| Oedema is a physiological disorder that develops
when roots take up water faster than it can be used
by the plant or transpired through the leaves. Water
pressure builds up in the internal cells of the leaves
causing them to burst, leaving dead cells that are
visible as a blister, primarily on the undersides of
leaves. Oedema may also be spelled edema.
Geraniums, rhododendrons, begonias, peperomias,
jade plants, ficus, schefflera, and camellias are
particularily sensitive to conditions that lead to the
development of oedema, although almost any
broadleaf plant may be affected
Symptoms and Diagnosis
These blisters eventually erupt and form white, tan,
or brown wart-like corky growths. As the condition
worsens, leaves may turn yellow, droop, and fall off.
In severely affected plants, blisters also form on the
petioles and stems, although this is more rare. The
upper surfaces of these leaves will often have
indentations above the engorged cells on the
undersides. If the problem is not corrected, the
plants will become spindly.
On indoor plants, oedema is most prevalent in the
late winter, especially during extended periods of
cloudy weather. It is likely to develop when the soil
is warm and the air is cool and moist. This
environment results in rapid water absorption from
the soil and slow water loss from the leaves. These
conditions are most frequently encountered in
greenhouses or indoor situations rather than
outdoors but oedema can also be common on
container-grown plants.
Integrated Pest Management Strategies
1. Culture. Oedema is a cultural problem so cut
back on watering, but avoid letting plants dry out
completely. If necessary, move the plant to a
larger pot if it dries out too quickly.
2. Greenhouse conditions. When symptoms occur
in a greenhouse, promote conditions that allow
water loss to balance with water uptake by the
roots. Decreasing humidity forces higher
transpiration; ventilation is important as well as
air temperature. |
