Causes and countermeasures of bolting of lettuce

Lettuce (scientific name: Lactuca sativa L.var. AngustanaIrish.) also known as lettuce, a variety of lettuce in the Compositae family that forms fleshy tender stems and is herbaceous in 2012. Alias stem lettuce, lettuce bamboo shoots, green shoots, lettuce. Delivery period: from January to April. It is native to Central or North China. The aboveground stem is edible, the stem skin is white-green, the stem is crisp and tender, the young stem is emerald green, and turns white-green after maturity. Mainly edible fleshy tender stems, which can be eaten raw, salad, fried, dried or pickled, and tender leaves can also be eaten. Stems and leaves contain lettuce and lettuce (C11H14O4 or C22H36O7). It tastes bitter and has analgesic effect. Lettuce has strong adaptability and can be cultivated in spring and autumn or overwintering, mainly in spring and harvested in summer.

Morphological characteristics of lettuce

The stem looks like a circle, like bamboo shoots. Straight roots, most of the lateral roots after transplantation, shallow and dense, mainly distributed in the 20-30cm soil layer. The stem is shortened. Leaves alternate, lanceolate or oval, etc., light green, green, dark green or purplish red in color, leaves spreading or wrinkled, entire or notched. The shortened stem gradually elongated and thickened with the plant growth. after the stem tip differentiated into flower buds, the stem grew thicker while the flower stem elongated, forming a rod-shaped fleshy tender stem. The flesh is light green, emerald green or yellowish green. Panicle with yellowish flowers, each inflorescence with about 20 flowers, self-pollination and sometimes cross-pollination. Achenes, black-brown or silver-white, with crown hairs.

Causes and countermeasures of bolting of lettuce

Lettuce has been cultivated throughout the year for four seasons in many places. However, in the cultivation, the plants are often prone to the early bolting phenomenon of few decimals of leaves, sparse stem details, long and high tender stems as sticks, which affect the yield and reduce the quality. After summarizing the production experience in recent years, the reasons for the high bolting of the tender stem of lettuce and its effective countermeasures are mainly in the following 10 aspects.

1) improper selection of varieties. There are many varieties of lettuce, and their adaptability and sensitivity to light and temperature are different. often, early-maturing varieties have stronger tolerance to low temperature and weaker tolerance to high temperature than middle and late varieties, and are more sensitive to high temperature and long sunshine.

Countermeasures: therefore, suitable varieties should be selected according to the cultivation season. For example, because the lettuce harvested in spring and autumn grows under the conditions of high temperature and long sunshine, the middle and late maturing varieties with high temperature tolerance and slow response to long sunshine should be selected, and the early maturing varieties are easy to bolting. The early-maturing varieties planted in early spring have the advantages of early listing, high yield and good benefit. If they are planted late, they are easy to bolting due to the increase of temperature and sunshine in the later growth stage, and the yield is low and the benefit is poor.

2) unsuitable sowing date. In the cultivation of spring lettuce, if the seedling is sown too early in autumn, the growth period before winter is long, the seedling is too large, and the flower bud differentiates early, it is easy to suffer frost injury and bolting early in the following year; if the sowing is too late and the growth period before winter is short, the seedling is small, the nutrient accumulation is less, overwintering is also vulnerable to freezing injury, and the next year is listed late. If the summer lettuce sows too late or the autumn lettuce sows too early, the temperature and sunshine in the seedling period are high, and the seedlings are easy to grow.

Countermeasures: therefore, attention should be paid to the appropriate sowing time for lettuce cultivation. Generally, spring lettuce is sowed in the open field in early October, protected land is carried out around late January of the following year, summer lettuce is sowed in early April, autumn lettuce is sown in early August, winter lettuce is suitable for sowing in late August.

3) poor management at seedling stage. Excessive sowing rate, dense seedling emergence, untimely seedling squeezing, partial application of nitrogen fertilizer in seedling bed, excessive watering, overshading and untimely removal of mulch during seedling cultivation can lead to excessive seedling growth. Therefore, the purpose of seedling management should be to control overgrowth and cultivate dwarf and strong seedlings.

Countermeasures: the bottom fertilizer of seedling bed is mainly organic fertilizer, which can be mixed with appropriate amount of compound fertilizer; appropriate amount of sparse sowing, and time seedlings, controlled watering, it is appropriate to make the bed soil dry and wet, shading seedlings should gradually cover the mulch late after the whole seedling and no longer shade after 3 leaves; summer and autumn lettuce seedlings can be sprayed with 500 mg / kg solution of 500 mg / kg at seedling stage, which can effectively prevent overgrowth.

4) planting is not in time. If the seedlings are not planted in time, the seedlings often grow too fast, and the Hypocotyl elongates in a state of overgrowth, so it is difficult to obtain fat tender stems after planting.

Countermeasures: generally, the suitable age seedlings with 5 or 6 leaves should be planted in time, the seedling age of autumn sowing and spring harvest is about 40 days (days), the seedling age of spring sowing and summer harvest or summer harvest is about 25 days (days), and the seedling age of autumn sowing and winter harvest is 30 days (days).

5) cultivation is too dense. The planting density was too high, and the rosette leaves were ridged before they were formed, resulting in plant crowding and lack of light.

Countermeasures: under normal circumstances, spring harvest lettuce can be appropriately close planted for early benefits, with 8000 plants per mu; summer harvest lettuce should be sparsely planted because of high temperature and long-day light, and it is better to plant 5000 plants per mu; autumn harvest lettuce has a suitable temperature in the later stage. 7000 plants can be planted per mu, with good marketability and high yield.

6) less ploughing and loosening soil. After planting, fertilization, watering and rainfall are easy to cause soil hardening, high humidity and poor ventilation. If the soil is not ploughed in time, it will affect the growth of the plant root system and the absorption of water and fertilizer, so that the leaves can not get enough water and fertilizer, and the plants with weak stems and weak stems are easy to appear.

Countermeasures: therefore, after planting slow seedlings, we should plough in time, hoe deeply and thoroughly, so as to facilitate squatting seedlings, promote root development, and increase the number of rosette leaves and the growth of tender stems.

7) the amount of water is not suitable. After lettuce planting, if too much watering or Rain Water is excluded in time under the condition of insufficient fertility, the soil moisture is too high, and the tender stem is easy to grow and "waterlogged", while under the condition of soil drought and high temperature, the tender stem grows weakly and is easy to "dry run".

Countermeasures: therefore, the cultivation of lettuce should be watered properly to prevent both "waterlogging" and "drought". Before rosette leaf formation and plant ridge sealing, watering should be properly controlled so that the border surface should be dry and wet; after ridge sealing, the water supply should be increased to keep the border surface moist to ensure the rapid growth and expansion of tender stems.

8) insufficient fertility or partial application of nitrogen fertilizer. Insufficient base fertilizer or untimely topdressing, low soil fertility, inhibition of plant vegetative growth, will accelerate reproductive growth, but also prone to immature bolting. The partial application of nitrogen fertilizer can easily cause the plant leaves to grow excessively and accumulate less nutrients, and often the young stems will rise and grow before the young stems are developed.

Countermeasures: therefore, base fertilizer should be fully applied, 4000 kg of rotten manure and 25 kg of compound fertilizer can be applied per mu, so as to combine organic fertilizer with compound fertilizer. In addition, slow seedling fertilizer, plant fertilizer and shoot fertilizer should be applied in time, and ammonium sulfate or urea should be applied 15 kg per mu or 1000 kg of dilute dung water each time.

9) the climatic conditions are not suitable. When lettuce is cultivated late or planted in summer and autumn, under the condition of high temperature and long sunshine, the leaf differentiation is often less, the flower bud differentiation is early, the flower organ develops rapidly, and the management is a little careless, which is easy to cause overgrown bolting and affect the quality and yield.

Countermeasures: in addition to strengthening the management of water and fertilizer, regular spraying of dwarf is an effective measure to control bolting of lettuce cultivated in high temperature season. Spraying Daizhuangsu can delay bolting of lettuce, promote leaf growth, increase plant nutrient area and thicken tender stem. Spraying usually begins at the rosette stage, once every 7-10 days, for a total of 2-3 times, with a concentration of 350 mg / kg.

10) the harvest is not timely. The suitable time for harvesting lettuce is the "flat mouth" of heart leaves and outer leaves. Especially the late spring bamboo shoots, summer bamboo shoots and autumn bamboo shoots growing in the high temperature season often form flower buds before harvest. If they are not harvested in time, the tender stems will quickly jump high and bolting.

Countermeasures: if the harvest and supply is delayed, pinching and removing buds can effectively control the high bolting of tender stems, that is, to remove the top growing point or buds of lettuce in a sunny day in the "flat mouth" period. The unroofed plant can inhibit the top growth, increase the return of nutrients from the stem, prevent the hollow stem of the tender stem, promote the hypertrophy of the bamboo shoot, harvest 5 / 7 days later and increase the yield by 10% / 20%.