-- The total impact of chemical damage is unknown. Large losses have
occurred in very localized areas. The losses normally can be traced
to a point source such as a chemical spill or industrial waste. Not
as easily recognized but perhaps more damaging are the non-point source
pollutants such as those associated with a large city. Many oak species
decline, dieback and succumb over a period of years. On the other hand,
some oak species are relatively resistant to many pollutants and are
the Causal Agent. -- Chemicals reach the tree in a variety of forms
through the air or soil. Several conditions must
occur to cause damage. There must be a susceptible host in a receptive
condition, and the chemical must arrive in a quantity and form that
will affect the host. Some chemicals damage on
contact, others interact with tree processes.
the Injury (figure 73). -- Most chemicals have certain characteristic
symptoms. Ozone causes small bleached or pigmented spots on the upper
leaf surface. Sulfur dioxide kills tissue between the leaf veins. Fluoride
kills tissue on the leaf margin or between the veins. Ammonia causes
faded leaf margins and dead or dying tissue with green islands mostly
near veins. Herbicides cause blotchy dead areas on the surface of mature
leaves; expanding leaves curl and become distorted.
Because of great variation of susceptibility among trees
and the combination of chemical and climatic factors,
diagnosis is complex. Thus, proper diagnosis may require a person with
extensive training and experience.
-- Protect from chemicals or plant resistant trees.
73. -- Chemical damage -- due to ammonia