Tài liệu Lettuce Production guidelines 2013 doc

Production of young plants Production of glasshouse lettuce Production of open field lettuce Production of baby leaf lettuce Pests & Diseases... Butterhead, Bionda, Green curledS P H Red

Lettuce Production guidelines

2013

75 YEARS1938-2013

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Production of young plants

Production of glasshouse lettuce

Production of open field lettuce

Production of baby leaf lettuce

Pests & Diseases

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

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

Butterhead, Bionda, Green curled

S P H

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

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%

CO2

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

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

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

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

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