, Current Situation and Outlook. Ministry of Agriculture, Development Planning Division, Nairobi. Munro, R.J., 1961. An experiment on the drying of pyrethrum flowers. Pyrethrum Post, 6(2): 25-29. Muturi, S.N., Parlevlief J.E. and Brewer, J.G., 1969. Ecological requirements of pyrethrum. I: A general review. Pyrethrum Post, 10(l): 24-28. Mwakha, E., 1974. Effect of weeding frequency on establishment of pyrethrum in Kenya. Pyrethrum Post, 12(3): 98-102. Mwakha, E., 1979. Investigations of factors related to pyrethrum response to nitrogenous fertilizer: III phosphate fertilizer. Pyrethrum Post, 15(2): 44-47. Nattrass, R.M., 1952. Annual Report. Department of Agriculture., Kenya. Nattrass, R.M., 1953. Annual Report. Departmen. of Agriculture, Kenya. Nattrass, R.M., 1961. Host lists of Kenya fungi and bacteria. Mycological papers, No.18, Commonwealth Mycological Institute. Ngugi, C.W. and Ikahu, J.M., 1989. The response of pyrethrum (Chrysanthemum cinerariaefolium Vis.) to phosphorus and nitrogen fertilizers. Pyrethrum Post, 17(2): 70-73. Ngugi, C.W., Ikahu, J.M. and Gichuru, S.P., 1989. The effect of Venzar in weed control in established pyrethrum fields. Pyrethrum Post, 17(2): 52-55. Omerod, EH., 1951. Annual Report. Ministry of Agriculture, Nairobi. Parlevliet, J.E., Muturi, S.N. and Brewer, J.G., 1968. Influence of spacing and fertilizer on flower yield and pyrethrins content of pyrethrum. Pyrethrum Post, 9(4): 28-30. Parlevliet, J.E., 1970. The effects of rainfall and altitude on the yield of pyrethrins from pyrethrum flowers in Kenya. Pyrethrum Post, lO(3): 20-25. 321 Purseglove, J.W., 1982. Tropical crops. Dicotyledons. Longman, New York. Pyrethrum Board of Kenya, 1990a. Molo Soil Sampling and Analysis. Scientific Research and Agronomic Services Department, Pyrethrum Board of Kenya, Nakuru. Pyrethrum Board of Kenya, 199Ob. Pyrethrum Growers Manual. Pyrethrum Board of Kenya, Nakuru. Pyrethrum Board of Kenya, 1991a. Soil Sampling and Analysis for Meru District. Scientific Research and Agronomic Services Department, Pyrethrum Board of Kenya, Nakuru. Pyrethrum Board of Kenya, 1991b. 01 Joro Grok Soil Sampling and Analysis. Scientific Research and Agronomic Services Department, Pyrethrum Board of Kenya, Nakuru. Pyrethrum Board of Kenya, 1992. Recommendations Arising from Agronomic Research and Other Sources in Kenya. Pyrethrum Growers Handbook, Pyrethrum Board of Kenya, Nakuru. Raghavan Nair, K.N., 1955. World Crops, 7(7): 274. Rajeswara Rao, B.R. and Singh, S.P., 1982. Effect of fertilization on the flower yield and pyrethrins content in pyrethrum. Proceedings of National Seminar on Medical and Aromatic Plants, Coimbatore, pp 4-6. Rajeswara Rao, B.R., Singh, S.P and Rao, E.V.S.P., 1983. N, P and K fertilizer studies on pyrethrum (Chrysanthemum cinerariaefolium). J. Agric. Sci., Cambridge, 10: 509-511. Robinson, R.A., 1963. Diseases of pyrethrum in Kenya. Est. Afr. Agric. For. J., 28: 164-167. Roest, S., 1976. Flowering and Vegetative Propagation of Pyrethrum (Chrysanthemum cinerarieafolium Vis) in Vivo and in Vitro. PbD Thesis, Pudoc, Wageningen. Salardini, A.A., Chapman, K.S.R. and Hollway, R.J., 1994a. Effect of basal and side-dressed phosphorus on the achene yield and pyrethrins concentration in the achenes of pyrethrum (Z’bnacetumcinerariifolium) and on soil and plant phosphorus. Aust. J. Agric. Res., 45: 231-241. Salardini, A.A., Chapman, K.S.R. and Hollway, R.J., 1994b. Effect of potassium fertilization of pyrethrum (Tanacerum cinerariifolium) on yield, pyrethrins concentration in dry achenes and potassium concentration in soil and plant tissues. Aust. J. Agric. Res., 45: 647-656. Smaling, E.M.A., Stoorvogel, J.J. and Windmeijer, P.N., 1993. Calculating soil nutrient balances in Africa at different scales, II. District scale. Fert. Res., 35: 237-250. Smith, L.M. and Hanson, P.M., 1991. Yield reduction in pyrethrum caused by Thrips nigropilosus Uzel. (Thysanoptera: Thripidae). Trop. Agric. (Trinidad), 68(3): 235-238. Wandahwa, P. and Van Ranst, E., 1996. Qualitative land suitability assessment for pyrethrum cultivation in west Kenya based upon computer-captured expert knowledge and GIS. Agric. Ecosyst. Environ., 56: 187-202. Wanjala, B.W.K., 1989. Evaluation of promising herbicides for control of weeds in pyrethrum fields in Kenya. Pyrethrum Post, 17(2): 60-65. Wanjala, B.W.K., 1991a. Influence of farm-yard manure, phosphatic and nitrogenous fertilizers on pyrethrum production in Kenya. Pyrethrum Post, 18(2): 55-60. Wanjala, B.W.K., 1991b. Performance of low-altitude unim- 322 I? Wanhhwa et al. /Industrial Crops and Products 5 (1996) 307-322 proved pyrethrum clones grown in Kisii, Kenya. Pyrethrum Post, 18(2): 61-64. Weiss, E.A., 1966. Phosphate-lime trials on pyrethrum. Pyrethrum Post, 8(3): 19-21. Wielemaker, W.G. and Boxem, H.W., 1982. Soils of the Kisii area. Reconnaissance Soil Survey Rep. No. R4, Kenya Soil Survey, Nairobi.