Rapeseed often form a large number of “red leaf seedlings†in winter. The causes and corresponding control measures are:
The nitrogen-deficient plants are dwarf, the new leaves grow slowly, the leaves are small and small, yellow-green to yellow, and the leaf margins are red.
Control measures: Measure 8-10 kg of urea per mu or 20-30 kg of ammonium bicarbonate, or use 750-1000 kg of human feces and urine to pour water; apply nitrogen at a later stage and spray with 1%-2% urea solution.
When sulfur-deficient rapeseed lacks sulfur, the plants are dwarf and pale green, which is similar to nitrogen deficiency disease. The leaf margins are greatly nicked and crumpled into cups. The back, veins, and stems of the leaves turn purple.
Prevention and control measures: In combination with cultivator, 1-2 kg of sulfur powder or 50 kg of gypsum powder shall be applied per acre.
Boron-deficient rape is a boron-rich crop, and its dry matter contains 32.5-36 times more boron than wheat, rice, and other grasses. When boron is deprived, the leaves initially turn dark green, the leaf shape becomes smaller, and the leaf quality becomes thicker and changes. Crisp, reversal of leaf tip, shrinkage and unevenness. Then it turned purple from the edge of the lower middle of the leaf, and developed into the interior, and then became blue-purple; the yellow veins and its nearby tissues turned yellow, resulting in the formation of blue and purple patches. Finally, some leaf margins die and the entire leaf turns yellow and falls off early.
Control measures: Foliar spraying with 0.1%-0.2% borax solution.
The drought of rapeseed during the seedling stage and the lack of soil moisture will make it difficult for the roots of the rapeseed to suck up and absorb water, which results in the slow growth of the rapeseed, the dwarfness of the plants, and the turning of the leaves into pale red.
Prevention and control measures: Watering in time, furrow irrigation should be taken when watering, do not flood irrigation, to prevent rot dead seedlings.
If there is too much rain before winter, or if transplanted in paddy field, the filter water will not be smooth, causing waterlogging and root damage. The leaf color will turn dark red, and some will still be dead.
Prevention and control measures: timely drainage of water to reduce the groundwater level; cultivating loose soil, improve soil permeability conditions, and promote root development.
When the freezing temperature suddenly drops below 0°C in winter, the leaves will also appear red when they are frozen.
Prevention and control measures: Combine with cultivator clearing ditch, planting soil and removing roots, adding organic fertilizers to reduce freezing damage.
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