Page 73 - ORNAMENTALES DEL TRÓPICO

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identiFication and management oF ornamental Plant disease ProBlems

die. As large numbers of adjacent cells die, the damage (necrosis) becomes visible to the naked eye.
Hence, one of the major symptoms of frost or freeze injury is areas of necrotic tissue, especially at

leaf tips and margins.

Excessively high temperatures may also damage plants. In this case, proteins may become

denatured and coagulate. Tissues dry out and die. Whitish, papery appearing areas on leaves

are often a symptom of damage due to high temperature.

Moisture extremes may also adversely affect plants. With insufficient amounts of water

comes obvious wilting of plants. If stems of affected plants are cut open, vascular tissues ap-

pear as more or less healthy looking light colors (off-white in herbaceous plants, light brown

in woody plants).
Excessive water may also be a problem and this disorder is very common in the landscape

and production nurseries throughout south Florida. A specific case of plant injury associated

with too much water is oedema. This occurs most often on ornamental foliage plants with

thicker leaves. Prolonged periods of overcast, rainy weather lead to reduced evaporation of

water from plant containers and reduced natural water loss (transpiration) from leaves. Howe-

ver, if water uptake from the roots remains the same, plant tissues can become engorged,

leading to rupturing of cells, producing brownish lesions that can resemble damage caused by
fungi. Roots that sit in waterlogged soil long enough can actually wilt, will lack vigor, and deve-

lop light green or pale yellow-green areas in leaves. This is probably due to collapse of root

cells because of lack of oxygen. Oxygen-starved roots do not function properly leading to the

wilt and other symptoms just described.

Low light regimes lead to reduced formation of chlorophyll and subsequently a possibly

undesirable plant that is lighter green than normal. Plants may become etiolated; i.e., they

develop a “leggy” or spindly appearance because the length of stems between internodes

Universidad Autónoma de Chiapas