Lettuce

 

Climatic Requirements Lettuce requires a relatively long cool (12 to 18 C) growing season, particularly cool nights and low rainfall at harvest time. High temperatures are undesirable. Heading is prevented and shooting to seed induced at temperatures between 21 to 26C . Lettuce is susceptible tofrost.  

 

Land Requirements Land to be used for seed production shall be free of volunteer plants. In addition, the soil ofselected fields should be well-drained, fertile and with high organic matter.  
Isolation Requirements

Lettuce is manily self-pollinated, but one to six per cent cross pollination due to insects has been reported. Seed fields must be separated from fields of other varieties, and fields of same variety not conforming to varietal purity requirements of certification, at least by 50 metres for foundation seed production and 25 metres for certified seed production.

Cultural Practices

Time of Sowing October
  


Preparation of Land Prepare the field to a fine tilth by ploughing and 3to 4 harrowings followed by leveling.


Source of Seed Obtain breeder's/foundation seeds from source approved by a seed certification agency.


Seed Rate Nursery sowing - 0.5 to 0.75 kg per hectare.


Sowing and transplanting of Seeds Seeds may be sown on raised nursery beds in rows 3 to 4 cm apart. and seedlings transplanted at a distance of 30 to 45 cm x 20 to 30 cm, when they are five to six weeks old.


Fertilisation Apply20- 25 tonnes of well-rotted farmyard manure 125 kg of Superphosphate, at the time of soil preparation and 250 as top -dressing in two doses (early spring, and in May when the stalks emerge).


Irrigation and Interculture Frequent hoeing and weeding is necessary for proper aeration of soil and to keep down the weeds. Water should be supplied to keep uniform moisture conditions in the soil. Drainage is as imporant as supplying irrigation, for excess of soil moisture may cause rotting.


Insect and Disease Control Adopt recommended IPM methods


Roguing Lettuce varieties fall in two groups namely, heading types and loose leaf types. In the first group there are: cabbage head types, having crisp leaves and head cabbage type; Butter head types, having soft smooth leaves, usually do not form the type of head typical of cabbage types; and cos types, having upright, cylindircal and rather thin heads. the second group (loose leaf tyeps) are non-heading and varieties differ in leaf shapesand sizes.
Roguing should be compelted before bolting starts in loose head varieties, or when heading is complete in heading varieties. Directo bolters, ill-formed plants, off-type plants, diseased plants affected by mosaic, yellow mosaic and wild lettuce plants should invariably be removed from time to time as required.


Harvesting and Threshing

Lettuce seeds ripen unevenly, and fully mature seed shatter readily. It is advisable to harvest when 30 to 50 per cent of the seeds in the heads show white pappus or fluff and a good number of heads after opening have turned brown or dark brown but have not shown out the pappus. the plants are cut by hand and left to dry on the ground for a few days. Later, the seeds are collected by gently shaking them.
In the case of heading varieties such as Great Lakes which donot produce flowering shoots so profusely, it may be desirable to collect the seeds periodically by shaking the tops and collecting the seeds from the burst out heads in trays.


Seed Yield The leafy types usually produce 500 to 600 kg seed per hectare. However, the variety, great lakes, produces only 100 to 125 kg seed per hectare.