Lettuce Farming

Introduction

Lettuce, scientifically known as Lactuca sativa, belongs to the Asteraceae family. It is an annual plant that is commonly cultivated as a leafy vegetable, although its stem and seeds are also occasionally used. Lettuce finds its primary use in salads, but it can be incorporated into various dishes like soups, sandwiches, and wraps. Additionally, it can even be grilled.

While lettuce is not widely recognized or consumed in many Kenyan households, its popularity and acceptance are gradually increasing.

Nutritional & Health Benefits of Lettuce

Lettuce offers several benefits, including:

  • Controlling inflammation: Lettuce contains proteins like lipoxygenase and carrageenan, which assist in managing inflammation.
  • Preventing cholesterol oxidation: The combination of vitamin C and beta-carotene found in lettuce helps prevent the oxidation of cholesterol.
  • Promoting sleep: Lettuce contains Lactucarium, which possesses relaxing and sleep-inducing properties, making it helpful for insomnia.
  • Supporting bone health: Lettuce is a rich source of vitamin K, which plays a potential role in bone metabolism.
  • Providing essential nutrients: Fresh lettuce leaves contain significant amounts of folates and vitamin C, contributing to a nutritious diet.
  • Supplying important carotenoids: Lettuce contains zeaxanthin, an essential dietary carotenoid.
  • Offering vital minerals: Lettuce is abundant in minerals such as iron, zinc, calcium, potassium, and magnesium, which are crucial for body metabolism.
  • Providing B-complex vitamins: Lettuce is a rich source of B-complex vitamins like thiamin, vitamin B-6, and riboflavins.
  • Rich in fiber: Lettuce is high in fiber and cellulose, promoting healthy digestion.
  • Possessing antimicrobial properties: The latex of lettuce contains terpenes, cardenolides, and enzymes like glucanases, which exhibit antimicrobial properties against yeasts.
  • Anti-cancer properties: Lettuce has been found to possess properties that may help in preventing certain types of cancer.

Seed selection

There are two main types of lettuce: heading and non-heading varieties. The heading variety forms a tightly compacted head similar to a cabbage, while the non-heading variety has loose leaves.

Here are some commonly grown varieties of lettuce:

  • Butterhead: This variety has loose leaves and a buttery texture. It is typically ready for the first harvest around 45-55 days after sowing.
  • Crisp-head: Crisp-head lettuce forms tight and dense heads resembling cabbage. It is known for its mild flavor and crunchy texture. The first harvest is usually ready in 70-100 days after sowing.
  • Loose-leaf: Loose-leaf lettuce has tender, delicate, and flavorful leaves that form a loose bunch. It is primarily used for salads and can be harvested around 45-55 days after sowing.
  • Romaine lettuce: Romaine lettuce grows into a long head with sturdy leaves and a prominent rib that extends almost to the tip of the leaf blade. It is commonly used in salads and sandwiches and can be harvested approximately 75-85 days after sowing.
  • Chinese lettuce/Celtuce: This variety forms long, tapering leaves that do not develop a tight head. It is characterized by a strong-flavored cluster of terminal leaves.
  • Summer crisp: Summer crisp lettuce forms moderately dense heads with a crunchy texture. This variety falls between crisp-head and loose-leaf varieties in terms of characteristics.

These different lettuce varieties offer a range of textures and flavors, allowing for various culinary uses and preferences.

Ecological requirements

Lettuce is a crop that thrives in cooler seasons, with optimal growth occurring within temperature ranges of 12-20°C. High temperatures exceeding 27°C can negatively impact head development, the quality of the edible plant parts, and can even trigger premature seed stalk formation. While lettuce can tolerate various soil types, the best production outcomes are achieved in well-drained, fertile loam soils. These soils should have a rich organic matter content, good water-holding capacity, and a pH level ranging between 5.5 and 7.0.

Propagation & Planting

Lettuce is reproduced through the use of seeds, which can be either directly sown into the main field or first grown in a nursery bed and then transplanted into the desired location.

Raising seedlings

  • Begin by preparing a nursery bed that is approximately 1 meter wide and matches the desired length.
  • Apply a solution of Pyramid® 700WP (100g), Loyalty® 700WDG (10g), and Optimizer® (20ml) mixed with 20 liters of water to saturate the soil. This mixture serves multiple purposes, such as controlling soil pests and diseases, providing nutrients, breaking seed dormancy, and promoting uniform germination.
  • Plant the seeds at a depth of approximately 2cm and lightly cover them with soil.
  • Place a thin layer of mulch over the nursery bed to cover it.
  • Ensure the nursery bed is regularly watered.

The seeds will typically take around 3-4 days to germinate.

Transplanting

The lettuce seedlings reach transplant-ready stage after 4-5 weeks, characterized by having 4 to 6 leaves and a well-developed root system. To prepare the young plants for transplantation, it is recommended to gradually reduce the rate of irrigation and remove shading starting one week before transplanting. Prior to lifting the seedlings, it is important to irrigate the nursery bed.

Procedure:

  1. Create raised or sunken beds on the prepared land.
  2. Combine the soil with manure and DAP. To enhance nutrient uptake, stimulate root development, and achieve other benefits, mix 1kg of Humipower® with 50kg of DAP and/or 1 ton of manure.
  3. Irrigate the beds to ensure suitable conditions for planting.
  4. Plant the seedlings in the beds, maintaining a spacing of 45*30cm.

Tips:

  1. To mitigate transplant shock, apply a spray of Optimizer® at a rate of 10ml per 20L of water to the seedlings.
  2. Optimal timing for transplanting is either early in the morning or in the evenings.
  3. Select only healthy and robust seedlings for transplantation.

Cultural practices

Thinning: When seedlings reach a height of approximately 2-3 inches, it is advisable to thin them out, leaving a spacing of 3-4 inches between each plant. This practice reduces competition among the seedlings and promotes proper air circulation within the crop.

Weeding: Regular weeding is essential for lettuce, as it does not compete well with weeds. Weeds should be removed consistently until the foliage of the lettuce plants covers the ground. Afterward, it is sufficient to pull out individual weeds as they appear.

Mulching: Mulching the crop is recommended to retain soil moisture and keep the produce clean. As the mulch decomposes, it releases nutrients into the soil, which are then absorbed by the crop.

Watering/Irrigation: To ensure uniform and vigorous growth, it is important to maintain moderate soil moisture levels throughout the season. Insufficient watering may cause lettuce to become bitter and flower prematurely.

Crop rotation: Strict adherence to crop rotation is crucial, utilizing non-related crops such as cereals, legumes, brassicas, and others. This practice helps prevent the accumulation of pests and diseases, among other benefits.

Fertilizer application: Applying both basal and foliar fertilizers in a timely manner is highly recommended to achieve optimal yields. Incorporating well-decomposed farmyard manure is especially beneficial for soils with low organic matter, as it enhances productivity without harming soil structure or polluting the environment. Additionally, it provides residual effects in the soil that benefit subsequent crops in the following seasons.

For example:

During the transplanting process, it is recommended to apply 50kg of DAP or TSP per acre. These fertilizers are rich in phosphorous, which is crucial during the early developmental stages of the crop. After two weeks, it is advisable to spray the young plants with either Lavender Super Starter® (20ml/20L) or Goldchance Super Start® (50g/20L). This application promotes rapid root development, ensures balanced crop growth, and enhances the crop’s resistance to infections and weather-related stress.

Two weeks after transplanting, perform a top dressing using 50kg of CAN or NPK per acre. Additionally, after four weeks, apply the same rate of 50kg per acre. Subsequently, spray the crop with either Goldchance Super Growth® (50g/20L) or Lavender Super Growth & Vegetative® (20ml/20L). This foliar application promotes faster vegetative growth, increases the crop’s resistance to infections and weather stress, and ensures balanced crop growth.

Other foliar fertilizers that can be utilized include Optimizer® (10ml/20L), Goldchance Multisuper K® (50g/20L), Zinc Gold® (10ml/20L), and Biodistinction Xtra®.

Maturity, Harvesting & Post-Harvest Handling

The time required for lettuce to go from planting to harvesting ranges from 45 to 130 days, depending on the variety and ecological conditions. Furthermore, the stage at which lettuce is harvested depends on the lettuce variety and the intended purpose. For example, lettuce varieties that bolt and produce flowers tend to become bitter and unsuitable for sale. Therefore, lettuce plants grown for consumption are typically not allowed to reach full maturity.

Heading types of lettuce are harvested when the heads are fully grown and firm, while loose leaf varieties are picked when the leaves have reached the desired size. Harvesting involves cutting off the plant just above the soil surface to retain most of the outer leaves around the head. It is advisable to harvest lettuce early in the morning as it wilts quickly. Harvesting lettuce during cooler weather generally results in sweeter-tasting and crisper leaves.

If lettuce is left in the ground for too long, it starts to produce a seed stalk, a process known as bolting, and the leaves become bitter.

After harvesting lettuce, it is important to sort and grade the leaves or heads before packing them in crates or cartons. Lettuce can also be stored for up to three weeks at a temperature of 4°C with 95% relative humidity.

Major Pests & Diseases

Insect pests

Aphids: Aphids are the most significant pests that can cause physical damage and act as carriers of lettuce mosaic virus. High populations of aphids can lead to stunted growth in young plants, and their presence can contaminate lettuce heads. They secrete honeydew, which promotes the growth of sooty mold, affecting the appearance of the produce.

Recommended sprays for aphid control:

  • Kingcode Elite® 50EC: 10ml/20L
  • Lexus® 247SC: 8ml/20L
  • Pentagon® 50EC: 10ml/20L
  • Loyalty® 700WDG: 5g/20L
  • Emerald® 200SL: 10ml/20L

To remove sooty mold, spray with:

  • Jambo Clean®: 100ml/20L

Cutworms: Cutworms are primarily problematic during the seedling stage and are usually found 2-5cm below the soil surface. They are active at night and cut stems either just above or below the soil surface.

Recommended soil drenches for cutworm control:

  • Profile® 440EC: 60ml/20L
  • Pentagon® 50EC: 20ml/20L

Diamond Back Moth (DBM): DBM larvae are green caterpillars that feed on leaf tissue, excluding the veins. Infestations can cause significant losses if not controlled.

Recommended sprays for DBM control:

  • Escort® 19EC: 10ml/20L
  • Baciguard® 16WDG: 15g/20L
  • Lexus® 247SC: 8ml/20L

American bollworm: The larvae of the American bollworm penetrate the lower part of the leaves and tunnel their way into the lettuce heads.

Recommended sprays for American bollworm control:

  • Kingcode Elite® 50EC: 10ml/20L
  • Pentagon® 50EC: 10ml/20L
  • Baciguard® 16WDG: 15g/20L

Diseases

Damping off: Damping off is a soil-borne disease that primarily affects seeds and seedlings. Infected seeds fail to germinate, while seedlings rot and eventually die. The roots of infected seedlings display a white cottony growth.

Recommended treatment for damping off:

  • Drench the planting holes/soil with Pyramid® 700WP: 100g/20L
  • Spray the plants with Absolute® 375SC: 10ml/20L

Downey mildew: Downey mildew is characterized by light green to yellow areas on the upper surface of leaves. As the disease progresses, infected tissues turn brown, and a white downy mold forms on the lower leaf surface.

Recommended treatment for downey mildew:

  • Spray Gearlock Turbo® 250WP: 25g/20L
  • or Fortress Gold® 720WP: 40g/20L
  • or Tower® 720WP: 50g/20L
  • or Katerina® 720SC: 40ml/20L

Leaf spot: Infected plants exhibit small, yellowish spots on the outer leaves. These spots enlarge and become large, irregular, and brown, with a pale creamy brown center and numerous black dots.

Recommended treatment for leaf spot:

  • Spray Chariot® 500SC: 20ml/20L
  • or Ransom® 600WP: 15g/20L
  • or Domain® 250EC: 10ml/20L
  • or Absolute® 375SC: 10ml/20L

Powdery mildew: Powdery mildew is a common disease that negatively affects crop quality. Symptoms include patches or spots of white to grayish, powdery growth. Small, spherical structures may appear and change color from white to yellow-brown and finally black.

Recommended treatment for powdery mildew:

  • Spray Ransom® 600WP: 15g/20L
  • or Chariot® 500SC: 20ml/20L
  • or Domain® 250EC: 10ml/20L
  • or Absolute® 375SC: 10ml/20L

Sclerotinia rot: Infected plants initially wilt on hot days, and a severe wet rot is observed near the stem and roots. A white, cottony mold develops on the rotten tissue, accompanied by hard, irregular, black sclerotia. The outer leaves wither and drop, followed by inner leaf rot if the base is affected.

Recommended treatment for Sclerotinia rot:

  • Drench the soil with Gearlock Turbo® 250WP: 50g/20L
  • or Pyramid® 700WP: 100g/20L

Bacterial rot: Symptoms of bacterial rot include water-soaked leaf spots that later turn brown, resulting in soft rot and death of affected tissue. The disease is more prevalent in hot and humid weather conditions and can worsen after harvesting, during transit, and in the market.

Recommended treatment for bacterial rot:

  • Spray Green Cop® 500WP: 50g/20L, a copper-based product that suppresses the activity of the pathogen.

Lettuce Mosaic: Lettuce Mosaic is a viral disease that causes vein clearing, mottling, curling of leaves, and increased marginal frilliness in early infections. Infected mature plants are stunted, yellow, and unsuitable for harvest. The disease is transmitted by the green peach aphid.

Recommended treatment for Lettuce Mosaic:

  • Control aphid vectors using:
    • Kingcode Elite® 50EC: 10ml/20L
    • or Lexus® 247SC: 8ml/20L
    • or Pentagon® 50EC: 10ml/20L
    • or Loyalty® 700WDG: 5g/20L
    • or Emerald® 200SL: 10ml/20L

Remarks

  • When using foliar sprays, it is advised to mix the chemical with Integra® at a rate of 3ml per 20L. Integra® acts as a sticker, spreader, and penetrant, enhancing the effectiveness of the product.
  • Optimizer® is an organic bio-stimulant that plays a vital role in plant growth and stress management. It can be applied at any stage of crop growth and development.
  • It is important to adhere to the post-harvest interval (PHI) and re-entry interval (REI) specified for the chemicals used.
  • To enhance efficacy, mix all basal fertilizers with Humipower® at a rate of 1kg of Humipower® per 50kg of fertilizer.
  • After harvest, it is recommended to store lettuce under shade to prevent wilting.
  • Conducting soil analysis is advisable to determine the fertility level of the soil.
  • The market demand for lettuce is relatively high, with potential opportunities in institutions such as hospitals, supermarkets, open-air markets, and others.

 

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