DISEASE

NAME
Oedema
Environmental (Water)


Description
This is an environmental problem relating to excessive water. It occurs when the roots take up water faster than the plant can transpired through the leaves. This build-up of water in the leaf and stems, courses swelling of the epidermal layer.

Symptoms
The leaf or needle underside develops small brown to white corky areas that have a scabby appearance. When the injury occurs excessively the leaves turn yellow droop and then fall off. These symptoms may also appear on the petals of the flowers and the stems causing the plant to become spindly and reduces growth. It commonly occurs in damaged areas of the leaf ie: torn or broken leaf parts and where insects have attacked.

Begoniaspecies     Camellia species
Image by B. Sonsie

Source and Dispersal
This is an environmental problem relating to excessive moisture or humidity and as such has no direct source.

Favoured Conditions
It prefers a high humidity low light environment and is triggered by over watering as in a humid glasshouse or when plants are grouped together with poor air circulation. It is most prevalent outdoors during late winter to early spring during cool, cloudy weather when the soil is moist and warm.
     
Affected Plants
There are many plants that are sensitive to these conditions and included geraniums, rhododendrons, begonias, pansies, violence, and fleshy leaf plants such as Jade or pepperomia. Vegetables such as tomatoes and cabbages are also affected.

Begoniaspecies are affected by forming a Corky Scabon leaf undersides and down the stems as a direct result of Oedema.

Corky Scab     

Cactusspecies are infected by Corky Scab, which is seen as rusty or corky spots along the stems with the epidermal layer becoming dry then breaking open and curling. The spots as soon form a thick covering with only the new growth free. Under extreme conditions it will kill plant and mild infections reduce flower production. Control methods include increasing the light, decrease in humidity and improving air circulation. A similar appearance on cactus may result from overexposure to direct hot sun. It appears as sunken brown or white patches developing on one side of the stem where the chlorophyll has been destroyed (cooked).


Corky Scab on Cactus

Camellia species are particularly susceptible but it also affects Gardenia,Acalyphaand Scheffleraspecies.

Camelliaspecies

Non-chemical Control
Remove and destroy affected leaves and regulate watering of the plant by not over watering or watering at night. Water should be reduced during winter for susceptible plants and under glass, keep the humidity below the 70% with good ventilation.

Chemical Control
There is no effective chemical control.