What are the control methods for pepper seedling leaf curl disease?

When peppers are grown as seedlings in winter and spring, after transplanting (dividing seedlings) leaf curl, arrested growth and even death often occur.

I. Causes and symptoms

(1) Physiological disease: long-term low temperature and high humidity in the seedbed cause poor plant development, yellowing of stems and leaves, curling and shrinking of the terminal leaves, and stunted growth; in severe cases the roots are waterlogged and rot, the roots turn rusty in color and then decay. (2) Viral disease: pepper viral disease in greenhouses and plastic tunnels occurs in all four seasons; the terminal leaves of diseased plants shrink, curl and take on a fern-like shape. (3) Damage by the broad mite (tea yellow mite): the leaf margins of young leaves curl downward, the underside turns brown and oily in appearance, and in severe cases the terminal buds dry up. (4) Damage by aphids: at first the leaves curl and become deformed, then because of contamination by insect droppings the leaves become covered with an oily substance and turn black.

II. Control measures

1. Eliminate low temperature and high humidity: let sunlight shine on the seedbed fully; during consecutive overcast, low-temperature weather, add warming facilities. Do not ventilate after transplanting (dividing seedlings); keep the seedbed temperature at 25-30 degrees C during the day and 18-20 degrees C at night. If the temperature is too high at midday, cover with straw mats for shade and make the seedbed receive heat evenly; if the nighttime temperature is too low, cover early and cover with more straw mats to keep warm. After the seedlings have recovered from transplanting, lower the day and night temperatures by 3-5 degrees C, and scatter dry plant ash or fine dry soil on the seedbed to absorb moisture and raise the temperature. Spray the leaves with a 500-fold dilution of photosynthetic micro-fertilizer or a mixed solution of monopotassium phosphate and urea to promote growth. For small, old seedlings, spray a gibberellin solution at a concentration of 15 mg/kg to promote sprouting.

2. Control of viral disease: spray a mixed solution of 20% Virus A and Panshibao (50 kg of water plus 100 g of Virus A and 5 mL of Panshibao), or a 300-fold dilution of 5% Huanzhongjunduqing, or an 800-fold dilution of 1.5% Zhibingling emulsifiable concentrate, once every 7 days, spraying 3-4 times in succession.

3. Kill the broad mite (tea yellow mite): spray the underside of the leaves with a 300-fold dilution of 15% pyridaben emulsifiable concentrate, or an 800-fold dilution of 20% dicofol emulsifiable concentrate, or a 2000-fold dilution of 20% fenpropathrin.

4. Aphid control: spray a 2000-fold dilution of 2.5% bifenthrin (Tianwangxing) or 50% pirimicarb.