Technical Guidance on Field Management of Rapeseed During the Wintering Period (2015)

During this year's autumn sowing of rapeseed, the upper reaches of the Yangtze River basin received excessive rainfall, while in the middle and lower reaches the rice harvest period was delayed and a drought occurred in mid-October. The sowing and transplanting period of rapeseed was generally delayed compared with normal years, by about 10 days in the upper reaches and by about 5 days in some parts of the middle and lower reaches, resulting in large differences in the condition of rapeseed seedlings; in the upper reaches the population had 3-5 fewer leaves than last year, and in some late-transplanted rapeseed in the middle and lower reaches the seedling age was short, the seedlings were small and the seedling quality was weak. According to the forecast of the China Meteorological Administration, the El Nino event may intensify this winter, and there is a high probability of low-temperature overcast rain and a warm winter. In order to guide all localities in effectively carrying out classified guidance on rapeseed seedling condition, the National Agricultural Technology Extension Service Center, together with the Oil Crops Expert Guidance Group of the Ministry of Agriculture, studied and put forward this technical guidance on field management of rapeseed during the wintering period.

(1) Timely thinning and replanting of seedlings and rush transplanting. For directly sown and early transplanted rapeseed, start thinning and replanting seedlings early from the 3-leaf stage, removing weak plants and keeping strong ones, removing mixed plants and keeping pure ones, removing small plants and keeping large ones, removing diseased plants and keeping healthy ones, and removing dense plants and keeping an even stand; final thinning should be done at the 4-5 leaf stage. For directly sown rapeseed, generally retain 12,000-30,000 plants per mu; for transplanted rapeseed, ensure a field density of 6,000-8,000 plants. For rapeseed fields in the lower reaches that have not yet been transplanted, seize the favorable opportunity of recent increased rainfall and improved soil moisture to rush to transplant early while the soil moisture is adequate, and appropriately increase transplanting density to compensate for lateness with density. Generally, no fewer than 7,000 plants per mu, with a maximum of 10,000 plants.

(2) Clean ditches early to drain waterlogging and prevent drought. During the onset of winter, the Yangtze River basin often experiences continuous overcast and rainy weather, and low-lying fields are prone to waterlogging disasters, causing oxygen deficiency, root rot and weak seedlings in rapeseed, reducing cold resistance during wintering, aggravating the occurrence of sclerotinia, and affecting yield and quality. In the upper reaches, there was excessive rainfall during the sowing period, and drought may occur in winter; once a strong cold wave occurs, drought and freezing may be superimposed. Therefore, before the onset of winter, the three ditches should be installed early, and the surrounding ditches should be cleaned in time to ensure smooth drainage and irrigation.

(3) Carry out fertilizer and water management well according to seedling classification. After transplanted rapeseed turns green or directly sown rapeseed is thinned to a final stand, promptly apply a seedling-promoting fertilizer at 5-6 kg of urea per mu; from late December to early January, apply heavy winter fertilizer according to seedling condition and growth, with 5-7 kg of urea and 3-5 kg of potassium chloride per mu. For rapeseed with sufficient base fertilizer, sufficient density and robust growth, the seedling and winter fertilizer may be omitted; for directly sown rapeseed without base fertilizer or with insufficient base fertilizer and a late sowing period, as well as rapeseed with slow growth and stunted seedlings that do not grow, apply seedling fertilizer as early as possible, about 7.5 kg of urea per mu, to promote growth and transformation; for fields with uneven growth, additional seedling fertilizer may be applied as appropriate to promote balance.

(4) Spray regulators to control excessive growth and promote strong growth. Before the onset of winter, spray growth regulators such as Bihu and Painuoke, using the standard dosage per mu diluted in 40 kg of water for spraying, to promote winter growth and improve cold resistance during wintering. For rapeseed with excessive growth, spray 30-40 g of 15% paclobutrazol per mu diluted in 40 kg of water to control excessive growth and promote strong growth, prevent early bolting and early flowering, improve plant cold resistance, and achieve overwintering with strong seedlings.

(5) Strengthen management of diseases, insect pests and weeds. Affected by climatic conditions and field soil moisture, weed damage occurs early and quickly in the upper reaches, monocotyledonous weeds in rice fields are relatively severe in the middle reaches, and the weed base is large in some no-till rapeseed fields in the lower reaches. For fields where closed weeding has not been carried out, spray as soon as possible with 20-30 ml of high-efficiency gallant per mu diluted in 30 kg of water to control grass weeds, and 30 ml of Gaoteke diluted in 30 kg of water to control broadleaf weeds. During the seedling stage, mainly control damping-off and downy mildew; damping-off can be controlled with 95% hymexazol fine powder at 4000 times dilution; if large-scale downy mildew occurs, metalaxyl-hymexazol can be used for control. During the bud and bolting stage and early flowering stage, mainly control sclerotinia; when the leaf incidence of sclerotinia reaches 10%, spray the leaves with 80% carbendazim ultrafine powder at 1000 times dilution, or 40% dimethachlon wettable powder at 800 times dilution, or thiophanate-methyl suspension concentrate (36% active ingredient) at 1000 times dilution, and apply again after an interval of 7 days. In addition, in the upper reaches of the Yangtze River, the Yichang area in the middle reaches of the Yangtze River and other areas, strengthen the control of rapeseed clubroot; lime nitrogen can be used to replace traditional nitrogen fertilizer as a topdressing, and chemical control can be carried out by drenching with 50% carbendazim at 600 times dilution or dexon at 500 times dilution.