Key Technical Points for Cold and Frost Protection of Rapeseed in Early Spring

I. Clear ditches and earth up soil to prevent waterlogging damage. Promptly clear the "three ditches" to reduce field humidity and prevent waterlogging damage. In conjunction with clearing ditches, earth up around the roots of fields where growth is excessive or too weak, to reduce damage to the root system from frost.

II. Remove frozen bolting stems (and leaves) to reduce losses. For the small number of rapeseed plants that have bolted and flowered early, it is recommended to remove them promptly, pinching off the tips and breaking off the bolting stems. For early-bolted and early-flowering rapeseed that has already been frost-damaged, choose a sunny day to promptly remove the frozen bolting stems, to promote branch growth at the base of the plant and compensate for frost damage losses. When removing frozen bolting stems, cut about 2 cm below the dead stem section, using scissors or a sickle with a slanted cut, and promptly remove frost-damaged leaves that show obvious water-soaked appearance, to prevent frost injury from affecting the entire plant. Leaves that have obviously turned white or dried up should be removed promptly. The removed frozen bolting stems and frozen leaves must be cleaned up thoroughly and must not be left in the rapeseed field. Removing frozen bolting stems and clearing dead leaves must absolutely not be done when dew has not yet dried, to avoid wound rot.

III. Apply supplementary topdressing to promote recovery. After rapeseed is frost-damaged, both leaves and roots suffer damage to varying degrees, and nutrients must be supplemented promptly. For fields where frozen bolting stems have been removed, apply 5-7 kg of urea per mu or an equivalent amount of compound fertilizer as topdressing depending on the situation, to promote branch growth. For rapeseed with frost-damaged leaves, apply 3-5 kg of urea per mu or an equivalent amount of compound fertilizer; for fields with poor growth, the amount of topdressing can be appropriately increased to help them recover growth as soon as possible. On the basis of nitrogen topdressing, an appropriate amount of potassium fertilizer should also be supplemented; 3-4 kg of potassium chloride can be applied per mu, or about 500-800 g of monopotassium phosphate can be sprayed on the foliage in combination with pest and disease control, to enhance the plant's cold resistance and promote grain filling and plump seeds. In addition, spray about 50 kg of 0.1%-0.2% boron fertilizer solution per mu on the foliage to promote flower bud differentiation.

IV. Control pests and diseases to ensure a good harvest. After rapeseed is frost-damaged, wounds increase, making it more susceptible to infection by diseases such as sclerotinia. It is necessary to strengthen forecasting and monitoring of pests and diseases, pay close attention to disease occurrence trends, and promptly spray pesticides such as dimethachlon, thiophanate-methyl and mancozeb for control.