Fertilisation pest and insect control

Beside the soil preparation (ploughing), oregano cultivation demands fertilisation with ammonium phosphate during November to December, and efficient pest control (weeding out) (Sarlis, 1994).

Fortunately, the savoury herbs are not especially subject to serious damage by disease or insect pests, particularly when grown on a small scale. This may be due in part at least to the repellent or inhibitory action of their aromatic oils. When they are grown on a commercial scale, however, certain diseases and insect pests do cause damage under some conditions. In unusually dry weather the red spider mite may cause some damage to oregano by developing brown leaf spots, but since these diseases and insects are of infrequent occurrence and seldom cause serious damage the grower need not be greatly concerned about them. The aphids can be controlled easily with commercial dusts or spray solutions containing nicotine, rotenone, or pyrethrum. The red spider mite and the fungus diseases are more difficult to control, but they present no problem under normal conditions.

Oregano attracts honeybees, which pollinate other flowering plants. With its low compact growth, oregano makes a good border plant. Once in bloom, the plants may produce flowers throughout the growing season. Plants should be pinched back to encourage bushier growth.

Comparative methods of oregano cultivation

In central European countries, especially in Hungary, the cultivation of O. majorana has a long tradition. Commercial material of oregano (O. vulgare) is partially collected from wild plants even today. To avoid the disadvantages of exploiting oregano directly from the wild, efforts have been made in the area of its domestication and cultivation. The selection of new cultivars is underway and the material already selected is characterised by 0.5—1.5 per cent oil content containing carvacrol and thymol as the main compounds (Bernath, 1996). In Hungary, oregano is cultivated on light, dry and well-drained soils, which are somewhat alkaline. Propagation can be done vegetatively by separation of roots or by seed. Roots are planted in the field in September—October. The seed should be sown in an open-air nursery with inter-row distances of 25 cm in April. One gram of seed is usually sufficient for sowing 1 m2 of nursery. The depth of sowing is 5—10 mm. Seedlings can be transplanted to the field in May, when they reach 10—12 cm in height. They are planted with a spacing of 50—60 cm between rows and 20—25 cm within rows. Irrigation is required at the time of planting and a few other times in the first year. In the following years, plants have developed an efficient root system and thus no further irrigation is usually needed. Plants are harvested at blooming stage and dried afterwards in shade or by artificial means to preserve the colour and fragrances of the herb. The lifespan of the crop is about 5—6 years and usually one harvest is done in the first year and two in the following years. On average, the yield ranges from 2.5 to 3.5 tons/ha (Bernath, 1996).

The cultivation of marjoram (Origanum majorana L.) has a long historical tradition in the eastern parts of Germany. For more than 100 years marjoram has been cultivated in the area around the town of Aschersleben (Heeger, 1956). Based on this tradition, marjoram is still grown today on 550 ha in Germany. More than 95 per cent of this cultivation is practised on the small area near Aschersleben in Saxony-Anhalt. This area produces about 8 per cent of the total medicinal and aromatic cultivation in Germany. The basic cultivation requirements for growing oregano are good climatic conditions and a highly fertile soil. The fields have to be without stones. Marjoram is mainly cultivated after legumes or potatoes and it comes in the crop rotation before wheat or barley. In autumn the field has to be well ploughed and levelled, and in spring needs to be ready for sowing. Mid-April is the best time to sow marjoram. This is sown directly in the field at 0.5—1 cm depth. In August, marjoram commences flowering and reaches the right stage for harvesting (Hammer and Junghanns, 1996).

Two species of oregano, O. vulgare L. and O. syriacum L., are grown commercially in Israel for use as fresh and dried herbs. The two species have been selected from wild populations originated from Israel and Greece. The selection of high quality cultivated varieties has been the result for the availability of large genetic diversity gathered during extensive germplasm-collecting missions targeting wild Origanum populations. Because of the very small size of oregano seeds, the species perennial habit and due to the fact that the plant is harvested more than once a year, the crop is propagated by stem cuttings planted directly in the field. In Israel oregano germplasm collections are conserved both as living plants and as seed (Putievsky et al., 1996).

Scientists from Slovenia and the Federal Republic of Yugoslavia reported on experiences with oregano cultivation in different regions of former Yugoslavia (Cok and Kota, 1989; Kota and Cok, 1989; Macko and Cok, 1989). In the Istrian area, Greek oregano (O. heracleoticum L.) was introduced into cultivation in 1984, after preliminary ecological studies on species acclimation and on herb quality have been made. Cultivations have been set up on three sub-Mediterranean areas (Dvori-Isola, 260 m asl, limestone brown soils on calcareus flish, plant density 63 500 plants/ha, Smarje-Capodistria, 200 m asl, limestone brown soils on calcareus flish, plant density 57 000 plants/ha, Savudrija, sea level, terra rossa soil type, plant density 63 500 plants/ha). (Baricevic, 1996). These areas border with the Adriatic sea (45°31' lat., 300 days of growth period, average temperature in the growth period 15.2 °C, average winter temperature 5.5 °C, average rainfall in the growing period 912 mm and during winter time 139 mm, 2346 h of insulation) (Baricevic et al, 1995). In all the localities oregano plants were manually planted in May. Plants were harvested at the beginning of the flowering period and naturally dried (dry, airy and shady place) (Baricevic, 1996).

Oregano has been used in the Anatolian region of Turkey since ancient times. Records in Turkey date its use back to the seventh century BC. In this region the crop has mainly been used as a spice and as a medicine to treat various health disorders. The natural occurrence of the 23 species of oregano, reported to be indigenous to Turkey, is recorded in the following floristic regions: the Euro—Siberian, the Mediterranean (including the Aegean part), and the Irano—Turanian. The cultivation of oregano is very popular in Turkey and a marked increase in the area devoted to the cultivation of this crop has been noticed in the last few years (Kitiki, 1996). Although Turkey is one of the main oregano exporters in the world, a small amount of this crop is also being imported into the country. The largest importing country of oregano from Turkey is United States, whose import corresponds to approximately 50 per cent of the total Turkish export. With regard to the planting pattern, a distance of 45 cm between rows is found the best and also the most suitable distance for mechanisation. The best harvest time to collect the highest amount of essential oil is when 50 per cent of the plants in the field have entered flowering. In relatively small fields, harvest is usually done manually, mechanical harvesting is being recommended only for large fields. After harvesting, plants are dried in the shade. A 25 cm stack height is preferred during drying operations in order to facilitate the accumulation of essential oil content. Although drying under natural conditions is a common procedure, drying ovens operating at 30—35 °C can also been used in commercial scale production. Moisture content of 7 per cent (min) to 12 per cent (max) is required (Kitiki, 1996).

The ecogeographical characteristics of Albania, particularly its soil and climate, represent ideal conditions for the spontaneous growth of oregano in many places throughout the country, especially in Lauretum—Castanetum plant association areas. Oregano is also being cultivated in the country, but on a limited area. Three species are mentioned in the Excursionist Flora of Albania, i.e. O. vulgare L or 'red type', which is widely dispersed in the northern part of Albania, O. heracleoticum L. or 'white type', which is widely dispersed in the southern part of Albania, and O. majorana. Both types grow as perennial plants. Normally, flowering takes place in July-September for the red type and in May—July for the white type. Oregano annual production in Albania (dried leaves with 13 per cent moisture content) ranges from 550 to 600 tons, of which about 500 tons are exported (mainly to Greece, Germany and Italy). The rest of the production is used for national consumption. Harvest, processing and trading of oregano follow official standards set out by National Authorities (Xhuveli and Lipe, 1996). Two types of oregano cultivation are practised in Albania: in home gardens and in open fields. The traditional home garden cultivation is practised more in the southern part of the country. In this case, plants are grown to meet family needs only. The cultivation of oregano in open fields is not done following any particular modern agronomic criteria. As for the home gardens, seeds are taken from spontaneous populations and also being used for field cultivation. Over the last few years, the Forest and Pasture Institute of Tirana has set up a small oregano experimental field.

In Egypt, M. hortensis (O. majorana) is cultivated for its leaves and essential oil. Plants have been planted in rows (40-cm spacing between plants, 50-cm row-spacing) on newly reclaimed land (formerly belonging to the Egyptian Armed Forces) near Cairo. The soil texture was sandy with a pH of 8.3, and calcium phosphate (475 kg/ha) was added before cultivation. Plants were watered as required by a sprinkler system. Nitrogen (NH4SO4, 350 kg/ha) and potassium (K2SO4, 120 kg/ha) were applied to the soil after planting, and after each harvest. Plants were harvested 3 times during the first growing season (July 7 and October 15, 1990, and February 20, 1991), and 3 times during the second growing season (May 10, August 15 and November 15, 1991). The yield of leaf essential oil and the composition of the oil were determined after all harvests. The best yields of herb, leaves and oil were obtained from the second and third harvest of each season. The yield of vegetative tissue and the mass of leaves per plant were greater in the second year compared with the first year at all harvests, but the oil content of the leaves was lower in the second year. Total oil yields were higher in the second year (103.8 kg/ha) than in the first year (79.8 kg/ha) due to increased vegetative yields. Nine components were identified from the essential oils, and although there were qualitative and quantitative differences, the main constituent of all oils was terpinen-4-ol (26.7-41.6 per cent) (Omer et al, 1994).

Studies related to oregano cultivation

Kozlowski and Szczyglewska (1994) studied the biology of germination of O. vulgare L. seeds. Seeds of O. vulgare, obtained from the garden of the Institute of Medicinal Plants in Poznan, were stored in a non-heated room. Seeds were germinated under laboratory conditions on Petri dishes or in the Jacobsen apparatus. In the first year after harvest, germination capacity was between 60 and 75 per cent, and germination capacity was maintained for 4-5 years of storage. Germination capacity was reduced to approximately 12 per cent following storage for >5 years, seeds stored for 10 years were not viable.

The production of the culinary herbs, among them marjoram (Origanum majorana), in a system involving the use of conventional full-bed polyethylene mulch with furrow irrigation was studied by Csizinszky (1992) during different seasons: winter (December 1988-January 1989), spring (March-June 1989) and winter/spring (January-May 1990, planted after a tomato crop). Disease was not present but aphids (Aphididae), leafminers (Lyriomiza spp.), thrips (Thripidae) and whitefly (Bemisia spp.) were found in large numbers on marjoram when planted in March. In Florida, species originating from the temperate climatic zones are probably best grown during November-March, and those from the tropics during February-May or October-December.

Ecophysiological aspects of seed germination were investigated in the widely distributed Mediterranean-endemics. O. vulgare seeds had an absolute light requirement, seed germination could be promoted by green safelight or far-red light. The seeds were germinated over a relatively low temperature range, with an optimum temperature around 15—20 °C. Germination was also dependent upon the age of the seeds, old seeds germinated to a higher percentage than fresh ones. The seeds dispersed within the persistent fruiting calyces. Germination occurs within these calyces. Essential oils in the calyx strongly inhibit germination. This essential oil-induced dormancy is overcome under natural conditions by leaching of the inhibitors by rainwater. It is suggested that this dormancy operates as an adaptation strategy that prevents germination and subsequent seedling establishment during the early phase of the rainy period, which is usually interrupted by drought spells in the Mediterranean climate (Thanos et al, 1995).

An experiment was conducted to find out how humic substances affect nutrient uptake of plants. Oregano (Origanum vulgare) grown in nutrient film technique at 2 pH levels (4.5 and 6.5) in 2 substrates (peat and perlite) and at 3 levels of humic substance (0, 20 and 50 per cent v/v solutions of a peat extract). At low pH, the high concentration of humic substance resulted in a low shoot FW, perhaps caused by a toxicity of the humic substance at low pH. This was less pronounced at high pH (Kreij and Basar, 1995).

The rate and application method of bentazon(e) and terbacil for use with sweet marjoram (Origanum majorana) were evaluated in field studies at the South El-Tahrir Horticulture Research Station in Egypt during 1991-1992. Terbacil at 0.96 kg active ingredient (a.i.)/ha provided satisfactory weed control for both annual and perennial (mainly Cynodon dactylon) weeds, while bentazon was less effective. Terbacil application between the rows resulted in the highest yield of sweet marjoram. Neither the herbicides nor application methods (direct and between rows) altered essential oil yield or composition in sweet marjoram (El-Masry et al, 1995).

Trials were conducted at Monreale (400 m asl) and Villalba (650 m asl) in 1991-1993 on a local ecotype of Origanum vulgare which was planted in rows 100 cm apart at a plant spacing of 25, 50, 75 or 100 cm. Fresh herbage yields were highest at both sites in 1992. Plant density had no significant effect on yield or essential oil content. Essential oil content did not differ significantly between years (Leto et al, 1994).

In a field trial in Germany in 1995, O. vulgare was given a basal application of 40 kg N/ha and one or two top dressings of 40 kg N on 16 May or 16 June, and no supplementary irrigation or three irrigations (20 mm each) on 16 May, 16 June or 16 July. Increase in N rate decreased DM yield from 369 to 456.5 g/m2, seed yields from 16.95 to 28.81 g/m2 and ether extract from 1.92 to 2.06 ml/100 g. Irrigation increased DM yield from 371.7 to 435 g/m2 and seed yields by 12 per cent. Germination averaged 84.05 per cent and while the effects of N rate and irrigation could not be established, application of 80 kg N and 60 mm irrigation increased germination in the light to 94.66 per cent in laboratory tests. Germination capacity of seed covered with 1-10 mm depth of coarse sand or soil decreased from 62 to 8 per cent and from 84 to 15 per cent, respectively, when assessed 21 days after sowing (Kadner, 1996).

The effects of varying nutrient concentrations on essential oil yield and composition, and growth of O. majorana plants grown in a greenhouse during spring (from 13 April to 5 June 1998) and summer (from 4 June to 27 July 1998) were investigated. In spring, plants were treated with N and P, while in summer, N, P and K were supplied. In both seasons, nutrients were applied at 0, 0.3, 1.0 and 3.0 mM, but N was also applied at 10 mM. In the spring treatment, the total yield of volatile oil extracted from the leaves increased by 50 per cent as N and P levels were increased from 0 to 10 mm and 0 to 3.0 mm, respectively, and sabinene hydrate acetates and terpinene components of the oil increased with increasing N levels, but not with increasing P levels. Essential oil yield and composition were similar in all treatments during summer. Effects on growth (measured by plant weight, number of leaves and plant height) were greater in spring, where a 3-fold increase in plant fresh weight was observed when N at 10 mM was applied and a 2.5-fold increase when P at 3.0 mM was applied. In summer, increases in plant weight at 3.0 mM levels of N, P and K were 1.5-fold, under 2-fold and 2.5-fold, respectively; a slightly inhibitory effect on growth was observed at 10 mM N. Day length and temperature may have been the factors that contributed to the differences in essential oil yield and composition and plant growth in O. majorana in the different seasons (Guerrero Trivino and Johnson, 2000).

Experiments were conducted at Rio Primero, Province of Cordoba, Argentina, during 1996 and 1997, to determine efficiency of chemical control for annual weeds in oregano fields. The assays were performed on preplanted crops grown in loam sandy soil. The predominant weeds were Sisymbrium irio and Chenopodium album, less prominent were Raphanus sativus, Coronopus didymus, Polygonum aviculare, Lamium amplexi-caule, Apium leptophyllum, Stellaria media, Bowlesia incana and Carduus nutans. The following herbicides and rates were used: preplanting, trifluralin 0.96 kg i.a./ha and pendimethalin 0.99 kg/ha, postplanting, prometryn 1.5 kg/ha, linuron 1.00 kg/ha, lenacil 0.8 kg/ha and pyridate 1.125 kg/ha. The assays were done in random in blocks with four repetitions and control plots were untreated. The plots were formed by five 10-m length rows separated at 0.70 m. Recounting weed numbers and visual control percentage evaluated the control efficiency at days 21 and 49 postplanting. Recounting sprouted plants and estimating damage symptoms according to a 0—100 per cent scale evaluated the phytotoxic effect on the crop. The results indicated that at preplanting, trifluralin and pendimethalin gave a reasonable weed control, trifluralin performed better. At postplanting, prometryn was better than linuron, lenacil, and pyridate during both years in controlling weeds. None of the herbicides significantly reduced the number of plants produced at transplanting; moreover, the number of oregano plants was similar or higher than in the control. No symptoms of phytotoxicity or yield decrease were observed (Zumelzu et al., 1997).

The response of Egyptian oregano (Origanum syriacum) to N fertiliser application (0, 1, 2, 4 or 8g ((NH4)2SO4/pot) in sandy soil was studied in pot experiments in 1994—1995 and 1995—1996. Nitrogen fertiliser significantly increased plant height, fresh weight and dry weight in all cuts in both years. Plant biomass increased linearly and significantly as N application rate increased up to 4 g/pot, but increases from applying up to 8 g/pot were insignificant. Oil content increased significantly up to 2 g ((NH4)2SO4/pot), above which it tended to decrease. N application increased the essential oil content compared to the control in all cuts in both years, but 2 g ((NH4)2SO4/pot) was generally sufficient to satisfy the demands of O. syriacum. Thymol and carvacrol were the main essential oil components in all treatments, but nitrogen fertiliser application tended to increase their biosynthesis at the expense of y-terpinene and p-cymene (Omer, 1999).

Oregano and marjoram are crops for which genetic improvement is most necessary because of their high chemical and physiological heterogeneity. Crop improvement is highly recommended considering their widespread use and the great difficulties that nonuniform material may cause to the commercial sector. Taking into consideration both producers' and users' needs, efforts of any oregano breeding programme should be directed to the improvement of the following targets: yield-related parameters, e.g. growth habit, leaf/stem ratio, stress (salt, cold) tolerance, resistance to diseases and quality-related parameters, e.g. better aromatic characteristics, essential oil content and composition, antioxidant and antimicrobial properties. To achieve these goals, selection and hybridisation methods, combined with analytical controls on the variability encountered in the material, are the most appropriate tools for crop improvement. Local strains of Origanum vulgare subspecies and O. majorana (M. hortensis), as well as spontaneous hybrids (O. majoricum, O. X intercedens), are traditionally cultivated in many countries. In addition, several ornamental varieties are also present in the market. Breeding of oregano has started in relatively recent times. Breeding work has focused mainly on O. majorana, O. syri-acum, O. virens, O. vulgare subsp. hirtum and some hybrids, by using chemotaxonomy results and male sterility as tools for controlled crossings. Results so far are promising, as shown by the good results obtained in trials made with some new varieties (Franz and Novak, 1996).

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