Oedema
Description
Oedema occurs when plants take up more water than required for transpiration of the leaves. Often occurs in plants grown under glass when the soil is warm and moist, but the air is cool but saturated.
Symptoms
Small blisters of excess water turn into brown wart-like marks on the underside of leaves and sometimes on stems and petals of flowers.
Treatment and control
General tips
Overwatering and high humidity cause the problem, so encourage more movement of warm air and allow the compost at the roots to dry out between watering. More space between plants will reduce humidity at the leaves.
