What is Edema and What Causes it
Edema [Oedema] is [caused by] an irregular, abnormal, excessive water retention by plants. It is generally the result of environmental factors, such as heavy rains and wet weather sometimes coupled with over -watering by over-attentive gardeners. The plants basically become bloated and gorged with moisture.
A substantial difference between daily high and low temperature is also a contributing factor in edema. When watered late in the day, movement of fluid through the plant is reduced if the temperature drops quickly in the evening.
Plants will normally purge excess water via a process known as transpiration. Transpiration is the flow of water in the xylem tissues of plants. The process results in the evaporation of water from cell surfaces of leaves. At times the plants can't keep up.
Symptoms of Edema on Fruiting and Non-Fruiting Plants
In the case of some fruits such as melons, moisture surges, abnormal sudden accumulation of water can cause the fruits to engorge themselves to the point where the outer shell can not keep up and it basically pops open from from internal pressure. [See: Watermelons Bursting and Splitting ] The same can be observed in tomatoes and related fruits / vegetables. They get too much water and the inner flesh will expand faster than the outside skin can keep up with leading to split and cracked skins. [See: Why Tomatoes Split
Besides the scenario of cracking and splitting fruits other symptoms of edema on both fruiting and non-fruiting plants include .
Blistering and irregular bumps on the under sides of leaves caused by failure to expel excess moisture.
Water soaked blotches on foliage. Galls under leaves will correspond with yellow blotches on the leaves surface.
Cork-like spongey texture of plant tissue which will also diaplay unusual curling and other abnormal distortions.
Yellowing of foliage sometimes coupled with White, Some plants will exude water droplets while others will display crystalline eruptions along leaf veins.
Treatment of Plant Edema
Edema is not a disease in the classical sense being that it is not related to fungal or bacterial causes, but that gives little solice to the gardener who watches their plants fade and falter. Being that it is not a dsiease it is usually more easily treated. Once you have successfuly diagnosed edema you simply need to curatil your plants drinking problem. There's little you can do to stop Mother Nature from raining down upon them, but you can adjust watering habits.
Although edema is not a nutrient issue, it is at times related. Plants lacking in potassium and calcium are more susceptible to edema. Adjusting the pH will make more nutrients available, or you can add more of the nutrients that are lacking.
Root systems will absorb warm water faster when the air temperature is cool, so don't water until the sun is up and don't water in the evening after sunset.
For potted plants be sure they are draining well, there should never be a water build up in the planters base or saucers beneath them.
Humidity also plays a role in water retention. You can't do anything about outdoor humidity but for indoor plants you'll want to be sure there is adequate air circulation to decrease sitting stagnant humidity to suitable ranges.