Problems and Countermeasures in Winter Forcing Cultivation of Witloof Chicory

Witloof chicory, also known as Belgian endive, chicory witloof and French bitter chicory, is a biennial or perennial herbaceous plant of the Asteraceae family, grown for the chicons produced by forcing the fleshy roots after harvest. The chicons of witloof chicory are cream-colored, slightly bitter with a sweet note, extremely crisp and tender, and can be eaten raw or made into a delicious, appetizing salad. In particular, the chicons contain bitter compounds not found in ordinary vegetables, such as aesculin, lactucin, lactucopicrin and intybin, which have liver-protecting and bile-promoting health benefits, making it a aristocratic vegetable,, and highly favored by people. Because witloof chicory chicons require a second round of cultivation to form the product, and the forcing technique is relatively difficult, problems such as rotting of the fleshy roots, rotting of the chicons, loose chicons, undersized chicons and greening can easily occur in production, greatly affecting the yield and quality of the product, preventing the production potential from being fully realized and resulting in low economic returns. After years of production practice, the author has put forward targeted countermeasures to solve these problems, and the results have been very obvious.

1 Problems and causes

1.1 Rotting of fleshy roots. The fleshy roots are harvested too late, or after harvest the storage temperature is below 0°C, causing freezing damage to the fleshy roots; or during cultivation, the petioles left at the top of the root are too long and the soil moisture is too high, both of which can cause rotting of the fleshy roots.

1.2 Rotting of chicons. The main cause is wounds at the root crown during cultivation and relatively high air humidity, which favors the spread of pathogens.

1.3 Loose chicons. During forcing cultivation, when the temperature exceeds 21°C, the chicons grow too fast, the heads are loose, and premature bolting is likely to form, causing the chicons to open up. At the same time, the chicons taste bitter and are not crisp; quality declines.

1.4 Undersized chicons. During forcing cultivation, if the temperature of the 10-15cm soil layer remains below 6°C for a long time, or the soil layer is too dry, the air humidity is too low, or the fleshy roots are small, the chicons will be undersized and the yield relatively low.

1.5 No main chicon. If the petioles at the top of the root are cut too short during processing, damaging the growing point, then no main chicon will grow during forcing cultivation, and only side chicons will be produced.

1.6 Greening of chicons. If the forcing site is not strictly shaded, or if it is frequently uncovered to let in light during cultivation, the chicons will turn green in the light, the heads will open up, and quality will deteriorate.

2 Measures to take

2.1 Guard against freezing damage. Before hard frost and soil freezing, when the local minimum temperature drops to ~2°C, dig out the fleshy roots in time, remove the root tips and lateral roots, keep the upper 20cm of the fleshy roots, and stack them in place with the leaves and roots together, leaves facing outward and roots facing inward, forming small conical piles about 1m in diameter to prevent the fleshy roots from freezing and losing water. Air-dry for 2-3 days to promote wound healing, then sort the fleshy roots according to standard and store them at 0-2°C, waiting for forcing cultivation.

2.2 Proper root trimming. Remove yellow and old leaves from the plants, keep the petioles at the root crown 2-3cm long, cut off the upper leaves, and pile large and small roots separately and force them separately so that the chicons are uniform in size. Note that the leaf stubble on the upper part of the root crown should not be left too long or too short; if too long, it easily rots during storage, and if too short, it easily damages the growing point and no marketable chicons can form.

2.3 Disinfection in advance. Before forcing cultivation, first disinfect the environment with 22% dichlorvos smoke agent at 500g/mu and 45% chlorothalonil smoke agent at 250g/mu, then soak the roots in warm water at 50-55°C to kill the fruit-borer pupae carried on the fleshy roots; then soak the root crown in 50% carbendazim WP at 500 times dilution to inhibit the occurrence or spread of sclerotinia and prevent rotting of the chicons.

2.4 Cultivation at suitable temperature. Soil temperature has a direct effect on witloof chicory chicons. Generally, forcing cultivation can be carried out at 4-21°C, and the forcing time varies with different varieties and temperatures; when the temperature is high, the time is short, and when the temperature is low, the time is long. When the temperature is relatively low, the chicons formed are crisp and tender, with less bitterness and good quality; when the temperature is high, the chicons formed are bitter and not crisp. Generally, keeping the temperature of the 10-15cm soil layer at 8-15°C is more suitable. The temperature level is mainly regulated by heating, covering and ventilation of the forcing site. For example, the temperature rise and fall in a solar greenhouse is regulated by how early or late the straw mats are uncovered and covered, the length of time the plastic film vents are opened and closed, and the size of the gaps.

2.5 Control humidity and prevent rot. The rotting of fleshy roots and chicons is mostly related to excessive temperature in the cultivation environment. In winter forcing cultivation, soil moisture loss is relatively small, so as long as the cultivation trench is watered thoroughly, no further watering is needed in between. After the water seeps down, bury the fleshy roots with fine soil up to the root crown, then cover with fine sand or sawdust 4-5cm deep. After 2-3 days, once the water vapor in the trench has dissipated, set up double layers of black film, with the film 30-40cm from the roots. Never allow water to accumulate in the surface soil of the fleshy roots, and do not cover with film immediately after watering the trench, as these will both increase the air humidity in the cultivation trench and cause rotting of the fleshy roots and chicons. During forcing cultivation, the relative humidity of the environment should preferably be kept at 85%-95%, and the air humidity level can be regulated by spraying water on the ground or ventilating at night.

2.6 No light throughout. The forcing site must remain absolutely dark. After covering the cultivation trench with black film, press the edges down firmly with soil, and also place straw mats on top to create a dark, moist forcing environment. Also reduce the number of daytime inspections of chicon growth to avoid the chicons turning green in the light.