Hazelnut technology for warmer climates
Author:Dr. Joan TOUS MARTI
E-mail: [email protected]
Institut de Recerca i Tecnologia Agroalimentàries (IRTA)
Departament d’Arboricultura Mediterrània. Centre de Mas Bové
Apartat 415. 43280-Reus (Tarragona). Spain
Phone: +34 977-344055
Fax +34 977-344055
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Hazelnuts are cultivated in very diverse situations due to the enormous agroecological, technological and socioeconomical differences of the producing areas. Hazelnut cultivars choice and cultural practices (planting systems, pruning, sucker control, soil maintenance, fertilizing, irrigation, pest control and harvesting) and their effect on orchard management efficiency are reviewed.
The hazelnut is being cultivated in a big diversity of ecological situations, technological forms and socio-economic settings. In short, it concerns a considerable variety of “production models”, with different response capacities with respect to unfavourable market situations (table 1).
Growing conditions of hazelnuts are best in mild climates without extremes of heat and cold. Temperatures of minus 10 0C are critical, especially if accompanied by wind, which may kill both pistillate and staminade flowers. However, some winter chilling is necessary to break the dormancy period. This specie is fairly sensitive to spring frosts since the buds of cultivated cultivars open relatively early in March. Fruit set is another critical stage. At the end of May and June, maximum day temperatures should not be lower than 21 0C over a period of three days or more. If this threshold is not reached, empty nuts are formed and fall before ripening, since embryo growth has been halted at a very early stage of development.
Another constraint on this crop is the frequent occurrence of strong winds which, in winter, disrupt pollination by blowing the fine pollen out of the orchard, and, in summer, cause high evapo-transpiration, drying the leaves and halting the growth of young shoots. In this latter case, the hazelnut root system, which is not very strong, cannot entirely compensate the tree's water losses.
For these reasons it may be clear why the hazelnut is cultivated mainly in regions sheltered from very cold winter, with soft winds to improve the pollination, without spring frosts and with relatively warm weather in the early summer, regular summer rain and high humidity during the vegetative period. These conditions are most often found in zones with a maritime climate in the northern (between 400 and 45 0) and southern (310 and 41 0) hemispheres.
Although the hazelnut can be grown on very varied soils from the point of view of pH and fertility, it prefers deep, well drained fertile soils, either neutral or slightly acidic (about pH 6), and it is sensitive to root asphyxia.
Hazelnut cultivar choice and cultural practices and their effect on orchard management efficiency for the warmer climates are reviewed.
2. Hazelnut cultivars characteristics.
The hazelnut production is based entirely on cultivars selected from wild plants. Few varieties are utilised for commercial production (about 20). The characteristics of main cultivars are the following:
- 'Tombul' (Turkey): round shape fruit, ripening at medium period, high kernel percent (49.2 %), good taste and aroma and good pellicle removal. Low vigour tree with high productivity. The husk is more than twice the nut length. High-chill requirements.
- 'Tonda Gentile delle Langhe'(Italy): medium productivity, early ripening, medium nut weight, medium kernel percent (45.3 %), round shape, good pellicle removal, good taste and aroma and long storage life. High-chill requirements.
- 'Tonda Romana'(Italy): medium-high productivity, late ripening, medium nut weight, medium kernel percent (48 %), round shape, bad pellicle removal, late leafing, and good taste and aroma. Medium-chill requirements.
- 'Tonda Giffoni' (Italy): high productivity, spread out ripening, medium nut weight, medium kernel percent (48.4 %), round shape, good pellicle removal, early leafing, and good taste and aroma. Low-chill requirements.
- 'Negret' (Spain): medium tree vigour, productive, late ripening, small-medium size, medium kernel percent (48 %), long shape, good pellicle removal, and good aroma and taste. Low-medium chill requirements.
- 'Pauetet'(Spain): high vigourous tree and high yield, medium ripening, small-medium size, medium kernel percent (47 %), round-long shape, medium pellicle removal, medium leafing, and regular aroma and taste. Low-chill requirements.
- 'Barcelona' (syn. 'Castanyera' in Spain ('Fertile de Coutard' in France): it is the main cultivar in USA. High vigour and medium productivity, late ripening, high nut weight, low kernel percent (39 %), round shape, medium leafing and regular aroma and taste. Medium-high chill requirements.
The Turkish cultivar 'Tombul', the Spanish cultivar 'Negret', and the Italian cultivars 'Tonda Giffoni' and 'Tonda Gentille delle Langhe' are considered the best currently available for the industry market. For in-shell market, 'Barcelona', 'Ennis', 'San Giovanni' and 'Corabel' are prefered.
In relation to self-incompatibility of hazelnut cultivars, it is important to have pollinizers with the same anthesis time of catkins as that of female flower receptivity of main cultivars. Recommendations for frequency of pollinizers in orchards vary widely (3 to 30 %), but the best would be an average of about 10 %.
3. Cultural practices3.1. Training and tree spacing
The traditional training system in hazelnut orchards in the main production areas (Turkey, Italy and Spain) has been a multistem bush, according to its natural tendency of bushing growth. However, the training system used in the new orchards of the United States, France, Italy and Spain is in vase with only one stem. Production and agronomic aspects (suckers control, mechanized cultural and harvesting operations) have more advantages with this training system.
Tree spacing is highly variable in the different producing countries, as they depend on the fertility of the soil, rainfall, variety vigour and mechanization requirements. This last characteristic is one of the most important to be considered in new orchards and, generally, the distance between rows should not be less than 5 m. In the orchards of Oregon (USA), trained in vase, tree density normally varies from 270 to 400 trees/ha (6 x 6 m or 5 x 5 m) while in the South-West of France they oscillate between 666 (5 x 3 m) and 800 trees/ha (5 x 2.5 m). In the Italian region of Viterbo, for 'Tonda Romana' (medium vigour), row spacing of 4.5 - 5 m and 3 m between trees, with densities of 740 - 666 plants/ha. In Spain, under irrigation, tree spacing from 6 x 3 m to 7 x 4 m (550 - 350 trees/ha) is recommended, depending of the soil fertility and vigour of the cultivar.
3.2. Pruning systems
3.2.1. Training young trees
Vase is the most used training system in modern hazelnut orchards. This pruning system normally varies in the producing areas according, mainly, to the ecological conditions, vigour of the variety, quality of the plant, and the employed harvest system. In USA and France, with vigorous cultivars (‘Barcelona’ or ‘Fertile Coutard’), selected stems and orchards designed for mechanical harvesting, pruning young trees is done during the first years, leaving 3 - 4 scaffold branches and trunk height superior to 80 cm, while in Spain and Italy, where generally less vigorous varieties are used (‘Negret’, ‘Tonda gentile delle Langhe’, ‘Tonda Romana’, ‘Tonda Giffoni’, etc.), lower crown heights are used (10 - 40 cm), in order to favour crop initiation and better adaptation to adverse crop conditions. After the formation of the tree crown, the primary branches are headed and then the secondary branches, to favour the general branching of the tree and to avoid also the first fruit bearing in the shoots extremity, as in non vigorous varieties (‘Negret’) the presence of nuts in terminal shootings delays its vegetative development and causes a premature ageing of the hazelnut.
Table 1 - Summary of the most outstanding characteristics of the main hazelnut crop areas.
|1 300|| Mountain|
| Dry farming|
Neutral or acid
| Dry farming|
|1 000-1 500|
|800|| Slightly hilly|
| Dry farming / irrigation|
Bush and tree
| S. Giovanni|
|2 000-2 800|
|600-700|| Slightly hilly|
|Dry farming / irrigation Tree|| T. Romana|
|1 500-3 000|
| Dry farming|
|Camp de Tarragona|
|Irrigation Bush and tree|| Negret|
|1 500- 3 000|
| Dry farming|
|1 000|| Plane|
Neutral or acid pH
| Dry farming|
|1 700- 2 000|
| Dry farming / irrigation|
| F. Coutard|
|2 000-2 500|
3.2.2. Pruning of mature trees
Pruning of mature trees, in traditional orchards, is still a little extended practice and usually it is limited to the elimination of dry, damaged or excessively inclined branches to the ground. In this situation, we have to point out that an insufficient pruning reduces shoot vigour of the mature hazelnut trees and therefore diminishes its crop potential and increases alternate bearing, as there exists a positive correlation between crop yield and annual shoot vigour. It has been observed that branches with a yearly growth below 5 cm hardly differentiate flower buds, as shoots of at least 15 - 20 cm are needed, according to vigour and tree age, to achieve good yields. The absence of pruning causes lack of illumination, and leads to a slight and sometimes null fruiting in the low and internal part of the tree. Few pruning strategies there exist in hazelnut, standing out the proposed by European authors, who have done essays of different pruning intensities, getting more favourable crop yields with slight and yearly operations.
3.3. Sucker control
Sucker removal is a normal practice in hazelnut orchards. Traditionally it has been exercised in Turkey, Italy and Spain, by workers in winter. This system is not the most convenient, except for the first training years, as suckers after the whole vegetative period, weaken shoot growth of the tree. Now several herbicides are used, mainly Paraquat, 2,4-D amine salt, MCPA, Glyphosate + MCPA and Ammonium gluphosinate, its efficiency depends on the sucker size and number of treatments done during spring and summer. Normally, treatment is advised when suckers have herbaceous consistency (15 - 20 cm height) and repetition at least three or four times between May and August.
3.4. Orchard soil management
During the first plantation years periodicals and shallow mechanical labours have to be given (lower than 10 cm) tending to eliminate weed competition and favouring the ventilation and soil moisture. During youthful periods (until 3 - 4 years) it is dangerous to use some traditional herbicides with residual action. In substitution, others can be used like Paraquat, Oxifluorfen, Pendimentaline, etc., but avoiding to reach young trees in the treatment.
In mature orchards soil management varies according to areas, climatic conditions and harvest type. Thus in Oregon (USA) and France, the soil is normally maintained with a permanent green cover in the center of the row, with frequent flailing to avoid competition for water, and leaving the soil bare, with herbicides, in the tree row. In Spain and Italy, chemical weeding is normally practised below the tree canopies and mechanical labour between rows helping the introduction of organic material to the soil and avoiding erosion in case of torrential raining. During the last years, in Italy (Piamonte, Campania and Lazio), a natural green cover is being recommended, with two or three yearly mowing, to correct the inconveniences of soil labour in mechanical harvesting, in order to avoid the excessive dust by vacuum machines and to improve the hazelnut harvesting machines efficiency with a more compact soil between tree rows.
Nontillage below tree canopy or between rows, favours ground preparation for mechanic harvesting and reduces damage to the superficial hazelnut root system. In the majority of productive areas, except for Turkey, the use of herbicides is very generalized, in both dry and irrigated orchards. The most used herbicides in mature orchards according their application time, are: Simazine, Diuron, Napromide, Oxifluorphen, Propyzamide, Trifluraline in preemergency and Paraquat, 2,4-D, Aminotriazol, Glyphosate, Ammonium gluphosinate, Terbutilazine + Terbumeton, Fluazyfop-butyl, etc. in postemergency.
3.5. Nutrition and fertilization
Fertilization practice presents a considerable criterion diversity and application prescriptions, although there seems to exist a major coincidence when the effects of different fertilizers on the hazelnut crop are described. Nitrogen is an important nutrient for plant development and consequently for crop yield. Phosphorus acts beneficially in hazelnut during fecundation and fruiting, although response to increased doses of this element are minimum. Potassium acts as a crop quality element, as it facilitates the assimilation of nitrogen in the leaf and the increase of kernel size.
The most recommendable quantities of fertilizer given by different authors, according to the existing data, with some discrepancy, is the equilibrium 1:0.4:0.9 (N:P:K). The most appropriate fertilizer contributions, with possible variances because of environmental conditions, are 120 to 150 kg/ha of nitrogen, 60 to 70 kg/ha phosphorus and 100 kg/ha potassium, with fragmented nitrogen applications in March-April (35%), end of May (50%) and October-November (15 %) in case of shallow soils. Maybe potassium applications could be increased to assure healthier leaves in the period that follows harvesting, as it is intuited that there exists a lack of this element in the leaves at the moment that the kernel starts growing. Additional magnesium applications (mainly by foliar spray) and boron (through soil) complement the fertilizing programme.
According to the available data, it seems that standard leaf contents about 2.2 % nitrogen, 0.18 % phosphorus, 0.9 % potassium and about 0.24 % magnesium, are the most accepted values as indicators of the optimum level for sampled leaves at the end of August in Oregon and at the end of July in the Mediterranean area, which are the periods of maximum stability of mineral contents in hazelnut leaves.
The ‘Camp de Tarragona’ (Spain) hazelnut growing region, has been during many years a unique case where hazelnuts were irrigated, because in the other producing countries (Turkey, Italy, USA) the crop areas of this species were located in regions with higher rainfall and less extreme temperatures, where hazelnut presents a better adaptation to these climatic conditions. This situation has changed since hazelnuts have been introduced in new areas with less rainfall (in Italy basically), and because in other regions of France and Italy with important rainfall (700 mm per year) the necessity of irrigation has been detected in order to obtain good yields.p>
In warmer climates (Tarragona, Spain), with average rainfall about 500 mm/year, mean year supply is about 2,500 m3/ha in drip irrigation, distributed from May to September. To analyze the critic moments for irrigation in hazelnut crop training we divide its annual cycle in three characteristic stages for the producing region of ‘Camp de Tarragona’ (Spain):
a) Vegetative growing: April-May-June
b) Fruit filling (dry matter): July-August
c) Reserve accumulation: September-November
3.7. Pest management
Numerous pests and diseases can become a danger for hazelnut when their attacks exceed certain limits, most of them can be controlled by cultural or chemical means. Among pests, ‘hazel weevil’ (Cucurlio nucum L) is the worst enemy of hazelnuts in Europe and Minor Asia attacking the tender nut and producing a typical whole, destroying afterwards the kernel and causing severe damages. The bud mite, Phytoptus avellanae Nal, is present in all hazelnut producing countries. Aphids are insects in expansion in several countries (Spain, France and USA), standing out Myzocallis coryli and Corylobium avellanae. In Oregon (USA) the filbertworm (Melissopus latiferreanus) represents the main pest. Other pests are caused by Zeuzera pyrina, Eulecanium coryli, Archips rosanus and Nezara viridula.
What diseases concerns, 'anthracnose', caused by Criptosporiosis coryli, is a problem throughout Europe and Asia; the fungus attacks buds, stems and catkins of hazelnut trees, causing their desiccation. 'Eastern filbert blight', caused by the ascomycete Anisogramma anomala (Peck) E. Muller; originally observed on the American hazelnut in the eastern United States and currently it is a big problem in Oregon. 'Canker disease' caused by Cytospora corylicola Sacc., which produces the destruction of older branches, mainly in Spain and Italy. 'Sphaceloma', caused by Sphaceloma coryli can affect different parts of hazelnut, leaves, young shoots and nuts. Several other fungal diseases are known to affect hazelnuts: Botrytis cineria Pers., described in France; 'root rots' caused by Armillaria mellea (Vahl.) Pat. and Rossillinia necatrix (Hart.) Berl.; 'oidium' in the revers of the leaves caused by Phyllactinia guttata.
'Bacterial blight', caused by Xanthomonas campestris pv. Corylina is a serious disease in nurseries and young orchards in Oregon, eastern Europe, France and Italy. In layer beds bacterial blight affects stems and lateral herbaceous shoots, symptoms include necrosis and drying-out; this disease can girdle and fill young trees (up to 5 years of age).
The most significant virus affection is 'hazelnut mosaic', caused by the apple mosaic virus (ApMV). ApMV has been found in a large number of cultivars from Spain, southern Italy and Turkey. Symptoms, when present, include chlorotic ringspot, line patterns and flecking on older foliage. The virus can be readily detected in young foliage by ELISA Test.
Harvest, taking place from the end of August until half October, constitutes one of the most important crop costs. Hazelnuts are harvested on the ground, picking them up in one or two operations. At present, harvest is quite mechanized, except for Turkey where the fruit is collected by hand from the tree. In the remaining producing countries, there are three generalised harvest systems: harvesting by metallic broomer or blower followed by mechanical cleaning, used in mountain areas of Tarragona and Italy; harvesting by vacuum machine, is the mechanical system in plane areas of Spain and Italy, and harvesting by sweepers and pickup machines is the system diffused in big orchards of Oregon (USA) and France.
Generally, this last harvest system consists of two machines: a sweeper-windrower, self-propelled or coupled to a farm tractor, and a hazelnut pickup machine of high yield. The optimum yearly labour surface for this machine is about 40 ha. These pickup machines are quite big, they require flat soils and wide tree spacing, and just one operator is needed. They have a good harvest yield, of about 800-900 kg/hour, that represents about 2-3,5 hours/ha; in French orchards they allow to harvest about 4 ha per day.
This harvest system is very fast and reduces very much the costs of this operation. The present tendency of new orchards in the Mediterranean and other countries (Australia) has to be oriented to the introduction of these mechanical pickup systems.
4. Conclusions4.1. Cultivars choice
The Spanish cultivar ‘Negret’, and the Italian cultivars ‘Tonda Giffoni’ and ‘Tonda Romana’ are considered the best currently available for the industry market in the warmer climates. For in-shell market, ‘Barcelona’ and ‘San Giovanni’ are prefered in these areas.
4.2. Agronomic aspects
As follows some conclusions are described about the studied cultural techniques, and several trends are suggested to improve the orchard productivity.
* Training systems and tree spacing:
Tree training in vase with only one stem seems to be the most useful. What tree spacing, concerns, distances between 6 x 3 and 6 x 4 m are recommended. In some, a setting of 5 x 3 m can be chosen (little vigorous varieties and poor soils) or 7 x 4 m, in case of vigorous varieties, fertile soils and in irrigation.
* Pruning systems:
Training young trees: use quality stems and, according to the cultivar vigour, cut the trunk not too high (50 - 80 cm) to form the vase of the tree. Then, the primary and secondary branches are headed for canopy branching. With respect to pruning of mature trees: light pruning of the canopy can be recommended, each two or three years. It could be interesting to make a profound study of mechanical pruning.
* Sucker control:
Chemical control of hazelnut suckers is recommended. The most convenient herbicides are several, pointing out 2,4-D amine salt, Paraquat, Glyphosate + MCPA and Ammonium gluphosinate. Varietal behaviour studies about hybrid rootstocks without sucker emission of C. colurna x C. avellana are done.
* Soil management :
In warmer climates, nontillage or a temporary green cover could be implanted between rows to facilitate the integral mechanization of harvesting in modern orchards. In spring, and later on, it should be eliminated it with herbicides or flail movers in order to get a more compact soil during the passage of the harvest machines.
The most appropriate fertilizing contributions per ha, with possible differences because of environmental conditions, range from 120 to 150 UF nitrogen, 60 to 70 UF phosphorus and 100 to 120 UF potassium, with fractional applications of nitrogen. Additional contributions of magnesium and boron complement the fertilizing scheme.
It seems very important to supply enough water to hazelnuts during their vegetative cycle. It is interesting to point out the effect of water stress during the kernel filling. For the region of Tarragona (warmer climate), yearly contributions of 2.500 m3/ha or more are recommended. Adapt them to punctual necessities is very important, specially in orchards with shallow soils. It is advisable to follow the indications of the climatic stations network, where available. A good irrigation installation and a convenient management are basic aspects for a better water irrigation utility.
Harvesting constitutes one of the most important production costs and its value depends of its mechanization degree. The machine types used in the orchards in USA and France are the most convenient, because of their speed in picking up the fruit from the ground and because of their low labour costs.
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