What are the methods for preventing rice seedling-stage diseases?
I. Damping-off
Symptoms: During the seedling stage, the young shoots sometimes become discolored, the leaves curl, and finally the plants wither and die, spreading very quickly.
Control measures: The pathogen of damping-off survives in the soil, and the occurrence of damping-off is closely related to environmental conditions such as climate, seedbed temperature, soil pH, and fertilizer. Dry-raised seedlings are prone to the disease after a cold wave and low temperatures; when the seeding rate is high, management is poor, and the seedbed temperature is too high, spindly seedlings are prone to the disease; seedbed soil that is alkaline or neutral is prone to the disease; improper fertilization, especially the application of alkaline fertilizers such as human excrement and urine, urea, plant ash, and kang soil, is prone to cause the disease. To control rice damping-off, prevention should be the main approach: create good conditions that promote rice root development, strengthen seedbed management, control spindly growth of seedlings, cultivate strong seedlings, and enhance the disease resistance of the plants. At the same time, soil acidification and chemical control measures must also be used. After damping-off occurs, spray 75 g of 50% dexon plus 75 g of 77% Kocide per mu, diluted in 90-100 jin of water.
II. Bacterial wilt
Symptoms: The leaves curl, turn blue-green, and gradually wither and die.
Because the seedlings grow spindly and the root system develops poorly, when the film is removed for hardening the seedlings, the leaves transpire faster and the roots do not absorb enough water or absorb it poorly, causing the leaves to lose water, curl, and show bacterial wilt symptoms. Or, because of gaps where the seedbed is uneven, the roots cannot absorb water, resulting in physiological water shortage. Or the seedlings suffer strong low temperatures, their protoplasm is damaged, permeability increases, and water-holding capacity decreases; when the weather warms after cold, the temperature difference is too large, leaf transpiration strengthens, and the soil temperature is relatively low with poor water absorption, leading to physiological water loss and bacterial wilt.
Control measures: Nitrogen fertilizer should not be excessive. Harden the seedlings according to the weather to improve seedling quality.
III. Bakanae disease Symptoms: The most obvious feature is that diseased plants are slender and pale yellow.
Control measures: Bakanae disease is transmitted by seeds, and infected seeds are the source of infection. Strictly implementing seed disinfection is an effective measure to control this disease.