Key Technical Points for Field Management in the Late Growth Stage of Winter Rapeseed

Rapeseed in the field has now entered the late growth stage, with both vegetative growth and reproductive growth very vigorous. This is an important period for increasing the seed-setting rate and oil content and for boosting grain weight, and it is crucial for yield formation. The main late-stage field management techniques for winter rapeseed are:
1. Adapt measures to local conditions and apply flower and grain fertilizer judiciously. Rapeseed takes about 60 days after the start of flowering to mature, and during this time it still needs a large amount of nutrients. Topdressing with flower fertilizer is an important measure for increasing yield in the late stage of rapeseed. The application of flower fertilizer should be determined according to seedling condition, soil fertility and other conditions. For fields with sufficient early fertilization and vigorous rapeseed growth, 0.2 jin of potassium dihydrogen phosphate per mu can be mixed with 100 jin of water for foliar topdressing and sprayed evenly, which can both prevent premature senescence and promote the synthesis and conversion of fat in the seeds, increasing the oil content of the seeds. For fields with little early fertilization and poor rapeseed growth, 3-4 jin of urea per mu can be topdressed before rain at the start of flowering to supplement nitrogen fertilizer. For fields showing premature senescence, pale leaf color and an early end of flowering, 2 jin of urea per mu can be topdressed at the end of flowering, or 0.1 jin of urea and 0.2 jin of potassium dihydrogen phosphate per mu can be mixed with 100 jin of water and sprayed evenly. Care must be taken to prevent excessive nitrogen fertilizer application in the middle and late stages, which can cause the plants to remain green late, increase shriveled seeds and reduce fat content.
2. Prevent drought and waterlogging, and prevent lodging. In the northern winter rapeseed region, drought is often encountered in the middle and late stages, so irrigation should be carried out in time to resist drought and maintain a certain level of field moisture. In the southern winter rapeseed region, there is relatively more rain in the middle and late stages, so ditches should be cleared in time to drain water and reduce humidity, control the groundwater level, keep the three ditches unobstructed, and prevent waterlogging and disease. In the middle and late stages of rapeseed, a relative field water content of 60%-70% is generally sufficient.
From the end of flowering to the point when the siliques are basically set, rapeseed is prone to lodging and breaking, especially in fields where the plants are overgrown, the density is too high, transplanting was too shallow, earthing up was insufficient, drainage is poor, or there is damage from sclerotinia, or when heavy rain and strong winds occur. Lodging causes the rapeseed stems to break, nutrients cannot be transported normally, photosynthesis in the lower siliques weakens, ventilation and light penetration in the field are poor, and the plants are susceptible to disease and mildew, seriously affecting the yield and quality of rapeseed. In the middle and late stages of rapeseed growth, the three ditches should be kept unobstructed and soil should be earthed up around the roots in time. For fields with vigorous growth, preparations should be made in advance to use bamboo poles for support.
3. Remove old yellow leaves and prevent and control sclerotinia. Sclerotinia is the most important disease in rapeseed production and can cause 10%-30% yield loss, or even higher, and it is most likely to occur during the flowering stage and silique development stage. On sunny days, old yellow leaves on the middle and lower parts of the plants should be removed in time and taken out of the field to improve ventilation and light penetration and prevent disease. For fields with good growth and early and severe incidence, removal should be done early; for fields with poor growth and mild incidence, removal should be appropriately delayed or not done. When the leaf incidence rate of plants in the field reaches 10% and the stem incidence rate reaches 1%, pesticide should be sprayed promptly on sunny days for control. Per mu, 0.2-0.3 jin of 50% carbendazim wettable powder or 0.2-0.3 jin of 40% dimetachlone can be mixed with 100 jin of water and sprayed evenly, focusing on the middle and lower stems and leaves of the plants and the ground. For fields with excessive growth, pesticide should be sprayed once more after an interval of 7-10 days to improve the control effect.
4. Promote early maturity and harvest at the right time. For rapeseed whose maturity period is delayed and affects crop rotation, about 20 days after the end of flowering, 100 jin of 3000-4000 ppm ethephon solution per mu can be sprayed to promote early maturity and ease the conflict in crop rotation.
When 2/3 of the siliques in the whole field are yellow-green, the siliques in the middle of the main axis are loquat-colored, and 1/3 of the siliques on the whole plant are still green, this is the suitable harvest period for rapeseed, generally about 25-30 days after the end of flowering. The suitable harvest period for rapeseed is relatively short, so the timing must be grasped well, and harvesting should be done on a sunny morning with dew to prevent the siliques from splitting and shedding seeds. The cut rapeseed should be transported out of the field in time and stacked in alternate layers, and covered with rice straw or plastic film. When stacking, the siliques should be placed inside the stack to facilitate after-ripening. Generally, after stacking for 4-6 days, seize a sunny early morning to spread the stack, sun-dry, thresh, dry and winnow clean in time.