In
order to stand upright and crisp, plants fill their
cells and tissue with water that forms what is called
turgor pressure. If there is not enough water present
for the plant to maintain this pressure, the plants will
begin to wilt.
Wilt may be caused by
many different factors. The most obvious one is the lack
of water in the soil because of drought or the excessive
loss of water because of hot weather. Sometimes these
causes can be overcome simply by providing more water to
the roots.
However, there are times
when irrigating the plant is not enough. Remember that
water moves through a plant in "pipes" of varying sizes.
These have been developed over the eons to provide
enough water to that species of plant during a "typical"
growing season in the local region. On days with
exceptionally high temperatures and low humidity, there
may just not be enough capacity in the pipes to keep up
with the water loss through the leaves by transpiration.
Wilt Diseases -
There are a handful of diseases which are truly life
threatening to trees. Most plant diseases tend to be
chronic and cumulative over years but a few are
relatively quick killers and these commonly fall into
the category of wilt diseases.
Plant diseases that fall
into this category are primarily caused by fungi. Once
inside the tree, they are very, very difficult
(sometimes impossible) to cure or control. Wilt diseases
tend to kill trees by one of two ways:
1.
Disease Kills the Tree - Most of the diseases
produce gooey substances that will clog the
xylem and
phloem. This prevents the transport of water and
nutrients so the part of the tree served by those
blocked tissues must die. Eventually, the main trunk is
totally affected and the entire tree dies.
2.
Tree Kills the Tree - One of the ways trees
survive is by having the ability to "compartmentalize"
parts of the tree that are suffering from disease. Once
a rot or other internal infection is sensed by the tree,
it can set up an impenetrable barrier around the
problem. This is why trees can have areas of rot but
generally do not completely rot away. When certain wilt
diseases get started, the tree's self-defenses may kick
in the tree itself will block parts of its water
transport system.
Here are some of the more
common wilt diseases:
