EntrePinoys Atbp.

Local Name: Letsugas
Scientific Name: Lactuca sativa

Plant Description: Short, herbacios annual with succulent leaves growing from a basal rosette, often forming a head followed later by a flowering stalk.

Uses:

• Fresh, raw salad vegetable
• Beverage
• Cooked (cake, vegetable dishes)

Lettuce belongs to the Compositae (sunflower or daisy family). Lactuca sativa. It is an annual plant native to the Mediterranean area. Cultivation may have started as early as 4500 BC, perhaps initially for the edible oil extracted from its seeds. Salad lettuce was popular with the Ancient Greeks and Romans. Cultivated lettuce was probably derived from the so called wild or prickley, lettuce Lactuca sierriola. The primitive forms of lettuce were loose and leafy.

Climate

1. Optimum temperature: 15-18oC
2. High temperature induce early flowering and quality deteriorates with the accumulation of the bitter latex in the veins and leaves become tough. Temperature range 21-27ºC prevents heading and seeding.
3. Relative Humidity grows well between 65-85%
4. Cooler climates for heading types to form the compact large heads
5. Grows best at moderate rainfall under open field than under consistent heavy rain.

Head lettuce grows best at 15 to 18ºC. Germination takes place at a minimum of 5ºC, has an optimum range of 16 to 20ºC, and an optimum germination temperature of 20ºC (depending on the cultivar and type of lettuce). At soil temperatures over 27ºC germination is poor. Warm and dry conditions promote flowing and seed formation (bolting). Bolting occurs where temperatures over 20ºC are maintained day and night. Also tip burn problems are serious under this situation as is bitter flavor. Cool nights are essential for quality lettuce.

Warm sandy soils are preferred for the early harvest, loam to clay loam or peat for late production. On peat soil lettuce can be produced during hot weather. Good drainage and high organic matter content are essential. A regular supply of water is essential although high humidities and excess water close to the time of harvest can be destructive to the yield and quality of the crop. Fields low in disease must be selected. Sclerotinia drop has been the most serious production problem in the development of head lettuce as a major crop.

Nutrient Content: Useful amounts of several nutrients including Vitamins A and C; and minerals calcium and iron. The nutrient content is highest in the darker green, outer leaves. Low in calories. Each head contains 65 to 70 kilocalories.

Propagation:

1. Sexual propagation
2. Photoblastic seed - which means light is necessary for germination with 20-26oC optimum temperature for germination
3. Newly harvested seed id dormant
4. Seeds have better germination with one year of storage
5. Humid dark storage condition enhances dormancy
6. Dormancy may be broken by providing humid condition, sunlight and cool temperature (4-6oC for 3-5 days)

Types of Cultivars

1. Head lettuce - suitable for high elevation areas or cooler regions

• Crispheads or iceberg types
• Butterhead type

2. Loose leaf - more suitable for warmer regions

• Wide open & curly as Grand Rapids
• Wide open & smooth as Simpson
• Semi-open smooth as Cos or Romaine lettuce

Lettuce Crop Establishment

Seed Treatment - Lettuce germinates best at relatively cool temperatures. This crop should be pregerminated in cool rooms during the summer (seeded in modules or peat blocks) as conditions are generally too hot for good germination even if greenhouses are well ventilated.

Seeding/Planting - Begin field seeding as soon as the land can be worked. A succession of seedlings are necessary for continuous cropping in those coastal areas where lettuce can be grown throughout the summer and early fall. Coated or pelleted seed is available so precision seeders may be used. Seed sparsely to reduce thinning. Thin when two or three leaves have formed. Weed control is usually more of a problem with direct seeded fields.

Approximately 275 g of seed will provide transplants for one hectare. Direct seeding requires 1 to 2 kg per hectare unless precision seeded. Lettuce should be seeded at a depth of 0.6 cm or less.

Space rows 30 cm or more apart as determined by machinery. Plants should be spaced 25 to 36 cm apart for head lettuce, and 20 to 30 cm apart for leaf and bib lettuce. Seed sparsely to reduce thinning. Thin when 2 or 3 true leaves have formed.

For transplant production, seed is usually sown in the greenhouse in from March to July, 6 to 8 weeks before field planting. Seedlings are grown in module flats with a 4 to 5 cm spacing, in peat blocks or plant bands. Module trays may also be transplanted with lettuce seedlings. Plants should be hardened for a week to 10 days before field setting.

Thoroughly soak the soil in the flats with starter solution before transplanting. Keep as much soil as possible on the roots. When transplanting to the field, do not set the plants too deep in the soil or small pointed heads may result.

Transplanting Preparation

1. Directly sow in lokong or “speeding” trays with sterilized media ( 1 part garden soil, 1 part compost or chicken dung & 1 part sand or partially decomposed rice hulls). Soil sterilized may be done by using chemical of hot water treatment.
2. Do not provide covering after sowing to allow light penetration down to the seed.
3. Secure the sown seeds from insect by using chemical.
4. Water the seedlings early or late morning using fine sprinkler or a knapsack sprayer to maintain the ideal soil moisture. Over and late afternoon watering will encourage damping-off disease.
5. Apply starter solution one week after germination or when the seedlings show mineral deficiency. Calcium nitrate is recommended or complete fertilizer at a rate of 2.4 grams per liter of water. Application should immediately be followed with plain water to wash the solution from the leaves to prevent leaf burn.
6. Harden the seedlings one week before transplanting to acclimatize the seedlings. This is done by gradual exposure of seedlings to sunlight and reduction of water.

Land Preparation

The soil is prepared thoroughly into loose tilt by either twice to thrice plowing and harrowing. Lime may be applied after plowing to attain the recommended pH. The land may be furrowed of bedded as necessary depending on the type of lettuce, soil and climate conditions.

Transplanting

Seedlings are ready for field transplanting in 2-3 weeks from germination or when the seedlings have 4-6 leaves.

Planting Distance, System and Population Density

The distance, and system to be used would depend on the type of lettuce:

Lettuce Crop Management

Beds - Lettuce should be transplanted or seeded on raised beds if possible.

Irrigation - A steady supply of moisture is needed for good quality and yields. Irrigation must be monitored along with the weather especially when the crop is approaching maturity since excessive moisture may ruin the crop. Soil should be kept moist, just below field capacity at 75-95% moisture. (Field capacity is attained right after the excess water drains off by gravity). Water may be applied in several ways: Gravity (furrow), by sprinkler (by hand, overhead or microspray), by drip irrigation. The later type is much ideal than over head irrigation.

Plastic - Plastic mulches provide a barrier between the soil and the plant foliage. This reduces the potential for plant disease. If black plastic is used, weeds are also controlled. For those growers producing specialty lettuce for the H.R.I. trade plastic mulches should be considered or plastic tunnels may be used for early leaf and romaine lettuce production. Transplants would be set into these structures in mid April. Plans are available from your local vegetable extension specialists. Also, floating row covers are beneficial on this crop if managed for earliness and perhaps for lateness in the season.

Weed Control

• by mechanical means
• use of plastic mulch or other mulching materials
• by use of post emergence herbicides (Sethoxydim)

Lettuce Nutrition

All additions of lime and fertilizer or manures should be based on recommendations from a soil test.

Lettuce would seem to require moderate amounts of soil fertility. Some research has been done in the Atlantic area on lettuce fertility.

Manure - manures are generally not recommended due to its weed seed content and the lack of good selective herbicides registered on this crop.

Lime - should be applied to maintain a soil pH in the range 6.5 to 6.8. On peat soils the pH for optimum crop performance is 5.5 to 6.0. Under hot conditions lettuce may benefit from foliar calcium sprays to prevent tipburn.

Nitrogen - half of the nitrogen may be broadcast before planting and worked into the soil. The balance is sidedressed 3 weeks after transplanting the crop or after thinning of the seeded crop. On mineral soils up to 100 kg/ha may be required depending on manures and legume soil residue in the soil. Over application of nitrogen can result in rapid growth and tipburn.

Phosphorus - is usually broadcast before planting and worked into the soil but should be banded if possible.

Potash - should be broadcast and incorporated before planting. Lettuce is quite tolerant of salt damage so small amounts of potash may also be banded.

Sulfur - is suggested on soils low in organic matter which are being intensively cropped. Generally these are sandy soils.

Micronutrients - Boron, copper and molybdenum applications are required in organic or peat soils. Boron may be beneficial on some mineral soils. (Use .2 to .3B in the fertilizer). Minor elements are most conveniently applied in the fertilizer but may be sprayed on the soil and incorporated before planting or applied as a foliar spray(s) to the crop. Manganese deficiency may show up on high pH soils. Apply foliar sprays starting after establishment with manganese sulfate at 1 to 2 kg of manganese per hectare in 3000 L of water.

Application Method - Broadcast before planting and work in, or preferably band 5 cm below and 5 cm to one side of the seed row. Lettuce with its limited root system, is considered to be a poor feeder. Sidedress nitrogen and potash when necessary. If using transplants use a plant starter high in phosphorus.

Insect & Diseases Control (IPM with recommended pesticides)

Insect Pests

• Cutworms: Cymbush, Lannate, Permethrin, Sevin, Bait
• Thrips: Malathion, Lannate
• Leafhopper: Dimethoate, Di-syston, Lannate, Permethrin
• Aphids: Diazinon, Dimethoate, Di-syston, Lannate, Malathion, Meta-Systox, Orthene
• Leafminer: Permethrin, Trigard
• Armyworm: Cymbush, Lannate, Larvin, Permethrin

Diseases:

• Damping-off: Moisture & plant density control, Ridomil, Previcur
• Down Mildew: Ridomil, Aliete, Mabeb
• Bottom Rot: Drop: Rovral
• Yellow: Leafhopper cont rol
• Mosaic Virus: Virus free seed materials, alternate host control, insect vector control
• Tipburn: calcium nitrate
• Brown Blight: use resistant variety, crop rotation

More Pest & Diseases Control here

Harvesting and Post Harvesting Handling

This is done 5 to 7 weeks after transplanting except for heading lettuce which would be harvested after 12 weeks or more from sowing. Late harvest could increase bitterness in the leaves.

Harvest leaf lettuce as soon as the plants are large enough. Harvest head lettuce as soon as heads become firm. Harvest early in the morning, if possible, and keep cool until marketed.

Storage and Conditioning

Rapidly cooled head lettuce in good condition can be stored for 2 to 3 weeks at a temperature of 0ºC, and a relative humidity of 98% or over. Other types of lettuce have shorter storage lives. Vacuum cooling is the best treatment for quickly removing field heat to temperatures near 0ºC, and this is effective in extending the storage life of this vegetable. Wilting can be reduced by using individual polyethylene head wraps or open-topped bags in the case of leaf lettuce. Wraps should have ventilation holes to prevent the development of injurious atmospheres inside the package. Avoid storing lettuce with apples, pears, tomatoes or other products that produce ethylene. Ethylene can induce russet spotting on midribs of lettuce leaves.

Harvesting is done by cutting at the soil level using a sharp knife. It is best to harvest not too early in the morning to minimize mechanical damage. Leaves are crispy in the morning due to high water content thus, prone to mechanical injury during post harvest handling.

Cleaning by removing of the old leaves may be done in the field or in the packing house. Washing the stem end to remove soil particles is also recommended prior to packing.

Sorting, grading and packing may be done in the field or in the packing house after or during cleaning. Grades are usually based on buyer’s specification. Carton boxes are ideal packaging material especially for far distant markets.

Pre-cooling or rapid cooling (48 hours or less) to a desired transit or storage temperature soon after harvest before it is stored or moved in transit to remove field heat may help maintain the quality and prolong the shelf life of the hard head lettuce. After which they may be stored as long as 30 days at 1oC and high relative humidity.

For the leaf type or soft head lettuce, from the field, the leaf lettuce is soaked in clean chlorinated water to dehydrate. To eliminate soil particles, the lettuce is held upside down in water by the stem and gently agitated. When almost dry, each plant is packed in a perforated plastic bag or carton boxes and kept in storage for distribution.

For more information, contact:

Department of Agriculture, Regional Field Unit No. 10
Antonio Luna Street, Cagayan de Oro City
Telefax. Nos. +63(88) 856-2753 to 55; +63(8822) 728236/ 725725/ 727403/ 726475

Read Lettuce production scales up in Mt. Kitanglad

sources: www.gov.pe.ca, www.cagayandeoro.da.gov.ph, photo from worldcrops.org

This entry was posted on Monday, April 14th, 2008 at 8:30 am and is filed under Plant & Crops. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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