Causes and Control Methods of Buttoning and Yellowing in Broccoli
Broccoli is an annual or biennial herbaceous plant native to the eastern Mediterranean coastal region. It is cultivated on a small scale in China, mainly for use in Western cuisine. Broccoli is rich in nutrients, containing protein, sugar, fat, vitamins and carotene, and ranks first among vegetables of its kind in nutritional content, and is known as the “crown of vegetables”. It is a variety of the cabbage species in the Brassica genus of the Brassicaceae family, with green heads as the product. It originated in the Italian region along the Mediterranean coast of Europe and was introduced to China at the end of the 19th century.
Growth Habits of Broccoli
Light
Broccoli is not very strict about light requirements, but it prefers sufficient light during growth. When light is adequate, the plant grows robustly and can form a strong vegetative body, which is beneficial to photosynthesis and nutrient accumulation, and makes the heads compact and dense with a fresh green color and good quality. Too strong sunlight in midsummer is also unfavorable to the growth and development of broccoli.
Temperature
Within the range of 5—20°C, the higher the temperature, the faster broccoli grows and develops. The optimum germination temperature is 20—25°C, and the optimum growth temperature during the seedling stage is 15—20°C. Broccoli has strong cold and heat tolerance. The optimum growth temperature during the rosette stage is 20—22°C, and the optimum temperature for head development is 15—18°C. When the temperature is higher than 25°C, head quality tends to deteriorate, but as long as it is not damaged by frost, the head can still grow slowly at low temperatures of 5°C or even below. Different varieties and different seedling ages have relatively large differences in the temperature requirements needed to complete vernalization, so the selection of varieties is very important for year-round cultivation.
Water
Broccoli requires a relatively large amount of water throughout its growth process, especially during vigorous leaf growth and head formation, when water shortage must be avoided. Even short-term drought will reduce yield. Rainy weather during the seedling stage or excessively high soil moisture can easily cause diseases such as black rot and black spot. During head formation, the soil moisture needs to be about 70—80% of field capacity to meet growth needs.
Soil
Broccoli is not strict about soil conditions, but overly poor soil leads to poor plant development and low yield and quality, while overly fertile soil can cause loose buds and hollow flower stalks. Broccoli is suitable for planting in loam and sandy loam with good drainage and irrigation, deep plough layer, loose and fertile soil texture, and strong water and fertilizer retention. It adapts to a soil pH range of 5.5—8, but 6 is best. Broccoli requires sufficient fertilizer throughout its growth process, with an N, P, K ratio of 14:5:8. During the seedling stage, the demand for nitrogen is relatively greater, and after flower bud differentiation begins, the demand for P and K relatively increases. Note that during head development, broccoli also requires relatively large amounts of trace elements such as boron, molybdenum and magnesium, so applying appropriate trace element foliar fertilizer before budding will significantly improve yield and quality.
Causes and Control of Buttoning and Yellowing in Broccoli
During cultivation, broccoli often produces fuzzy heads or forms buttoned heads, and some heads are loose, with buds withered or yellowed. When this happens, it seriously affects the edible value and marketability of broccoli.
Causes of buttoning and yellowing in broccoli. Broccoli is suitable for summer and autumn cultivation. When cultivated in early spring, its early growth period is in a low-temperature period. Although the plant grows slowly, low temperatures favor flower bud differentiation, so budding occurs early and small heads are easily produced. However, in the later growth period, when it enters a high-temperature period or the greenhouse temperature is too high, bud development is inhibited, and abnormal heads such as fuzzy heads and buttoned heads easily appear. Near the head harvest period, when the temperature rises, the heads grow and develop quickly. If not harvested in time, the buds become loose and tend to yellow. Especially when daytime temperatures are too high, the heads wither and yellow, and long storage time also easily leads to the above conditions. The disease is more severe in off-season cultivation.
Control methods for buttoning and yellowing in broccoli:
(1) Choose mid-early maturing varieties or early maturing varieties that are not very sensitive to low temperatures in the early growth stage, such as Luling, Shanghai No. 1, Ludi, Qinglu, Zaoshenglu, etc.
(2) Sow at the appropriate time. If sown too early, because the temperature is low after planting, the plant's flower buds differentiate upon encountering low temperatures. At this time, nutrition is insufficient, with few and small leaves, leading to early budding and small heads. If sown too late, the temperature rises rapidly, and the bud development period coincides with a high-temperature period, which easily causes high-temperature stress, producing buttoned heads.
(3) Cultivate strong seedlings, mainly through temperature management. After sowing, maintain the night temperature above 12°C and the daytime temperature below 30°C. When there are 5-6 true leaves, plant at the appropriate time. If too late, the seedlings age and the heads are small. Plant about 3000 plants per 667 sq m.
(4) If the harvest period is in a high-temperature stage, harvest must be done at the appropriate time, and it should be arranged in the morning to avoid withered buds and yellowing and to prolong the freshness time of the heads.
(5) Broccoli should not be stored for long, and should be eaten as soon as possible after harvest.