Lettuce Production guidelines 2013 75 YEARS 1938-2013 the power of cooperation the power of cooperation the power of Enza Zaden Ronald Vriend Lettuce Breeder Index Production of young plants Young plants 4 Peat blocks 4 Production of glasshouse lettuce Planning of the crops 5 Establishing the crop 6 Planting 6 Temperature 6 Humidity 6 CO 2 6 Fertilizing 6 Irrigation 7 Leaf burn 7 Tipburn 7 Glassiness 7 Harvest 7 Production of open field lettuce Soil type 8 Establishing the crop 8 Translanting 8 Bed system 8 Planting 8 Fertilizing 9 Irrigation 9 Tipburn 9 Weed control 9 Harvest 10 Variety choice 10 Production of baby leaf lettuce Sow ing 11 Harvest 11 Packing & sales 12 Variety choice 12 Pests & Diseases Pests 13 Diseases 14 Enza Zaden | 3 Young Plants Lettuce can be direct drilled on well prepared beds but in practice nearly all crops are transplanted these days. Direct sowing is cheaper and the lettuce form a much better root system by not being limited by a soil pot or a plug cell. The disadvantages are loss of uniformity, a longer harvest period and problems with weed control. It is also possible to do two transplanted crops at the same fields. Young plants for transplanting are produced in glasshouse or tunnels in 3,5-4cm peat blocks or in similar cell pots. The pelleted seeds should be stored in sealed containers in a fridge until they are needed for direct sowing in the peat block The germination process should be carried out at 17-20°C. Temperatures above 21°C can have a negative influence at the germination process and temperatures of 28- 29°C or higher leads to seed dormancy. It is advisable to use a special germination chamber. If this is not possible, particularly in the summer months, consider to germinate the seeds in a cool place instead of a very hot glasshouse or tunnel. The germinating seeds should not be exposed to direct sunlight. After germination, the young plants are grown on at a maximum of 22-23° C, to get firm and compact plants. The cultivation time at this stage should be 50-55 days in winter and 14-20 days in the summer months. Before fully transplanting in the field, the young plants should be placed in a wind protected area outdoors for 2-3 days to allow hardening off. Most young plants for outdoor crops today come from nurseries specialized in producing and handling young plants. Mixture for peat-blocks Mixture needed for one cubic meter: 60 % Dark peat turf 40 % Dark crushed peat turf 60kg Clay granulate 2-6 mm. 2,0kg Dolomite carbonate 9,0kg Grinded limestone 1,0kg NPK 14-7-15 0,1kg Multifri (or similar Micro-element mix) containing Mg, B, Cu, Fe, Mn, Mo, Zn The peat blocks are formed with special machinery. It is important the peat mixture contains sufficient moisture in order to keep the shape of the blocks after being formed to a peat-block. Production of young-plants 4 | Enza Zaden Butterhead, Bionda, Green curled S P H 39 41 1 39 42 2 39 42 3 40 43 4 40 44 5 40 44 6 41 45 7 41 46 8 42 47 9 42 48 10 43 50 11 44 51 12 46 1 13 47 (1) 4 14 49 (2) 6 15 51 (3) 7 16 2 (4) 9 17 5 10 18 8 13 19 9 14 20 11 15 21 12 16 22 14 17 23 16 18 24 17 19 25 19 21 26 20 22 27 21 23 28 22 24 29 23 25 30 24 26 31 25 27 32 26 28 33 27 29 34 28 30 35 29 31 36 30 32 37 31 33 38 32 34 39 33 35 40 33 35 41 34 36 42 34 36 43 35 37 44 35 37 45 36 38 46 37 39 47 37 39 48 38 40 49 38 40 50 38 41 51 38 41 52 Red = artificial light Planning of the crops The cropping time of a glasshouse lettuce crop depends very much on the time of year. The main influence comes from the light intensity but also depends whether the day length is increasing or decreasing. Normally 5-6 crops can be grown per year. The tables shown on this page give the planting week (P) and the expected harvest week (H) at a given sowing week (S). Production of glasshouse lettuce Rossa S P H 39 41 1 39 42 2 39 42 3 39 43 4 39 43 5 39 44 6 39 45 7 40 46 8 41 47 9 41 48 10 42 50 11 43 51 12 45 1 13 46 4 14 48 6 15 50 7 16 2 9 17 5 10 18 8 13 19 9 14 20 11 15 21 12 16 22 14 17 23 16 18 24 17 19 25 19 21 26 20 22 27 21 23 28 22 24 29 23 25 30 24 26 31 25 27 32 26 28 33 27 29 34 28 30 35 29 31 36 30 32 37 31 33 38 32 34 39 33 35 40 34 35 41 34 36 42 35 36 43 35 37 44 35 37 45 35 38 46 35 39 47 35 39 48 35 40 49 35 40 50 35 40 51 35 41 52 Enza Zaden | 5 Production of glasshouse lettuce Establishing the crop Transplanting should take place in well worked and formed beds. Most glasshouse crops are grown in beds covered by thin white plastic with holes for the young plants at the correct plant distance. The plastic reflects light in the dark period, minimise the heat absorption of the soil in summer as well as maintain the adequate level of humidity to the soil and helps preventing soil splash to the leaves. The plastic should be changed between the crops. Planting Planting is done by hand or machine. The peat block should be planted with ¼ -½ in the soil to minimise bottom rot problems. It should not be planted higher in order to avoid drying out, which will delay the crop and reduce the uniformity. The distance varies from type to type and will normally be 18-22 per m². For Butterhead the row distance is normally 22cm with inter row distance of 22cm in summer and 25cm in winter. For Oak-leaved, Batavia and Bionda the inter row distance will be 15cm in summer and 18cm in winter. Temperature The temperature affects the growth significantly and must be correlated carefully with the light intensity. A too high temperature in the winter period results in long loose plants that will not form heads. Under low light conditions a night temperature at 4-6°C and a day at 6-10°C would be acceptable. If there are possibilities to keep a higher soil temperature, 10-15°C would be optimal. If the average temperature stays below 4°C the head forming will be delayed or even stopped. Humidity The humidity in the glasshouse will normally be between 60% till 85-90% and can be difficult to control. If the humidity gets too low the risk of tipburn increases. If the humidity gets too high, problems with fungal diseases will increase mainly Botrytis in the dark period and Bremia (mildew) in the summer. It is important to ventilate the glasshouse in time to keep humidity down when possible particularly in the dark periods. In the warm periods, depending on water quality (free of calcium and iron), sprinkling with water can help keep an acceptable humidity level at around 70%. CO 2 Lettuce responds well to CO 2 ; where possible give extra supply 1500 to 1800ppm in daylight will decrease the crop length and will increase the dry matter content. Fertilizing When the soil is prepared for transplanting, the required fertilizer should be applied and well incorporated. What is left in the ground from the previous crop, should be taken into account. The requirement per 100m² is 1,2kg N - 0,5kg P²O5 - 1,5kg K²O. If the N level becomes too high, the risk of fungal diseases and tipburn will increase. EC should be kept between 1,5 and 2,5; Ph between 6 and 7. Nitrate deficiency: Growth and formation of heads is reduced and the leaves turn yellowish in colour and thick roots are formed. Phosphorous deficiency: Reduced, rosette formed growth, dark green or reddish leaf colour. Magnesium deficiency: Leaves turn blue-green and yellowish and develop brown parts between the nerves. Boron deficiency: Rosette formed growth with dark green outer leaves, while leaves in the centre become thick often with chlorotic in nature. Foliage fertilizer: If the crop suffer from bad roots and has a lack of fertilizer uptake; foliar fertilizer like Resistart, Resistim or similar, can be used to “kick-start” the crop again. Best is, to spray in the morning, and after a few hours brush over with clean water if sunny 6 | Enza Zaden Production of glasshouse lettuce weather is expected to avoid leaf burning. Use minimum 500Liter/Ha when the solution is brought out. Resistart is an NPK solution based on Potassium phosphate consisting of 6.3% nitrogen (N), 4.2% phosphorus (P) and 6.9% potassium (K). Resistim can be used in nutrient solution or as a foliar feed, both preventive and to treat growth problems. Resistim and Resistart have a positive impact for both the plants’ root development as their ability to defend itself against diseases through an increased production of phytoalexine. This ensures a better absorption of water and nutrients and the plants gain a greater vitality and health. A preventive action can be leaf fertilizing young plants in the plant raising stage with 25g natriummolybdat (sodium molybdate) and 300g diammonium phosphate (DAP) in a 50 liter water solution for 10.000 young plants. Irrigation The need for irrigation depends on the soil type and the time of year. Strong soils that retain water well should be irrigated well before transplanting, again after transplanting and will then not need more supply until a few days before harvesting. A lighter soil, that can not keep a water buffer, will need frequent irrigation, normally given by a sprinkling system. Preferably the irrigation should be done early in the morning to let the plant dry before the coming night. Generally the crop needs 80mm under short day conditions and 100-120mm under long day conditions. Extra fertilizer can be added through the irrigation system when needed. To avoid burned leaves, it may be necessary to sprinkle with pure water afterwards. Leaf burn Internal tipburn can be a problem if the water supply is inadequate to cover the evaporation, especially in dry climates and during sunny weather. A high EC, high night temperatures and strong growth can increase the problem, which often can occur in the spring, where dark weather can change to intense sun rapidly. To prevent problems, the growth should be kept steady and not forced. There can be a need for extra irrigation during critical periods and even shading from the effect of severe sunlight. Tipburn Dry tipburn is normally seen in plants which are nearly mature for harvest. The edge at the outer leaves gets brown and dry. The first symptoms are slight curling of the leaf edge showing the under side of the leaf. This is caused by an inadequate water or nutrient supply in a strong growing crop, and occurs often in spring and autumn crops. Glassiness Glassiness can occur with high soil temperatures and a low air temperature when the roots transport more water to the plant than it can cope with causing the cells to burst. A clear night can also cause the leaf temperature to drop causing glassiness also. The cells get a “glassy” look, which can also look like tipburn and will start to rot if conditions are humid. Heating combined with good ventilation will increase the evaporation and decrease the problem. Irrigation should be reduced and given only in the morning letting the plants dry out before night time. Harvest The optimal harvest time is normally when the lettuce has formed a firm head and reached a given weight, which can vary depending on the time of year and on customer requirements. The lettuce can be cut by hand, cleaned and packed in boxes or often machine harvested and lifted together with the plastic for cleaning and packing. It is important to start cooling the lettuce immediately to improve the shelf life. Water cooling system with ice-banks gives the best result. Enza Zaden | 7 Soil type Lettuce can be grown in most soil types but the best are light sandy soils. Strong clay soil types are not suited. Good shelter from the wind is essential, especially for spring and autumn crops where temperature is important and damage to the leaf edges can be caused by too much wind. The pH of a sandy soil should be 6,0-6,3 and for a stronger soil types 6,8-7,2. Very strong clay soils should be avoided. The risk of soil borne diseases, decrease with good crop rotation. 3-4 years without crops that can host lettuce diseases between lettuce crops will reduce problems. Remember that also weeds can host lettuce diseases. Establishing the crop Before transplanting, the young plants should be hardened at a protected location for 2-3 days. In cold periods they should be covered with fleece if not placed in a tunnel. Preferably the fleece should be lifted a little over the plants. At this time it is advised to give the plants a starting fertilization: for 10.000 plants give25g natriummolybdat + 300g diammoniumphosfate in a 50 l water-solution. Afterwards the plants should be rinsed with a similar irrigation of clean water. Transplanting Transplanting is normally done with highly specialized transplanting machines. Transplanting must take place in well worked beds. After ploughing, the soil is formed into transplanting beds with a special bed-former machine. The young plants are transplanted in 3-5 rows with a row-distance at 32-40cm and a plant distance from 28-35cm depending on lettuce type and time of year. For example, mini- romaine and Little Gem types are grown at much higher densities with a density between the rows as short as 17cm. Smooth endive for processing 40x35cm up to 40X40cm while the curled TFM endive can be planted at 35x35cm. Bed system The advantage growing in a bed system is a well drained soil that will increase temperature faster in the spring and can drain more rain in wet periods throughout the season. The bed can also be covered with black plastic for transplanting in plant holes. This is quite costly, but can give a significantly earlier harvest in cold areas, will reduce soil splash to the leaves and weed problems. The plastic is placed with special machinery. Planting The peat block should be planted with ¾ in the soil to minimise bottom rot problems. It should not be planted higher to avoid drying out which will delay the crop and reduce the uniformity. With early spring planting it will be necessary to protect the crop against frost by covering with fleece or plastic. This will increase temperature and give up to 2-3 weeks earlier harvest. The cover will normally be removed by the second half of April - mid May, depending on the weather condition, cover material (fleece or plastic) and type of lettuce. It is recommended to remove the cover on a humid, overcast day without too much wind. Always watch the weather forecast before uncovering the crop as intense sun can burn especially the bigger sized crops. Keeping the cover too long on the crop will delay the heading of butterhead types for example and will encourage elongation of the leaves. Production of open field lettuce 8 | Enza Zaden Fertilizing The normal Nitrate needed for a lettuce crop is 140-165kg per Ha depending on soil type and irrigation possibility. Based on the results of the soil analysis, 30kg of Phosphor, 150-160kg Potassium, 15kg Magnesium and 15-20kg Sulphur per Ha should be given. Depending on the soil type, it is advisable to give all the fertilizer before transplanting having the effect of optimizing the size of the lettuce head. On light soil, the Nitrate fertilizer is often given 60% at transplanting and 40% 2-3 weeks later. The best is to drop the fertilizers between the rows to secure full availability for the plants, increase the utilization and avoid burning of leafs from contact with fertilizer. This is normally done together with the mechanical weed control. Where necessary (e.g. due to heavy rain), extra Nitrate may be needed and can be given via the irrigation system (10 min. time to wet the plants, then supply the fertilizer into the pipes while the irrigation is running, followed by 10 min. irrigation with pure water to wash the plants clean). Irrigation Irrigating a crop well is the key to successfully growing good lettuce! The root system of lettuce reaches 20-25cm deep at sandy soils and 25-30cm at heavier soils, which makes it necessary to irrigate several times during the growing period. Normally irrigation should be done when 30-40% of the available water in the soil is used (a deficit of 15-18mm at a medium strong sandy soil) and earlier in dry and hot periods. It is extremely important to maintain a good availability of water for the crop to avoid problems with internal and/or external tipburn. Tipburn Tipburn is a physiological disorder seen in a lettuce crop as burned leaf edges. The symptoms start as glassiness developing to necrotic spots often with a very low content of Calcium. Dry tipburn at the outer leaves in iceberg and diverse lettuce crops is not necessarily problematic. More serious is tipburn in the centre of the diverse head or internal tipburn, where the necrotic leaf edges are layered inside the head casing rot. Tipburn is often related to high summer temperatures but can also be seen under other conditions. It is important to select varieties which are strong against tipburn and to secure a good water supply and ensure a moderate nitrate supply. Treatment with calcium foliage fertilizers has little or no effect in head forming lettuce, but can have some effect in leafy types. A good root development will help prevent tipburn problems. Keep the crop a little drier two weeks after transplanting (when the plants are well settled in the soil) to force the enlargement of the root development. A strong root system will better secure the supply of water and fertilizer when needed. Young plants which are too big can increase the risk of tipburn. Weed control There are no herbicides allowed to be used to control weeds in lettuce. It is normally done by a combination of forming the planting bed at least 3 weeks prior to transplanting, combined with mechanical and often manually weed control. Forming the bed in due time before transplanting allows the weeds to germinate so they can be removed using a weeding harrow or by gas burning 1-2 times before transplanting the lettuce. Last treatment should be done direct before transplanting. Normally is used 75kg gas per Ha at speed 5km per hour. Another method is steaming the beds down to 5-7cm’s depth. This method can be very effective, but is also expensive using 3000-3500l diesel per Ha. A new technique with row steaming in 15cm rows is in development and combined with inter-row cultivation manually weed control can be avoided. Production of open field lettuce Enza Zaden | 9 Harvest Harvest is normally done by hand in one process by cutting and putting the heads in a plastic bag if the lettuce is clean and free of soil. Especially diverse types might need to be cleaned with cooled water normally done in a special line in the packing station. Icebergs are harvested and sold as whole-heads framed by a few outer leaves, often in a plastic bag. Other types of lettuce are often sold flow-packed. During harvest and transportation it is important to avoid damage by rough handling of the lettuce which may lead to decreased keep-ability and red coloration from oxidation of the white sap. Under hot and dry conditions in the summer, it is important to store the lettuce under shade in the field and to start the cooling process as soon as possible. The lettuce should be cooled down to 1-3°C and stored under at least 90% relative humidity. Vacuum cooling results in the fastest lowering of temperature which is a big advantage in the summer period, improving the keep-ability. It is important to maintain the cooling line during the transportation to the supermarkets and the end customers. Variety choice Variety choice is based on the desired product type for the sales market (size, shape and colour) the specific growing season and the soil type. The development and size might vary from light soil to a stronger soil type. Resistance is important, such as Bremia, Nasonovia and eventually root-aphids. The strength against tipburn and bolting will always be important, except for the first and last crops where speed is crucial and resistance against Lettuce Mosaic Virus can be relevant Production of open field lettuce 10 | Enza Zaden [...]... Code Races/Strains Level of resistance Lettuce mosaic LMV 1 IR Corky root Ss Downy mildew Bl 1-28 HR Nasonovia ribisnigri Lettuce leaf aphid Nr 0 HR Pemphigus bursarius Lettuce root aphid Pb Viruses Lettuce mosaic virus Bacteria Sphingomonas suberifaciens (ex Rhizomonas suberifaciens) HR Fungi Bremia lactucae Insects 16 | Enza Zaden HR www.enzazaden.com 75 YEARS 1938 -2013 Enza Zaden | P.O Box 7 1600 AA... breeding team! 12 | Enza Zaden Pest & diseases Pest Leaf Aphids Aphids are the most serious insects damaging lettuce crops There are more species of aphids causing problems of which the Lettuce Leaf Aphid (Nasonovia ribisnigri) is the most problematic since it penetrates deep into the heads of the lettuce Varieties resistant against Nasonovia offer the best protection and will normally be combined with... area with poplar wind breaks They enter the lettuce fields in June – July and work their way down to the lettuce roots Attacked crops will loose uniformity and head size as the heads tends to become loose There are some varieties with resistance and the chemical treatment against other types of aphids will also work against root aphids, and of course growing lettuce next to poplar should be avoided Good.. .Production of baby-leaf lettuce The production and selling of babyleaf is a rather new concept for leafy salads in Europe In the mid nineties the idea was introduced from the USA Very regional it was in Southern France... following the local legislations Sclerotinia 14 | Enza Zaden Pest & diseases Grey Mould (Botrytis) Grey mould is the common cause for bottom rot in lettuce It often starts where the leaves touch the soil and will spread to the entire bottom and the core of the lettuce The fungus has characteristic brownish grey spores It is important not to plant too deep, to secure the airflow to the bottom of the plant,... a soil borne fungus and can be a serious problem especially in cool and wet periods where lettuce has been grown for long periods The symptoms are yellowing next to the leaf veins followed by curling of the leaves Often the damaged parts can be cleaned off by harvesting, but as the pressure gets more severe the production must me moved to clean soil There is no chemical treatment and the crop rotation... growing days of the babyleaf crop A darker green variety will grow faster than a blond variety, and in general red varieties grow slower than a green variety in the same type Enza Zaden | 11 Production of baby-leaf lettuce The expression of red colour is brought about by a combination of light intensity, temperature alterations between day and night and the plant genetics Growing babyleaf crops in greenhouses... Wider spacing gives better aeration of the plants and a higher light penetration giving better colour on the lower parts of the plant One needs about 500 to 700 seeds per m² net, which is 0,7 to 1,0g of lettuce seed In some countries also higher densities are used, mostly when cut in a younger stage (f.i 7cm) Sowing of the naked seeds can be done with f.i a Seed-spider or a Miniair sowing machine, once... reduce the risk Botrytis An antagonist Rhizovital (Bazillus amyloliquefaciens) against Rhizoctonia has been tested with good results in the last years It has to be sprayed as early as possible on the lettuce field, best before transplanting or even better in a crop before This bacterium attacks the sclerotinias in the soil To prevent Pythium the young plants must be kept in a proper condition avoiding... Diseases The most important diseases are Bremia, Basal Rot, Botrytis and Watery Soft Rot which all can cause serious problems Downy Mildew (Bremia lactuca) Bremia is economical the most serious disease in lettuce causing the worst losses both outdoor as under glass especially in late summer and autumn where humidity and temperature gives the fungi the most optimal conditions in which to develop It can be . Lettuce Production guidelines 2013 75 YEARS 1938 -2013 the power of cooperation the power of cooperation the power of Enza Zaden Ronald Vriend Lettuce. crucial and resistance against Lettuce Mosaic Virus can be relevant Production of open field lettuce 10 | Enza Zaden The production and selling of babyleaf