Pepper purpura is also known as anthocyaninosis.
Purple patches appear on the green surface of the fruit. The patches have no fixed shape and vary in size. The amount of purple on a fruit ranges from one piece to several. In severe cases, even half of the fruit may be covered with purple spots. Sometimes fan-shaped purple pigment appears along the midrib on the top leaves of the plant, which expands into purple spots.
Due to the difficulty in plant roots absorbing phosphorus, anthocyanins appear. Phosphorus deficiency occurs in old vegetable plots that have been grown for many years. Insufficient water in the soil or low temperature will lead to insufficient supply of available phosphorus in the soil or difficulty in absorbing it. Especially when the ground temperature is lower than 10°C, it is easy to cause difficulty in absorbing phosphorus by the plant roots.
When the protected land is cultivated early in spring or delayed in autumn, it is necessary to do a good job of increasing the temperature and keeping it warm. Raising the ground temperature to above 10°C will prevent the production of anthocyanins and the formation of purple spots. Apply more farmyard manure to increase the effective supply of phosphorus in the soil. Pay attention to the application of magnesium fertilizer, because magnesium deficiency will inhibit the absorption of phosphorus. During the fruit growth period, spray potassium dihydrogen phosphate 200 to 300 times in a timely manner.