Tài liệu Lettuce Production guidelines 2013 doc

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
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 for a long time ago, already known as the “Mesclun
de Provence”. Being very friendly in means of time spent for food preparing, this
product is gaining fast interest in young households, where both adults have fulltime
jobs. Also restaurants appreciate Baby Leaf as it adds to the “Fine Art of Haute

Cuisine”, by its different tastes, shapes and colours.
Sowing
The sowing is done on beds which have to be well prepared, rolled and flattened
because of the need for an equal germination and an uniform harvest. A basic
fertilizer of 60 – 70kg N, 40 – 50kg P2 O5 and 80 – 100kg K2O per hectare should
be applied before working the soil. Quantities depend also on the availability already
in the soil from previous crops. Beds need to be free from weeds, as during the
cropping period little can be done to avoid or clean from weeds.
Sowing is done on the beds in rows, with a distance of 10-12cm between and 2-3cm
within the row. 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 or twice a week depending the season. After sowing, the bed can be
covered with a thin sand layer, around ½cm to prevent the leaves getting dirty by the
splashing of water. This also reduces the weed pressure up to as much as 30%.
It is advised not to mix the seed of the varieties and types used as they might
influence each others growth and development. For instance, faster growing
varieties overshadow the slower ones; also red varieties can become less red when
not given sufficient light. Moreover, one gets an uneven product in size and less yield
than would be possible. Separate sown varieties improve quality, uniformity and
yield.
Irrigate the beds gently after sowing (small drops, not too wet, better short gifts but
more frequently).
Harvest
Depending on the period, the cropping takes in Mid-Europe the following time:
Covered crops about 8 - 10 weeks
Spring about 6 - 8 weeks
Summer about 4 - 6 weeks

Autumn about 8 - 11 weeks
As well as the variety choice, soil type and weather conditions have a big influence
on the number of 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.
Production of baby-leaf lettuce
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 in Northern Europe is not the best way to obtain the
darkest and most intense red coloured leaves.
The ready to be harvested field should be absolutely free of weeds, as they are very
difficult to be sorted out once the crop has been harvested. Fast and continuous
harvest is necessary to maintain the best quality and prevent the harvested leaves
drying out. The best period is early in the morning, eventually cooling the product
down with cold icy water and using protected transport to bring the product as
quickly as possible to the packing station. Harvesting can be carried out by cutting
machine (Ortomec, Parker, Simon or others), specially manufactured for harvest of
small leaves, like spinach, corn salad and baby leaf. Hand harvest is possible, but
the productivity is less and the harvested product often stays longer on the field and
starts to dry out too quickly.
The product is ready to harvest when 5 to 12cm long, depending on market
requirements. It should be cut at a height of about 1,5 – 2cm just above the central
growing point, to enable a re-growth for eventual second harvest as a “buffer” if for
instance cold or rainy weather delays or harms the following crops. Depending on
the leaf length, yields can reach 0,5 to 2,0 kg/m².
Packing and sales
The leaves should be washed with clean drinking water and foreign elements should
be eliminated. Afterwards the leaves must be dried by ventilation or preferably by

centrifugation. Care should be taken not to damage the leaves, as quality (oxidation)
and presentation will reduce rapidly. Keep-ability will also diminish. Then the desired
composition of type and colour is made and packed in plastic bags or flow-packed in
trays of f.i. 100, 125, 250gr. To avoid oxidation, sachets could be filled before closing
with carbon dioxide. In general well packed baby leaf can be kept in a refrigerator (8°
C) for 5 days and for approx 10 days at 1-2° C. Plan for the cooling chain to start as
soon as possible after harvesting and keep it running.
Variety choice
• The leaves should be upright growing, easy to harvest and not stick together. The
cut surface must be small and the leaves must be robust enough to be machine
handled without being too hard.
• The single leaves should be true to type, uniform in size, shape and the colour
should be shiny and well penetrated. The taste should true to type; fresh and nutty,
sweet or bitter.
• Last but not least the Bremia resistance should be as broad as possible and
eventually combined with Nasonovia resistance.
These are all priorities of the Enza Zaden breeding team!
12 | Enza Zaden
Nasonovia ribisnigri (not winged)
Nasonovia ribisnigri (winged)
Root Aphids
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 chemical protection based on the local legislations at the young plant stage and

later in the field, preferably with chemicals that do not affect predator insects too
much like Pirimicarp.
Root Aphids
Root aphids have a seasonal cycle with poplar and can be a local problem in 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 and sufficient
irrigation will also be very helpful to avoid root aphids as they dislike humid soil
conditions.
True Bugs
True bugs are often seen near wind mantles where they can cause problems in
mainly young plants. The heart can be damaged and brown necrotic spots at the
leaves can occur. Possibilities of chemical treatment depends on local legislations.
Snails and slugs
Completely clean the soil of old crops and weeds. If necessary use Nematodes,
Mesurol or Ferramol; depending on local legislations. A (very) fine smooth soil
surface helps against snails that can’t find a good shelter for their eggs.
Enza Zaden | 13
Downy Mildew
Sclerotinia
Pest & diseases
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 seen throughout the entire season. The disease gets its name from the downy
patches on the underside of the leaves and can also be seen as yellow spots on the
upper sides of the leaves.
The main precaution is the use of varieties offering as complete a resistance as
possible. The spores can be spread by wind, people and machinery. Keep a good
planting distance and use a bed system, so the leaves dry quicker (after irrigation,
dew, rain) and irrigate preferably early morning than at night time to keep the “wet
time” of the leaves as short as possible so that the spores cannot develop easily.
Rotivate the leaf debris left after harvest as soon a possibly to avoid infection of new,
younger crops.
Bremia needs 5-7hours to “geminate” at a temperature between 4-10° C. The
optimal temperature for the spores to penetrate the leaves is around 15° C. The
first symptoms can be seen at the earliest 5 days after infection. Infection can be
prevented with chemical treatment in combination with variety resistance. Local
legislation varies. Most commonly used products are Aliette, Previcur, Amistar and
Revus which all can help prevent infections but with little or no real curative effect.
The best strategy against Bremia is combined with the use of resistant varieties to
give first treatment at young plant stage at the plant-raiser, second treatment 8-10
days after transplanting and third 8-10 days after the second treatment. Important
is to use systemically fungicides with a minimum temperature of 15°C allowing the
fungicide to be adapted/transported in the plant.
Watery Soft Rot (Schlerotinia sclerotiorum)
Watery Soft Rot can be a serious problem, especially in very wet growing conditions.
The first symptoms are hanging leaves, like under dry conditions followed by a
collapse of the plant to a rotting mass finally covered by a white fungus tissue and
black scleroties.
An important way of prevention is a good crop rotation with at least three years
between lettuce crops. Other hosts for Watery Soft Rot are carrots, potatoes,
cabbage, onions, rape-seed crops and a number of weed species, so cereals will be

the best crops to use in the rotation. Chemical treatment is possible (For instance
Signum or the biological Contans) following the local legislations.
14 | Enza Zaden
Botrytis
Big Vein Virus
Bottom Rot
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, planting on plastic covered
beds will reduce the problems. In glasshouse crops it is important to pay attention
to the climate in the house. If it is too humid you need to ventilate and eventually
heat in combination. Chemical protection is possible according to local rules with for
instance Signum or Scala with best effect used preventively.
Basal rot
Next to Botrytis and Schlerotinia, various fungi or combinations of fungi can cause
bottom rot. Especially a well drained soil, wider spacing and aeration of the crop as a
good crop rotation can help prevent these diseases. It is important to avoid a too wet
soil especially in the young plant stage where the roots are less developed. There is
no chemical protection possible, but treated seed will reduce the risk.
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
that they dry out (e.g. stacked at a windy place, but also after transplanting in the
field).
Big Vein virus

The virus Big Vein is spread by 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 cycle needed is very long, more than twenty years.
Avoid other host species such as cabbage and weeds. If the crop is infected at an
early stage it can result in “dwarf growing”.
Enza Zaden | 15
Disclaimer
Code Resistances
Descriptions, recommendations and illustrations in brochures
and leaflets shall correspond as closely as possible to tests
and practical experience. This information shall be provided to
assist professional growers and users, whereby variable local
conditions must be taken into account. Under no circumstances
shall Enza Zaden accept liability based on such information
for deviating results in the cultivated product. The Purchaser
shall itself determine whether the items are suitable for the
intended cultivation and whether they can be used under local
circumstances. Current information concerning the resistances is
available on www.enzazaden.com.
The General Terms and Conditions of Enza Zaden apply to all
contracts entered into by Enza Zaden. The General Terms and
Conditions are published in this brochure and/or are further
available on our website www.enzazaden.com, are available at
the Chamber of Commerce Noordwest Holland in Alkmaar (The
Netherlands) and will be sent to you, free of charge, upon your
request.
Your attention is required for:

Resistances in varieties of our crops will be coded (see for
explanation our coding list at www.enzazaden.com), unless
indicated otherwise. In case a variety is resistant to more than
one pathogen, the individual resistance codes will be separated
by the symbol “/”.
• If in a resistance code of a certain variety reference is made to
certain strains for which the resistance is claimed this means
that no resistance is claimed to other strains of the same
pathogen.
• If in a resistance code no reference is made to strains of the
pathogen for which the resistance is claimed this means that
resistance is claimed only to certain not further specified strains
of the pathogen and herewith disclaiming any guarantee that
the variety will not be infected by the said pathogen.
Two levels of resistance are defined:
High resistance (HR) - plant varieties that highly restrict the
growth and development of the specified pest or pathogen under
normal pest or pathogen pressure when compared to susceptible
varieties. These plant varieties may, however, exhibit some
symptoms or damage under heavy pest or pathogen pressure.
Intermediate resistance (IR) - plant varieties that restrict the
growth and development of the specified pest or pathogen, but
may exhibit a greater range of symptoms or damage compared
to highly resistant plant varieties. Intermediately resistant
plant varieties will still show less severe symptoms or damage
than susceptible plant varieties when grown under similar
environmental conditions and/or pest or pathogen pressure.
16 | Enza Zaden
Scientific name pathogen ISF English name Code Races/Strains Level of resistance
Viruses

Lettuce mosaic virus Lettuce mosaic LMV 1 IR
Bacteria
Sphingomonas suberifaciens
(ex Rhizomonas suberifaciens)
Corky root Ss HR
Fungi
Bremia lactucae Downy mildew Bl 1-28 HR
Insects
Nasonovia ribisnigri Lettuce leaf aphid Nr 0 HR
Pemphigus bursarius Lettuce root aphid Pb HR
Enza Zaden | P.O. Box 7 1600 AA | Haling 1/E 1602 DB | Enkhuizen | The Netherlands |
tel +31 (0)228 35 01 00 | fax +31 (0)228 35 02 00 | | www.enzazaden.com
www.enzazaden.com
© November 2012 | Enza Zaden Beheer B.V. | Enkhuizen | The Netherlands
2012Winnaar
National Horticultural
Entrepreneur Award
Winner 2012
75
YEARS
1938-2013